Completed Research Projects

A CIP-HIP Method for the Production of Near Net Shaped Titanium Components

Researcher: Fatos Derguti
Supervisors: Dr Richard J Dashwood, Dr Martin Jackson, Dr David Dye and Professor Malcolm Ward Close (QinetiQ)
Sponsors: EPSRC (Case Studentship), QinetiQ

The recent emergence of a number of novel low cost production methods for titanium alloy powders has stimulated significant interest in the near net shape production of titanium components via powder metallurgy. This project is concerned with the development of a new route for titanium parts based on a multi-stage forming and consolidation process using both cold and hot isostatic pressing. Commercial purity titanium and Ti-6Al-4V powders of varying particle size distributions are being cold isostatically pressed at a number of compaction pressures using different bagging materials. The resulting compacts are then being indirectly hot isostatically pressed using a process intended to achieve full material density without the need for expensive metal cans. The importance of the cold isostatic pressing variables and in particular the bagging material, on achieving sufficient green strength for further processing are being investigated. The benefits of this process with respect to the microstructure and properties of the final product are also being evaluated.

Alloys by Design: Coupling Quantum Mechanical Models into Microstructural Simulations for the Prediction of Complex Microstructures

Researcher: Stefano Angioletti-Uberti
Supervisors: Professor Peter D Lee and Professor Mike W Finnis
Sponsor: EPSRC (Project Studentship)

This is part of a larger project developing an integrated multiscale modelling framework over the atomistic, defect and continuum length scales relevant to materials with heterogeneous microstructures. Working with researchers at Oxford, Cambridge, Birmingham and the industrial collaborators of Rolls-Royce and Siemens, this project is predicting: liquid state diffusion coefficients and solid-liquid interfacial energies from linked ab initio and molecular dynamics calculations, which will be used to simulate crystal formation during solidification, predicting microstructure, phase and composition using in-house microstructural modelling techniques. The models developed are being coupled into micromechanics models but experimental validation with existing data, and the design of new experiments is a key aspect. The final goal of the overall project is to open up as yet unexplored avenues in materials engineering, leading to true computational materials design.

Calculating Liquid State Thermophysical Properties from First Principles

 

Researcher: Stefano Angioletti-Uberti
Supervisors: Professor Peter D Lee and Professor Mike W Finnis
Sponsor: EPSRC (Project Studentship)

Modern day single crystal Ni-base superalloy turbine blades suffer from defects arising during solidification (e.g., freckles). These defects may cause premature failure of the blade during service, thus the defective piece must be remelted increasing production costs. Freckle formation depends on preferential partitioning of elements during the solidification process; therefore a knowledge of the partition coefficients is required to engineer alloy compositions and casting procedure to avoid defect formation. Calculation of partition coefficients is possible using atomistic modelling and statistical mechanics. However, the accuracy of the calculated value depends on the reliability of the energetic description of the alloy, and ab-initio modelling is thus the best candidate for this purpose. Lower level approaches based on empirical potentials would be much faster due to their lower computational cost, but do not have the same accuracy. We show here that it is possible to combine both strengths of the two modelling approaches to calculate partition coefficients with an ab-initio accuracy in an efficient way by a free energy perturbation approach. The simulations, made using different embedded atom method potentials, show that it should be effectively possible to apply our technique to ab-initio calculations. This procedure will be applied to actual ab-initio calculations in the near future.

Alpha Case Formation in Titanium Alloys

Researcher: Meurig Thomas
Supervisors: Dr Martin Jackson and Professor Trevor C Lindley
Sponsor: EPSRC (Case Studentship), Rolls-Royce plc

Titanium alloys are widely used for manufacture of compressor components for aeroengine gas turbines combining low density with good resistance to creep, fatigue and environmental degradation at elevated temperatures. However, during exposure in oxidising atmospheres at temperatures up to 900 K, inward diffusion of oxygen can result in the formation of an all alpha surface layer. The depth of this surface layer called the alpha case increases with increasing exposure time and temperature. This alpha layer is brittle and mechanical properties can be significantly degraded. This project is improving our understanding of the formation kinetics of alpha case and the subsequent effects on mechanical performance. A parametric study is being carried out to determine the effects of temperature, time, alloy chemistry (i.e., four different alloy classes; CP Ti, IMI 834, Ti-6Al-2Sn-4Zr-6Mo, Ti-10V-2Fe-3Al) and degree of surface deformation (i.e,. intensity of shot peening) prior to thermal treatment. After thermal treatment, a sequence of room temperature tensile loading and high cycle fatigue testing is being applied to 1) determine the nature of crack nucleation/growth and; 2) quantify the cracking size/density in the alpha case and subsurface region. Furthermore, thermal compression loading in conjunction with room temperature tensile straining will be carried out to provide underlining microstructural and cracking information for more complex thermomechanical fatigue investigations and modelling.

Tansel Arif - Mesoscale modelling of steel processing

Investigator: Tansel T Arif

Supervisors: Dr Rongshan Qin

Duration: 01/09/2011 - 01/07/2014 (PhD Studentship)

Description:Within the area of materials science there is an increase of interest in modelling techniques that can accurately predict the microstructure of a material subject to various processing conditions. The phase-field method, a popular technique used in this area, has been shown to have the ability to cope with phase transformation dynamics such as solidification and solid-state phase transformations. However, its predictive capabilities apply to a flow free environment where flow effects are minimal compared to other effects. Other techniques such as Smoothed Particle Hydrodynamics (SPH) exist that are more than capable of describing the mechanisms of flow. The aim of this project is to develop a model to describe the evolution of steel from its molten state through to the solid-state phase transformations occurring at lower temperatures. This will be done by developing phase-field models that can deal with displacive transformations as well as diffusive, and SPH models with the ability to be coupled with thermodynamics.

Read more:

Arif TT, Qin RS, A phase-field model for bainitic transformation, Computational Materials Science, 2013, Vol:77, Pages: 230-235

Atomic Scale Theory and Simulation of High Temperature Shape-Memory Alloys

Researcher: Appala Naidu Gandhi
Supervisors: Professor Mike W Finnis and Dr David Dye
Sponsor: UKIERI, Imperial College

NiTi-based alloys are the most widely used for their shape-memory properties. These materials have a variety of specialised applications in such diverse fields as dentistry, medicine, and the aerospace industry. Our aim is to develop a theoretical understanding of how to control the temperature of their phase transition by additions of other elements to the basic alloy. The student would use a density functional method for calculating the total energy and phonon frequencies of a number of candidate materials for high temperature shape memory alloys based on NiAl. The energy of plausible crystal structures would be calculated at absolute zero to establish that the model indeed predicts the observed low temperature phase as the most stable, then from the phonon spectra, free energies in the quasiharmonic approximation can be calculated. This will enable phonon frequencies and elastic constants to be calculated as a function of temperature, and any signs of softening, the precursors to a phase transition, will be identified. The systematic effect of additions of impurities such as Pd, Pt, Fe, Cr, Zr and Hf to NiTi alloys are being studied, to elucidate the effect of atomic size, electronic structure and magnetism on the phase transition temperature.

