Effective Structural Unit Size in Polycrystals: Formation, Quantification and Micromechanical Behaviour
Lead Research Organisation:
Swansea University
Department Name: College of Engineering
Abstract
The concept of grain size playing an important role in the engineering application of polycrystalline metals is well established. During casting and subsequent wrought processing, tried and tested methods are used to refine grain size in order to enhance ductility and increase tensile, yield and fatigue strengths. The advent of electron microscopy based experimental techniques such as electron back scatter diffraction (EBSD) and focussed ion beam (FIB) plus nano-indentation have provided novel, intriguing insights into the deeper aspects of both structural evolution and structure / property relationships. This has included preliminary identification of the critical role of effective structural unit size (rather than grain size) in determining mechanical behaviour. However, understanding of the the relationship between processing and effective structural unit size remains in its infancy for most systems. Consequently, significant progress can now be made in understanding the evolution of structures including recrystallisation processes and variant selection during phase transformation. This offers the potential of refining the structure of a wide range of engineering materials for which phase transformation plays an important role during processing such as steel, titanium, zirconium etc. The fatigue process is very complex but can be simplified conceptually into initiation and crack growth. For high cycle fatigue (HCF) regimes where the number of applied stress cycles can easily exceed 10,000,000 material evaluation relies on specimen or component testing. The majority of the HCF life is spent initiating a defect that then grows rapidly to failure. For materials subject to such HCF regimes, the design principle is to stay below an empirically defined endurance stress so that initiation is prevented. For low cycle fatigue (LCF) the situation is different in that initiation life and growth life can both be used to predict a safe component life. Typically, initiation is again determined empirically by mechanical testing. The current inability to predict fatigue initiation from basic principles stems from the fact that crack initiation is dominated by interactions from grain to grain which are inherently difficult to quantify and to model. Thus, for significant end user applications, the engineer has minimal knowledge defining what aspects of a material, or its processing, influence its performance other than by mechanical testing, which is very time consuming and expensive.Considerable scientific exploration of fatigue has until recently largely failed to assist the material producer and end user in other important ways. In the specific case of the titanium-based alloys, the definition of grain boundaries and subsequent measurement of grain size are notoriously difficult through optical inspection alone. The existence of large colonies of similarly orientated crystallographic units can encourage extensive planar slip structures to develop. In turn, through a process of stress redistribution between relatively weak and strong units , this can have a potentially disastrous effect on component performance. Key issues which determine mechanical properties of interest to the end user include:a) How boundaries behave and what constitutes a boundary for a given load regime.b) Factors in processing and heat treatment that dictate effective structural unit size.c) Modelling capability to provide quantitative predictions of mechanical behaviour including HCF initiation and short crack growth rates.All of these issues form the basis of the current proposal for research.
People |
ORCID iD |
Martin Bache (Principal Investigator) |
Publications
Martin R. Bache
(2011)
Crystal Plasticity and Quasi-Cleavage Facet Formation During Fatigue Loading
Martin R. Bache
(2011)
Crystal Plasticity and Quasi-Cleavage Facet Formation During Fatigue Loading
SACKETT E
(2007)
Crystal plasticity, fatigue crack initiation and fatigue performance of advanced titanium alloys
in International Journal of Fatigue
Bache M
(2009)
Experimental and crystal plasticity studies of deformation and crack nucleation in a titanium alloy
in The Journal of Strain Analysis for Engineering Design
Cameron Pleydell-Pearce
(2011)
Fatigue life variations due to microstructure in Ti 6Al 4V
Bache
(2019)
Microstructural Control of Fatigue Behaviour in a Novel ????? Titanium Alloy
in Metals
Description | The fatigue performance of alpha/beta and near alpha titanium alloys is intimately controlled by microstructural form and micro-texture. The current research enabled detailed understanding of such microstructure/property relationships in different variants of rolled and forged product produced by Timet UK for application by Rolls-Royce. |