Beta titanium at elevated temperatures

Investigator: Dr James Coakley

Supervisor: Dr David Dye

Collaborators: Dr John Webster, Rolls-Royce plc

Duration: 24/10/2011 - 23/5/2014 (PDRA)

Description:We are developing an understanding of superelastic beta titanium alloys for gas turbine applications. These alloys show remarkable non-linear elastic behaviour, with a very low stiffness and hysteresis in the loading-unloading cycle. Adapting these alloys from more traditional biomedical applications for use in aerospace requires greater knowledge of their performance at elevated temperatures. One focus has been the development of small angle neutron scattering (SANS) for the statistical characterisation of the evolution of 3-50nm precipitates in these alloys, as a complementary technique to 3D atom probe tomography

Calculating Liquid State Thermophysical Properties from First Principles

Researcher: Stefano Angioletti-Uberti
Supervisors: Professor Peter D Lee and Professor Mike W Finnis
Sponsor: EPSRC (Project Studentship)

This is part of a larger project developing an integrated multiscale modelling framework over the atomistic, defect and continuum length scales relevant to materials with heterogeneous microstructures. Working with researchers at Oxford, Cambridge, Birmingham and the industrial collaborators of Rolls-Royce and Siemens, this project is predicting: liquid state diffusion coefficients and solid-liquid interfacial energies from linked ab initio and molecular dynamics calculations, which will be used to simulate crystal formation during solidification, predicting microstructure, phase and composition using in-house microstructural modelling techniques. The models developed are being coupled into micromechanics models but experimental validation with existing data, and the design of new experiments is a key aspect. The final goal of the overall project is to open up as yet unexplored avenues in materials engineering, leading to true computational materials design

 

Calculating Liquid State Thermophysical Properties from First Principles

Researcher: Stefano Angioletti-Uberti
Supervisors: Professor Peter D Lee and Professor Mike W Finnis
Sponsor: EPSRC (Project Studentship)

Modern day single crystal Ni-base superalloy turbine blades suffer from defects arising during solidification (e.g., freckles). These defects may cause premature failure of the blade during service, thus the defective piece must be remelted increasing production costs. Freckle formation depends on preferential partitioning of elements during the solidification process; therefore a knowledge of the partition coefficients is required to engineer alloy compositions and casting procedure to avoid defect formation. Calculation of partition coefficients is possible using atomistic modelling and statistical mechanics. However, the accuracy of the calculated value depends on the reliability of the energetic description of the alloy, and ab-initio modelling is thus the best candidate for this purpose. Lower level approaches based on empirical potentials would be much faster due to their lower computational cost, but do not have the same accuracy. We show here that it is possible to combine both strengths of the two modelling approaches to calculate partition coefficients with an ab-initio accuracy in an efficient way by a free energy perturbation approach. The simulations, made using different embedded atom method potentials, show that it should be effectively possible to apply our technique to ab-initio calculations. This procedure will be applied to actual ab-initio calculations in the near future.

Patrick Burr - Atomistic modelling of Zr and Be intermetallics

Investigator: Patrick A Burr

Supervisors: Professor Robin Grimes and Dr Mark Wenman

Collaborators: Australian Nuclear Science and Technology Organisation (ANSTO)

Duration: 01/04/2012 - 01/05/2015 (PhD Studentship - ANSTO and EPSRC)

Description:The project investigates by means of atomic scale modelling, the role of intermetallic second phase particles found in Zr and Be alloys. Zr is used as nuclear fuel cladding in water cooled nuclear fission reactors, while Be alloys have been adopted as plasma facing material in current and future fusion tokamak reactors, as well as high-speed aerospace applications. In particular, the interaction of the intermetallic with H, He, and other impurities is investigated, as these degrade the performance of the alloy. Ultimately the aim is to predict new improved alloys with greater safety margins and longer life cycles.

Read more:

  • P.A. Burr, S.T. Murphy, S.C. Lumley, M.R. Wenman, R.W. Grimes, Corrosion Science 69 (2013) 1–4.
  • P. A. Burr, S.T. Murphy, S.C. Lumley, M.R. Wenman, R.W. Grimes, Journal of Nuclear Materials (2013), in press.

 

First author publications:

1. Burr PA, Wenman MR, Gault B, et al. From solid solution to cluster formation of Fe and Cr in α-Zr. Submitt to Acta Mater. 2015.

2. Burr PA, Middleburgh SC, Grimes RW. Crystal structure, thermodynamics, magnetics and disorder properties of Be–Fe–Al intermetallics. J Alloys Compd. 2015;639:111–122. doi:10.1016/j.jallcom.2015.03.101.

3. Burr PA, Murphy ST, Lumley SC, Wenman MR, Grimes RW. Hydrogen accommodation in Zr second phase particles: Implications for H pick-up and hydriding of Zircaloy-2 and Zircaloy-4. Corros Sci. 2013;69:1–4. doi:10.1016/j.corsci.2012.11.036.

4. Burr PA, Murphy ST, Lumley SC, Wenman MR, Grimes RW. Hydrogen solubility in zirconium intermetallic second phase particles. J Nucl Mater. 2013;443(1-3):502–506. doi:10.1016/j.jnucmat.2013.07.060.

Other publications:

5.  Horlait D, Grasso S, Al Nasiri N, Burr Pa, Lee, We. Synthesis and oxidation testing of MAX phases composites in the Cr-Ti-Al-C quaternary system, J Am Ceram Soc. In press.

6. Lumley SC, Murphy ST, Burr PA, Grimes RW, Chard-Tuckey PR, Wenman MR. The stability of alloying additions in Zirconium. J Nucl Mater. 2013;437(1-3):122–129. doi:10.1016/j.jnucmat.2013.01.335.

7. Middleburgh SC, Karatchevtseva I, Kennedy BJ, et al. Peroxide defect formation in zirconate perovskites. J Mater Chem A. 2014;2(38):15885–15888. doi:10.1039/C4TA02558J.

8. Lumley SC, Grimes RW, Murphy ST, et al. The thermodynamics of hydride precipitation: The importance of entropy, enthalpy and disorder. Acta Mater. 2014;79:351–362. doi:10.1016/j.actamat.2014.07.019.

9. Middleburgh SC, Burr P a., King DJM, Edwards L, Lumpkin GR, Grimes RW. Structural stability and fission product behaviour in U3Si. J Nucl Mater. 2015. doi:10.1016/j.jnucmat.2015.04.052.

Non peer-reviewed:

10. Rushton MJD, Wenman MR, Mella R, Burr PA. Providing skilled graduates to the nuclear industry. Nucl Futur. 2013;9(1):44.

 

Characterise and model a gamma/gamma prime microstructure in a nickel-based superalloy

Investigator: Dr Gaofeng Tian

Supervisor: Dr Barbara Shollock and Professor Fionn Dunne

Collaborators: Dr Jun Jiang

Duration:01/05/2013 - 30/04/2015

Description: Gamma prime precipitates are important strengthening phase in nickel-based superalloy, its microstructural characteristics has an important influence on the mechanical properties. The main aim of the project is to investigate the evolution of gamma prime microstructures or gamma/gamma prime micromechanical properties in the alloy under the different heat treatment conditions and develop models for mechanical behaviour of the evolving gamma prime precipitates in service.

Tamara Chapman - Fatigue cracking behaviour in Ti-6Al-2Sn-4Zr-6Mo

Investigator: Tamara Chapman

Supervisors: Dr David Dye and Professor Trevor Lindley

Collaborators: Dr. Adrian Walker, Prof. David Rugg and Dr Edward Saunders, Rolls-Royce plc

Duration: 01/10/2011 - 30/9/2014 (PhD Studentship)

Description:The occurrence of low life surface initiated fatigue cracks in Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) associated with the presence of Cl is investigated. These cracks are typically recognised by the presence of characteristic fractographic discolouration and local variance of fractographic topography. Secondary Ion Mass Spectrometry has been used to identify the characteristic chemical footprint, along with SEM and TEM based EDX. In addition, transmission electron microscopy on samples rem o ved by FIB milling is used to identif y the micro-mechanisms associated with crack initiation.

Combinatorial Development of High Temperature Shape Memory Alloys

Researcher: Mohammed Abdul Azeem
Supervisors: Dr David Dye, Dr Richard J Dashwood and Professor Trevor C Lindley
Funding: UKIERI, Imperial College

Shape memory alloys (SMAs) have great potential to replace conventional electro-mechanical and hydraulic actuators in a broad range of applications, particularly in gas turbines. However, the temperature range of the transformations is currently quite restricted and it is of interest to develop SMAs with higher transformation temperatures. In this project, we are collaborating with the Indian Institute of Science, Bangalore to use the combinatorial approach to test a broad range of compositions using synchrotron diffraction and diffusion multiples. In addition, micromechanical and atomistic modelling will be used to develop insight into the alloy design and into the underlying science of the transformations, which are not well understood.

Mitch Cuddihy - Cold dwell crack nucleation in titanium aeroengine components

Investigator: Mitch Cuddihy

Supervisors: Professor Fionn Dunne and Dr Daniel Ballint (Mech Eng)

Collaborators: Dr. Adrian Walker, Dr. David Rugg, Rolls-Royce plc

Duration: 10/01/2012 - 30/9/2015 (PhD Studentship)

Description:This research seeks to contribute to the understanding of cold dwell fatigue, an area of critical importance to the aerospace industry due to its impacts on both component lifespan and efficiency. Cold dwell facet fatigue is a significant and problematic failure mode exhibited by certain titanium alloys that are used in key areas of the gas turbine used in aerospace engines. Current work centres on the development of a crystal plasticity finite element model which will be used to inves tigate the eff ects of factors such as macrozone size and porosities near grain boundaries.

Creep Modelling in Polycrystal Nickel Superalloys

Researcher: James Coakley
Supervisors: Dr David Dye and Professor Roger Reed (University of Birmingham)
Sponsors: EPSRC (Industrial Case Studentship), QinetiQ

The aim of the programme is to extend the existing McLean-Dyson-Basoalto creep model to yield an improved treatment in the case of polycrystal nickel superalloy disc alloys. Specifically we wish to account for 1) the effect of multi-modal gamma prime, 2) the effect of misfit stresses and their evolution, 3) a mapping through to athermal yield, so that high stresses can be considered and a consistent approach taken to normal tensile testing, and 4) the effect of grain size. Specialist testing, potentially including synchrotron and/or neutron diffraction, will also be undertaken to validate the relationships proposed.

Bernadette Elliott-Bowman - Thermomechanical processing of high carbon steel

Investigator: Bernadette Elliott-Bowman

Supervisors: Dr Rongshan Qin

Duration: 01/09/2012 - 31/05/2015 (PhD Studentship)

Description:This project aims to optimise thermomechanical processing methods for the manipulation of microstructure in high carbon steel. The effects of processing on grain size, recrystallisation rate and associated mechanical properties are considered. Deformation and heat treatment of samples is carried out using in-house equipment. Microstructure characterisation is achieved through the use of SEM, TEM, EBSD and FIB analysis. Mechanical properties including Vicker’s hardness, tensile strength and electrical resistivity are also assessed. Ultimately, the information gathered will be used to understand and develop the relationship between processing, microstructure and mechanical properties.

Defect Formation in Single Crystal Nickel-based Superalloys

Researcher: Dylan Ness
Supervisor: Professor Peter D Lee
Sponsor: EPSRC (Project Studentship)

This project is part of a larger US-UK collaborative project whose overall aim is to understand and quantify the factors leading to the formation various solidification defects in nickel-base superalloys. This project focuses on the measurement of the critical material properties for compositions corresponding to the melting range of the alloys. This information will be incorporated in numerical models of defect formation and coupled with macroscopic process models to provide guidance on process control to minimise defect formation. This will centre on the latter aspects, specifically the multiscale modelling of investment casting:

  1. Quantifying and developing appropriate microstructural models that account for the defect formation.
  2. Integrating these micro-models with macro-process models (e.g., shaped castings, liquid metal processing).
  3. Quantification of the models and validation of the findings through laboratory, pilot and industrial-scale experiments.

Tomiwa Erinosho - Strain path effects in ferritic steel polycrystals

Investigator: Tomiwa Erinosho

Supervisor:  Professor Fionn Dunne

Collaborators: Prof A Wilkinson, Prof R Todd, Prof A Cocks and Dr D Collins (University of Oxford) and BMW

Duration: 9/1/2012 - 9/1/2014 (PhD Studentship)

Description:There is evidence to show that biaxially straining steel non-proportionally can result in higher limit strains or conversely, premature failure depending on the strain path followed. Thus, it is imperative to understand the concept of non-proportionality, its relationship with texture and industrially important effects such as material localization and consequent failure in forming processes for high strength steels applied in auto components.