Exploitation Route | Timet UK have been able to reverse engineer the knowledge gained during this project to optimise their standard rolling and forging processes, in particular with regards to avoiding extensive macrozone formation. Rolls-Royce have utilised the mechanical data and adopted this through their design database for the design and lifing of titanium components. |
Sectors | Aerospace, Defence and Marine,Energy,Manufacturing, including Industrial Biotechology,Transport |
Description | Timet UK have been able to reverse engineer the knowledge gained during this project to optimise their standard rolling and forging processes, in particular with regards to avoiding extensive macrozone formation. Rolls-Royce have utilised the mechanical data and adopted this through their design database for the design and lifing of titanium components. |
First Year Of Impact | 2009 |
Sector | Aerospace, Defence and Marine,Manufacturing, including Industrial Biotechology |
Impact Types | Economic |
Description | EPSRC Strategic Partnership EngD project support (J Hewitt) |
Amount | £40,000 (GBP) |
Funding ID | EPSRC Strategic Partnership in Structural Metals for Gas Turbine Applications (EngD - J. Hewitt) |
Organisation | Timet UK Ltd |
Sector | Private |
Country | United Kingdom |
Start | 09/2010 |
End | 09/2014 |
Description | KTN CASE award (P Davies) |
Amount | £90,000 (GBP) |
Funding ID | Materials KTN CASE #10001030 (PhD - P. Davies) |
Organisation | Timet UK Ltd |
Sector | Private |
Country | United Kingdom |
Start | 09/2010 |
End | 10/2013 |
Description | Timet UK: EPSRC Strategic Partnership in Structural Metals for Gas Turbine Applications (EngD Project support - W. Davey) |
Amount | £40,000 (GBP) |
Organisation | Timet UK Ltd |
Sector | Private |
Country | United Kingdom |
Start | 01/2016 |
End | 12/2020 |
Description | Titanium alloys - RR Technology Transfer |
Organisation | Rolls Royce Group Plc |
Country | United Kingdom |
Sector | Private |
PI Contribution | Swansea University provided key mechanical property investigations and fatigue characterisation of a range of textured titanium alloy products in order to improve the understanding of controlling micro-texture / microstructure relationships. |
Collaborator Contribution | Technical expertise was provided towards this research by a range of staff employed by Rolls-Royce plc. Together with fellow academic investigators from the partner Universities, company representatives attended regular technical and management review meetings. |
Impact | Collaboration between Rolls-Royce plc and Swansea UTC into titanium based technologies continues under a range of ongoing postgraduate and postdoctoral research projects. Prof Martin Bache (Swansea UTC Director) is a regular contributor to company non advocate reviews (NARs) aligned to titanium based components and associated service. |
Description | Titanium alloys - Timet UK Technology Transfer |
Organisation | Timet UK Ltd |
Country | United Kingdom |
Sector | Private |
PI Contribution | Swansea University provided key mechanical property investigations and fatigue characterisation of a range of textured titanium alloy products in order to improve the understanding of controlling micro-texture / microstructure relationships. |
Collaborator Contribution | Technical expertise was provided towards this research by a range of staff employed by Timet UK. Together with fellow academic investigators from the partner Universities, company representatives attended regular technical and management review meetings. |
Impact | Collaboration between Timet UK and Swansea University into titanium based technologies continues under a range of ongoing postgraduate and postdoctoral research projects. Over the past five years this has included projects to develop novel fan disc and containment alloys and attempts to extend the temperature capabilities of existing alloys for intercases. |
Description | Fatigue Damage in Structural Materials (Conference series, Hyannis, USA) |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | International conference held every two years in Hyannis, Massachussetts, USA focussed on fatigue behaviour in advanced structural metals. Draws an audience approaching 200 delegates from academia, industry and defence sectors. Prof Bache has acted as an invited member of the International Scientific Committee for 18 years and held the position of Conference Chairman for three events. This series of meetings is renowned for the vigorous technical debates amongst the International fatigue community, encouraged by the single session format. Papers submitted to this conference are published in the International Journal of Fatigue (impact factor ~ 2) subject to standard review criteria. |
Year(s) Of Engagement Activity | Pre-2006,2006,2008,2010,2012,2014 |
URL | http://www.fatiguedamageconference.com/ |