Read more:

Erinsho, T.O. and F.P.E. Dunne, Lattice strain distributions due to elastic distortions and GND development in polycrystals. Journal of the Mechanics and Pysics of Solids. 67(0): p 62-86 (2014)

Erinosho, T.O., A.C.F. Cocks, and F.P.E. Dunne, Texture, hardening and non-proportionality of strain in BCC polycrystal deformation. International Journal of Plasticity. 50(0): p. 170-192. (2013)

Erinosho, T.O., A.C.F. Cocks, and F.P.E. Dunne, Coupled effects of texture, hardening and non-proportionality of strain on ductility in ferritic steel. Computational Materials Science. 80(0): p. 113-122 (2012)

Erinosho, T.O., A.C.F. Cocks, and F.P.E. Dunne, Non-Proportionality of Strain And Coupling Effects on Dislocation Distribution and Ductility in Ferritic Steel Polycrystal. Coupled Problems V (conference proceedings). (2012)

Deformation of Dendritic Structures in Directionally Solidified Al-Cu Alloys

Researcher: Devashish Fuloria
Supervisor: Professor Peter D Lee
Sponsor: Alcoa Incorporated

Aluminium has now exceeded steel in usage in automobiles due to its lightweight and hence improved mileage. However, despite the reduced environmental impact during use, the production of aluminium sheet is both costly and energy intensive. Twin roll casting is a method of directly producing aluminium alloys in near net shape to sheet at a fraction of the energy costs of conventional DC casting/hot rolling. It also requires a fraction of the capital cost. Although sheet can be produced, various defects can arise which limit the range of alloys which can be cast. This project hopes to elucidate the complex mechanisms causing these defects through a combined experimental and computational study. The overall aim of the project is to gain an improved understanding of the deformation of aluminium alloys during their solidification.

Peter Evans - TWIP beta-Ti armour and containment alloys

Investigator:Peter J. Evans

Supervisor: Dr David Dye

Collaborators: Dr Matthew Thomas and Mr Roger Thomas, TIMET

Duration: 01/10/2012 - 01/10/2015 (PhD Studentship)

Description: Twinning-induced plasticity (TWIP) has been identified as an effective means of improving the strain-hardening rate of beta titanium alloys, making them suitable for applications requiring a high energy-absorptive capacity, such as fan-blade containment and armour. We will optimise these properties under both static and high strain-rate impact conditions, relating composition and phase stability to the mechanical response of metastable beta alloys.

Effect of Texture on Performance of Ti-6Al-4V

Researcher: Ioannis Bantounas
Supervisors: Dr David Dye and Professor Trevor C Lindley
Sponsor: EPSRC (Project Studentship)

Current developments in thermo-mechanical processing and novel production routes (e.g., electrolytic reduction) offer the opportunity to provide step-change improvements in the performance of advanced materials. However, new alloy and process developments traditionally have taken 10-15 years to deliver into service, which inhibits the adoption of new technologies. Advances in materials modelling offer the possibility of drastically reducing this lead time through the adoption of virtual prototyping applied to qualification testing and for the optimization of processing. The programme is aimed at 1) investigating whether the effect of texture on fatigue performance is mediated by intergranular microstrains or by some other mechanism, 2) predicting the effect of texture on intergranular microstrain accumulation in this system, 3) predicting the extures obtained during deformation processing and 4) deriving a physically reasonable model for the effect of microstrains on fatigue performance. This would then enable the optimisation by deformation processing of the fatigue performance of Ti-6Al-4V components using knowledge of the in-service loading conditions.

Electrochemical Deoxidation of Titania-based Mixed Metal Oxides

Researcher: Rohit Bhagat
Supervisors: Dr Richard J Dashwood, Dr Martin Jackson and Professor Douglas Inman
Sponsor: Defence Advanced Research Projects Agency DARPA)

The Fray-Farthing-Chen (FFC) Cambridge process was initially developed to reduce titanium dioxide directly in molten calcium chloride. It has subsequently been used to produce several other metals and alloys via the reduction of their respective oxides. In the current work the potential of the process to produce titanium based alloys with compositions that are difficult to synthesize conventionally (i.e., Ti-W) is being assessed. Electrochemical predominance diagrams are being used to predict the stable compounds produced during the reduction of mixed oxides and the reduction pathway is being investigated using a series of partial reductions. Initial experiments have shown that reduction entails interaction between the various metal oxides and sub-oxides, solid state diffusion of metallic components and, in some cases, chemical reactions with the molten salt. In all the alloys investigated chemical homogeneity is achieved during reduction even in notoriously slow diffusing systems such as Ti-W. It is postulated that this homogenisation takes place in the oxide phases where diffusion of the solute species is greater than in metallic titanium.

Electrochemical Reduction of TiO2 in Molten CaCl2

Researcher: Kartik Rao
Supervisors: Dr Richard J Dashwood and Professor Douglas Inman
Sponsor: EPSRC (DTA)

This project concerns the study of lower titanium oxides and calcium titanates during electrochemical reduction in molten salt. The oxides and titanates are of special interest owing to their role as reaction intermediaries in the Fray-Farthing-Chen (FFC) process. For the purpose of this study, the lower oxides and titanates are defined as compounds where titanium exists in a lower oxidation state than 4+. While existing work has demonstrated the existence of these phases during the reduction process, several different oxides may coexist together, thus in-situ studies typically deal with composite material. Using homogeneous precursor material, evaluation of individual reduction reactions is possible. The overall aim of this study is to evaluate the reduction process to quantify the relationship between precursor material and reduction parameters. To achieve this goal, the following objectives are targeted: 1) Optimise precursor production to replicate in-situ morphology and chemistry and obtain material of controlled porosity. 2) Develop understanding of reduction mechanisms and sequences

Dr Jun Jiang - Micro-mechanical tests in aerospace materials

Investigator: Dr Jun Jiang

Supervisor:  Professor Fionn Dunne and Dr T Ben Britton

Collaborators: Dr Gaofeng Tian (Aviation Industry Corporation of China) and Prof A Wilkinson (Oxford)

Duration: 7/1/2013 - 7/1/2015 (PDRA)

Description: This project addresses crack nucleation in aerospace alloys under fatigue and creep failure modes. Deformed samples will be characterised using High Resolution EBSD and deformation patterning and crack imitation sites will be linked to microstructure through microstructurally faithful and physically reasonable finite element models.

Read more:

J Jiang, TB Briton, AJ Wilkinson, Evolution of dislocation density distributions in Copper during tensile deformation, Acta Materialia (2013)

J Jiang, TB Briton, AJ Wilkinson, Mapping type III intragranular residual stress distributions in deformed copper polycrystals, Acta Materialia (2013)

TB Briton, J Jiang, PS Karamched, AJ Wilkinson, Probing Deformation and Revealing Microstructural Mechanisms with Cross-Correlation-Based, High-Resolution Electron Backscatter Diffraction, JOM (2013)

 

Extrusion of Zr-2.5Nb for Pressure Tube Applications

Researcher: Konstantinos Alevizos
Supervisors:Dr David Dye, Dr Richard J Dashwood and Dr Martin Jackson
Sponsor: European Union Marie Curie Fellowship

The creep performance of Zr-2.5Nb is a sensitive function of both its texture and microstructure. In this project, model extrusions of Zr-2.5Nb are being performed with the aim of optimising the texture and microstructure to maximise creep performance. An auxilliary programme of Al tube extrusions and isothermal compression testing will be performed. Finite element models will be used to predict the metal flow, adiabatic heating and strain path within the material, and these will be linked to models for the texture and microstructure development.

Dr Tea-Sung (Terry) Jun - Micromechanics of hexagonal polycrystals

Investigator: Dr Tea-Sung (Terry) Jun

Supervisors: Dr Ben Britton and Professor Fionn Dunne

Collaborators: Rolls-Royce plc/Timet/Westinghouse/EDF

Duration: 13/01/2014 - 13/01/2016 (PDRA - HexMat)

Description: We will investigate micro-mechanical deformation mechanism of hexagonal polycrystals. These alloys are profoundly important to industries (aero, energy, biomedical, defence sector, etc) for improving our daily-lives. Hexagonal materials have complex internal structures, and hence require detailed experimental characterisation, theoretical description and appropriate prediction models. Samples will be deformed by micro-mechanical testings (e.g., micro-pillar or micro-cantilever) and simultaneously characterised by in-situ EBSD and DIC. Based on the experimentally-obtained deformation behaviour linked to microstructural changes, finite element models will be developed
and compared.

Fatigue Initiation and Micromechanics of Ti-6Al-4V

Researcher: Adam M Stapleton
Supervisors: Dr David Dye, Dr Richard J Dashwood and Professor Trevor C Lindley
Sponsors: EPSRC, Rolls-Royce plc

It is thought that crystallographic texture plays a crucial role in mediating the fatigue behaviour of Ti-6Al-4V, possibly through the effects of intergranular microstrain. The project is investigating the way in which load is partitioned between particular orientations and phases during cyclic tensile loading using X-ray and neutron diffraction. An elasto-plastic self consistent (EPSC) model, based upon the notion of an ellipsoidal inclusion interacting with a surrounding homogeneous effective medium (HEM), provides a mathematically rigorous basis for the simulation of mechanical loading in polycrystalline materials. This is used to predict the behaviour and evolution of intergranular microstrains in a polycrystalline material during cyclic loading.

Kristina Kareh - In situ synchrotron tomography of granular deformation in semi-solid Al-Cu alloys

Investigator: Kristina Kareh

Supervisors: Dr. Chris Gourlay and Professor Peter Lee (Manchester)

Collaborators: Dr. R. Atwood (Diamond Synchrotron)

Duration: 1/10/2009 - 30/9/2013 (PhD Studentship)

Description:Mounting evidence points towards metals behaving as cohesionless granular materials when deformed in the semi-solid state, which can lead to large-scale defects due to shear banding in components deformed during solidification. Using fast synchrotron X-ray tomography, the microstructure of globular binary Al-Cu alloys has been imaged during uniaxial compression and extrusion in 3D. By characterising the shape of all crystals i n the specimen, their displacements and interactions are being tracked during deformation with the aim of better understanding mush rheology.

Read more:

K.M. Kareh, P.D. Lee, and C.M. Gourlay. Globule-globule interactions during deformation in semi-solid Al-Cu using time-resolved X-ray tomography. 12th International Conference on Semi-Solid Processing of Alloys and Composites (S2P XII), Cape Town, South Africa 2012.

K.M. Kareh, P.D. Lee, and C.M. Gourlay. In situ, time-resolved tomography for validating models of deformation in semi-solid alloys. 13th Modeling of Casting, Welding and Advanced Solidification Processes 2012‎ (MCWASP XIII), Schladming, Austria 2012.

In situ synchrotron characterisation of Fe-rich intermetallic formation during the solidification of Al-Si-Cu-Fe alloys

Investigator: Chedtha Puncreobutr

Supervisors: Professor Peter Lee (University of Manchester) and Dr Andrew Horsfield

Duration: 01/10/2009 - 30/09/2013 (PhD Studentship)

Collaborators: T. Connolley (DLS), J.L. Fife (SLS), A.B. Phillion (UBC)

(a) Al-Si-Cu-Fe solidifying microstructure; (b) intermetallics (coloured) and dendrites (light grey) rendered in 3D from an ROI [yellow square in (a)]; (c) CFD simulated velocity field showing how intermetallics block liquid flow.
(a) Al-Si-Cu-Fe solidifying microstructure; (b) intermetallics (coloured) and dendrites (light grey) rendered in 3D from an ROI [yellow square in (a)]; (c) CFD simulated velocity field showing how intermetallics block liquid flow.

Description:The enrichment of Fe during aluminium recycling enhances the formation of Fe-rich intermetallics, particularly β-Al5FeSi, limiting their usage in many fatigue-sensitive applications. In this project, fast synchrotron x-ray tomography is used to investigate microstructure evolution and defect formation in a commercial Al-Si-Cu-Fe alloy. Novel image analysis techniques as well as coupled computational fluid dynamics provide new insights into the mechanisms of intermetallic nucleation and growth, together with their influence on defect formation. This characterisation of dynamic behaviour then helps design better alloys and applications.

Read more:

C. Puncreobutr, P.D. Lee, R.W. Hamilton, B. Cai, T. Connolley, Synchrotron tomographic characterisation of damage evolution during aluminium alloy solidification. Metallurgical and Materials Transactions A, Online First, 2012.

C. Puncreobutr, P.D. Lee, R.W. Hamilton, A.B. Phillion, Quantitative 3D characterisation of solidification structure and defect evolution in Al alloys. JOM, 64(1), pp.89-95, 2012.

Investigation of the effect of lanthanum on the oxidation of CMSX-4

Investigator: Jinesung Jung

Fractured oxide scale micrographs acquired on the side plane of sample: (a) CMSX-4 9624 and (b) CMSX-4 (La) -9624.
Fractured oxide scale micrographs acquired on the side plane of sample: (a) CMSX-4 9624 and (b) CMSX-4 (La) -9624.

Supervisors: Dr. Barbara Shollock and Dr David McPhail

Duration: 01/03/2010 - 31/12/2013 (PhD Studentship)

Description:Single-crystal nickel-base suepralloys are extensively used for blades with thermal barrier coating (TBC) system in gas turbine engine. In the case of the coating failure in service, substrate is directly exposed to corrosive gas environment and is damaged by oxidation. Understanding the oxidation behaviour of bare metal is crucial to improve the performance of the single-crystal nickel-base superalloys. This research focuses on elucidating high temperature oxidation behaviour of CMSX-4 alloy with the doping of lanthanum including the transient oxidation behaviour during heating up with oxygen partial pressure. To do this, two-stage oxidation experiments using isotopic oxygen have been performed and various analyzing methods such as FEG-SEM, TEM with EDX, FIB-SEM, and ToF-SIMS have been applied.

Matthias Knop - Deformation behaviour of Co-base superalloys

Investigator: Matthias Knop

Supervisor: Dr David Dye

Collaborators: Rolls Royce plc

Duration: 04/07/2011 - 03/07/2014 (PhD Studentship)

Description: The aim of this project is to find an alternative to the established Ni-base superalloys for the hot section of turbine engines. Co-base alloys may be an suitable alternative because of their higher melting point and better corrosion resistance. This leads to an increase of the service temperature to increase the fuel efficiency and therefore reducing cost and CO2-emissions. In 2006, Sato et al. discovered a phase in Co-base alloys which improves their high temperature strength significantly. Alloy candidates with a desired microstructure and oxidation resistance will be developed and mechanically tested to evaluate their viability.

Microstructural Investigation of Nickel-based Superalloys

Researcher: Despina Hadjiapostolidou
Supervisor: Dr Barbara A Shollock
Sponsors: EPSRC (Responsive Mode Studentship), Rolls-Royce plc, RWE NPower

The nickel-base superalloys used in gas turbines face one of the most challenging conditions of any material. Used at high temperatures and stresses, these alloys must maintain their strength despite microstructural changes. The mechanical properties of these alloys are determined by the precipitation of γ' phase in the γ matrix; the properties are affected by the size, shape and distribution of these γ' precipitates. This project investigates the effect of long-term aging (up to 20,000 hours, 800C to 1050C) on the coarsening of γ' precipitates in René 80, a polycrystalline Ni-base cast superalloy. Long term exposure is especially important for gas turbines used in the power generation industry as these turbines operate continuously for extended periods. It has been found that coarsening continues even after long term exposure, contrary to the popularly accepted idea that coarsening does not continue past about 1000h.

The oxidation and nitridation of the material after long term aging is being investigated. After long times at temperature, significant degradation of the surface and subsurface of the alloy occurs by internal nitridation and oxidation. TEM and XRD have been used to identify the complex phase formed and a model for the process is being developed.

Modelling the Melt and Mreeze Behaviour of Materials for the Next Generation of High

Researcher: Zohaib Malik
Supervisors: Professor Peter D Lee and Dr R Lowe (National Physical Laboratory)
Funding: EPSRC (Industrial Case), NPL

This project is explaining the melt behaviour of metal-carbon binary eutectic alloys with melt temperatures up to 2500C. These alloys are attracting increasing interest as reference standards based on their eutectic temperature. It is expected they will be formally accepted as standards following the proposed redefinition of the kelvin in ~2012. We are applying and developing of improved macroscopic and microscopic models of diffusion in eutectic alloys. These are being validated against experimental melt data and assessed microstructure. The relative importance of microstructure, impurities and thermal environment will be assessed.

Multiscale Modelling of Continuous Casting Processes

Researcher: Pavel E Ramirez Lopez
Supervisors: Professor Peter D Lee and Professor Kenneth C Mills
Sponsor: National Council of Science and Technology (CONACYT), Mexico

Quality control of the Continuous Casting Machine is difficult due to the variety of physical phenomena occurring simultaneously in the casting process. These phenomena include heat transfer, metal flow dynamics and solidification. The combination of all these factors produces a complex process where the alteration of one variable has deep impact in the rest and finally, in the quality of the product. This project is gaining an understanding of the physical phenomena taking place inside the mould. Therefore, the effects of the principal casting variables in the whole process are analysed and quantified. Once these fundamentals are fully understood, it is possible to predict optimal casting conditions for a defect free practice. The analysis is based on a numerical model capable of coupling metal flow dynamics, heat transfer and solidification inside the mould. The multiphase system (molten steel-slag-air-argon) and the stress accumulation in the shell are being modelled to provide a realistic representation of the process. Slag composition and physical properties are also included to determine their influence on lubrication and defect formation.

New Materials for Long Life Flare Tips

Researcher: Sobhan Abolghasemi
Supervisors: Professor Peter D Lee and Professor Trevor Lindley
Sponsor: EPSRC (DTA)

Flare tips are part of an oil and gas platform's essential safety system, allowing for the safe disposal of hydrocarbons in the event of an emergency. Flare systems are increasingly operated at low gas flow rates to meet environmental regulations; an operating regime that increases the time that the flame impinges on the tip, thus increasing its operating temperature and decreasing the lifetime. Extending flare tip life will have a significant impact on both safety and maintenance costs. A potential failure involves a material degradation process based on a high temperature creep-fatigue-oxidation interactive mechanism which is thought to promote local grain boundary embrittlement of the metallic alloys. A Thermomechanical Index of alloy behaviour is being developed to optimise the selection of alloys for potential flare tip use. Flare tip metal temperaturesare measured using thermo-imaging techniques. Knowledge of the actual operating temperature range will allow a more robust analysis of the alloy behaviour by removing the simplifying assumptions that have been made to date. The thermo-mechanical models will be extended to include local embrittlement processes, including the role of oxidation behaviour (particularly at grain boundaries), processes that are presently poorly understood. The kinetics of high temperature oxidation of Inconel 625, the 700 series and other alloys designed for high temperature oxidation resistance will be studied using optical and electron microscopic techniques. An understanding the materials issues involved and a development of improved solutions will enable platform operators to develop a risk-based inspection strategy for flare tips.

Wenjun Lu - Microstructure processing for steels

Investigator: Wenjun Lu

Supervisors: Dr Rongshan Qin and Professor Jianguo Lin (Mech Eng)

Duration: 01/10/2012 - 30/09/2015 (PhD Studentship)

Description: Processing conditions are designed for fabrication of novel microstructures. Thermodynamics, kinetics for phase transition and heat/mass transfers are considered. Optical microscope, SEM, EBSD, XRD are applied to characterize the microstructures. Mechanical properties (e.g. Vickers hardness, tensile strength, ...) of the samples are measured. Several steels are examined to provide the design principles.

Oxidation and oxygen transport in a commercial polycrystalline Ni-based superalloy under static and loading conditions

Investigator: Benjamin Foss

Supervisors: Dr. David McPhail and Dr. Barbara Shollock

Duration: 01/10/2010 - 01/11/2013 (PhD Studentship - EPSRC/Rolls-Royce plc)

Collaborators: Rolls-Royce plc

Description:The current demands of the aviation industry for increased gas-turbine efficiency pushes Ni-based superalloys used for turbine discs to their operational limits. Throughout the disc’s service life, it is important that the mechanical integrity is maintained. This drive for improved efficiency necessitates higher turbine entry temperatures, requiring that alloys used exhibit superior oxidation resistance. The synergistic effects of oxidation and high mechanical stresses pose an even greater problem and can be responsible for a reduction in the fatigue life of these components. My work investigates the role of oxidation and oxygen transport during high-temperature exposure of an advanced powder metallurgy Ni-based superalloy currently used in the latest of gas turbines. Specifically, experiments have developed and adopted the use of isotopic tracing protocols in combination with Focused Ion Beam Secondary Ion Mass Spectrometry (FIB-SIMS) to characterise oxygen transport. In contrast to conventional SIMS by either mass spectrometry or depth profiling, FIB-SIMS offers the opportunity to produce elemental maps with excellent lateral resolution.

Read more:

B. J. Foss, S. Gray, M.C. Hardy, S. Stekovic, D. S. McPhail, B. A. Shollock,; Analysis of shot-­‐peening and residual stress relaxation in the nickel-­‐based superalloy RR1000.; Acta Materialia, 61, 7, 2458-­‐2559 (2013).

Simulation of the Mechanical and Flow Behaviour of Bone Fixation Implants

Investigator: Ziyu (Flora) Zhang

Supervisors: Dr Julian Jones and Prof Peter Lee (Manchester)

Duration: 01/10/2009 - 01/08/2013 (PhD Studentship)

Collaborators: Stryker Orthopaedics

Description:Titanium (Ti) porous foams produced by additive manufacturing (AM) techniques are promising for fixation devices in orthopaedic applications. These implants should possess sufficient permeability to allow vascular invasion, integration with the host tissue and also satisfy the transport requirements of remodelling bone. The mechanical properties of implants should also match those of the host tissue to ensure sufficient life span in the body. Both macro and micro-structures of implants influence the mechanical and flow properties. Techniques are therefore needed to characterise the structural parameters and to evaluate their effects on the performance of the implant. This project focuses on computational modelling tools based on X-ray microtomography (µCT) images to characterise the flow and mechanical properties of porous foams. The aim of the study is to develop and apply these tools on Ti implants with different structures to investigate how the design variables offered by AM technique can be used to alter the implant architecture on multiple length scales to control and tailor the flow and mechanical properties.

Read more:

Zhang, Z., Jones, D., Yue, S., Lee, P.D., Jones, J.R., Sutcliffe,, C.J., Jones, E., “Hierarchical tailoring of strut architecture to control permeability of additive manufactured titanium implants”, Mat. Sci. Eng. C, 33 (7), pp4055–62, 2013

Paul Mulvey - Development of Co-based superalloys

Investigator: Paul Mulvey

Supervisor : Dr David Dye

Duration: 01/07/2013 - 30/06/2016 (PhD Studentship - EPSRC)

Collaborators: Rolls Royce plc.

Description: Next generation superalloys based on the Co-Al-W system are being developed to produce strong, oxidation resistant alloys to replace the out-dated Ni-based superalloys currently used in gas turbine applications. Co-based alloys have the potential to offer superior corrosion resistance and higher melting points compared to the current Ni-based alloys, resulting in the ability to design higher turbine entry temperatures. This project will investigate the new ternary Co3(Al,W) phase, its deformation mechanisms and the effects of heat treatment on the microstructure, with particular focus on the role of carbide formation. Analysis techniques will include TEM, FIB, EBSD and synchrotron X-ray diffraction.

Stress Corrosion Cracking of Metal Packaging for Foods

Researcher: Peter J Smith
Supervisors: Professor Alan Atkinson and Professor MG (Gwyn) Hocking
Sponsors: Crown Technology, Wantage (PRI Scheme)

During the past 15 years the processed food can sector of the Metal Packaging Industry has experienced a significant incidence of environmental stress cracking failures in metal containers having either tinplate or electro chrome coated steel components. The time to failure has varied significantly from less than one year following packing to three years or more. Despite investigations by can makers and steel suppliers, published work does not provide a comprehensive understanding of the problem to enable preventative measures to be implemented, which are both effective and economic. The present study is gaining a better understanding of risk factors and potential means to reduce risks. Two main container types are being examined: three-piece round and two-piece drawn and redrawn containers. Both container types show susceptibility to environmental stress cracking failures at the more heavily worked areas of the bodies and or ends.

Dr Maelig Ollivier - Influence of contact reactions and thermal treatments on the surface of pure silver

Investigator: Dr Maelig Ollivier

Supervisors: Dr Chris Gourlay

Collaborators: AWE

Duration: 01/02/2014 - 31/1/2016 

Description: If heated to high temperatures, silver surfaces undergo pronounced morphological surface changes: a process known as "thermal etching" which includes surface roughening, the formation of striations, faceting, grooving and etch pitting. These different phenomena are influenced by a large set of parameters, such as temperature, time, the atmosphere surrounding silver or contact material and contact pressure. The aim of this project is to better understand the formation of sub-micron to micron sized features on the surface of silver and to study the link between the surface changes and the extrinsic parameters applied to the material.

Superelastic beta titanium

Investigator: Oliver Joris

Supervisor: Dr David Dye

Collaborators: Dr. Adrian Walker, Prof. David Rugg and Dr Edward Saunders, Rolls-Royce plc

Duration: 1/9/2010 - 23/12/2013 (PhD Studentship)

Description:Beta titanium alloys can be used in both biomedical and energy absorption applications due to their low modulus and energy absorption capabilities. Key to this is the superelastic property, where there is a stress induced fully recoverable phase transformation. In this work, we are examining the effect of beta stability (Mo and Al content) and O content (stress to induce the phase transformation and reversibility). We will use a variety of techniques, including the high energy JEEP X-ray beamline at the Diamond Light Source. Here we are exploring the phase transformation using in-situ ther momechanical testing. This will be combined with laboratory studies, including T EM to study fine scale microstructure features and phases present.

Other projects

  • Fundamentals of Deformation and Cracking in Zirconium Alloys
  • Generation of Ultra-fine Grained Microstructures via Multiple Extrusions
  • Micromechanical Modelling of the Forging of Titanium Alloys
  • Micromechanics and Phase Transformations in Welded Steel Joints
  • Micromechanical Modelling of the Forging of Titanium Alloys
  • Micromechanics and Phase Transformations in Welded Steel Joints
  • Optimisation of the FFC Cambridge Process for Processing of NiTi
  • Porosity Formation in Aluminium Alloys: In-situ Observation and Mesoscale Simulation
  • Production and Charaterisation of Metal Foams
  • TBC Surface Chemical Contamination on Service-retrieved Industrial Gas Turbine Engines
  • Thermomechanical Processing of Near Beta Titanium Alloy 5al-5V-5Mo-3cr
  • Thermomechanical Processing of Titanium Matrix Composites
  • Ti-64 Deformation

Dr Daniela Proprentner - Oxidation damage at a crack tip and its significance in crack growth under fatigue-oxidation conditions

Investigator: Dr Daniela Proprentner

Supervisor: Dr Barbara Shollock

Duration: 06/20/2013 - 07/19/2015 (PDRA - EPSRC funded)

Collaborators: Loughborough University, University of Southampton, Alstom, DSTL, E.ON, NASA

Description: Nickel-based alloys are widely used in power generation, nuclear and aerospace industries due to their superior mechanical properties at high temperature. As structural materials these alloys require a strong resistance to crack initiation and propagation for safe-life design and assessment of their components. At elevated temperature crack growth rates in such alloys exposed to air can be drastically accelerated, by two and even three orders of magnitude, due to the attack of oxidation. This research will investigate the physical process of oxidation damage at a crack tip and crack growth providing direct insight into oxidation-embrittlement phenomenon at crack tip under fatigue-oxidation conditions in controlled environments (vacuum, air, oxygen-18).

Anna Radecka - Short-range ordering and the deformation mechanisms of Ti-7wt%Al

Investigator: Anna Radecka

Supervisor: Dr David Dye and Professor Trevor Lindley

Collaborators: Professor David Rugg, Rolls-Royce plc

Duration: 01/10/2012 - 30/09/2015 (PhD Studentship)

Description: It is well documented that cracks and defects develop under safe load, often as result of fatigue. A better understanding of the fatigue-cracking behaviour of titanium alloys is a key challenge if we are to ensure the long-term reliability of jet engine components. We need to develop an accurate method for the estimation of the fatigue life of a component and a necessary prerequisite will be to identify the plastic deformation process leading to fatigue cracking. The aim of the project is to determine how ordering of aluminium atoms can affect the extent of planar slip in alpha grains occurring during the plastic deformation in alpha-titanium alloys. The degree of planar slip can be linked to fatigue performance.

Alireza Rahnama - TMPC - Property relationships in strong steels

Investigator: Alireza Rahnama

Supervisors: Dr Rongshan Qin

Duration: 01/10/2010 - 01/10/2013 (PhD Studentship)

Description:This project is both computational and experimental in nature. A 3D model using a new computational method for phase transitions in the thermomechanical processing of strong steels has been developed. The model includes the thermomechanical processing conditions (TMPC) and property relationships of strong steels that will be applied in the automobile industry. In the experimental part, a novel microstructure in transformation-induced plasticity (TRIP) steel has been developed by the application of innovative electropulsing technique (EP). Mechanical properties and microstructure have been investigated by a number of techniques including optical microscope, TEM, XRD, SEM and mechanical testing.

Dr Ananthi Sankaran - Micro-mechanisms involved during high cycle fatigue of zirconium alloys

Investigator: Ananthi Sankaran

Supervisors: Dr David Dye

Collaborators: Rolls-Royce plc.

Duration: 27/10/2012 - 30/09/2014 (PDRA)

Description: The current research addresses the mechanisms responsible for the plastic deformation and cracking in Zircaloy-4. Zircaloy-4 is regularly used in pressurised water reactors. They are subjected to High Cycle Fatigue (HCP) as a result of fluctuating temperatures and vibrational loading in service. To address this problem HCF tests were performed on a recrystallised Zircaloy-4. A combination of Quantitative Tilt Fractography and Electron BackScatter Diffraction (EBSD) is used to determine the spatial and crystallographic orientation of the fracture facets at the initiation site. Transmission Electron Microscopy (TEM) is used to determine the deformation mechanisms and dislocation motions along specific slip systems.

Peter Tympel - The effect of complex loadi ng regimes on fatigue of Ti-6Al-4V

Investigator: Peter Tympel

Supervisor:  Dr. David Dye and Professor Trevor Lindley

Collaborators: Mark Dixon and Edward A Saunders, Rolls-Royce plc.

Duration: 01/10/2012 - 9/30/2015 (PhD Studentship)

Description: Titanium alloys are used widespread in aero jet engines as disk and fan blade material. In flight the components experience tensile stresses due to the high rotation speed of the turbine. The stress reaches its maximum value during the climb of the plane and is reduced when it is cruising. In terms of fatigue, one flight consists of periods with constant high stresses (dwell) and cyclic loadings at lower stresses. Traditionally fatigue experiments are carried out at either pure dwell or cyclic loading condition but are rarely combined. It is little known about the interaction of different fatigue regimes, which are present in real service. The objective is to characterize the initiation and propagation of fatigue cracks under consideration of the microstructure, microtexture and combined loading conditions. The spectrum of employed methods ranges from fractography, EBSD analysis to TEM.

Victor Wan - Fundamental modelling studies of crack nucleation and microstructurally short crack growth in superalloys

Investigator: Victor Wan

Supervisor: Professor Fionn Dunne

Collaborators: Dr Duncan Maclachlan / Rolls Royce Lifing and Methods Group

Duration: 01/10/2013 - 31/03/2016

Description:This PhD research is to address modelling techniques at the single crystal length scale within polycrystalline nickel alloys for fatigue crack nucleation and growth up to the crack length at which continuum assumptions become reasonable. Initial work is to address crack nucleation fatigue indicator parameters (FIPs) at the grain level but within polycrystal aggregates, through to the development of micro-cracking within a single grain. The full anisotropic nature of both elasticity and slip at the crystallographic level are to be addressed in the context of fracture toughness measures. The work is to further consider crack growth but within a single grain, taking full account of the anisotropy, and to address the appropriate computational tools within a crystal plasticity finite element context. Concerns of crack transfer across a grain boundary and subsequent growth through multiple grains will also be taken into account up to the circumstances at which conventional growth laws become applicable.

Hannah Weekes - Micromechanics of hydrides in zirconium alloys

Investigator: Hannah Weekes

Supervisors: Dr David Dye and Professor Trevor Lindley

Collaborators: Dr. David Rugg (Rolls-Royce)

Duration: 3/10/2011 - 3/10/2014 (PhD Studentship - Rolls-Royce/EPSRC)

Description: Zirconium alloys are continually being used throughout the nuclear industry due to their high performance under severe pressure and temperature conditions, coupled with their low thermal neutron absorption cross-section and high corrosion resistance in aqueous environments. However, high levels of hydrogen absorption during service have been found to result in the generation of detrimental hydride precipitation weakening the alloy integrity - a key issue when considering reactor storage post-service. This project incorporates extensive in-situ synchrotron work, including micro-beam Laue indentation on hydride containing micropillars in order to further our understanding of deformation characteristics, as well as x-ray diffraction experiments regarding a) high pressure deformation of hydrided zirconium alloys and b) hydride reorientation due to the application of a tensile stress. Coupled with ex-situ low cycle fatigue testing, this matrix of work aims to further our understanding of the micro-mechanical behaviour of hydride containing zirconium alloys.

Tiantian Zhang - Understanding fatigue crack nucleation from inclusions in a powder nickel alloy using micromechanics

Investigator: Tiantian Zhang

Supervisors: Dr Barbara Shollock and Professor Fionn Dunne

Collaborators: Dr Mark Hardy, Rolls-Royce plc

Duration: 10/01/2012 - 12/31/2015 (PhD Studentship)

Description: The aim of the project is to develop a crystal plasticity model that describes the nucleation of fatigue cracks in a powder metallurgy nickel base superalloy (RR1000). The nature of the inclusions and their local effect on the matrix (to include grain size and orientation and local strain) will be determined experimentally using electron microscopy. In addition, the inclusion/matrix interface will be studied. These experiments will be used to develop and validate finite element modelling approaches.

Dr Xinfang Zhang - A novel clean steel green processing method

Investigator: Dr Xinfang Zhang

Supervisors: Dr Rongshan Qin

Duration: 14/10/2012 - 13/10/2015 (PDRA)

Description:The project aims to develop a novel clean steel green processing method for the production of super clean steel with significantly reduced energy cost. The microstructure are observed by optical microscope, SEM, TEM, and XRD. The theory of thermodynamics and kinetics are considered to design the clean steel green process. The mechanical properties are performed to confirm the cleanliness of the steel.

Read more:

Zhang XF, Lu WJ, Qin RS, Removal of MnS inclusions in molten steel using electropulsing. Scripta Materialia, 2013, Vol. 69, Pages: 453-456.