Reducing Emissions by Exploiting Field-Induced Martensitic Transformations

Lead Research Organisation: Imperial College London
Department Name: Materials

Abstract

The aim of the the fellowship will be to develop the analysis tools to design and use materials that exploit stress- and electromagnetic field-affected phase transformations. This area extends from bainite and martensite in steels to the variant selection problem during the beta->alpha transformation in titanium and zirconium alloys, from omega superelasticity in the beta-Ti alloy GUM metal to NiTi shape memory alloys (SMAs) and ferromagnetic SMAs. In the component context, conventional SMAs rely on a temperature change to provide actuation, which is achieved either passively in response to the environment or by heating / cooling using bleed air, resistance heating or heating filaments. Ferromagnetic SMAs use an electromagnetic field, which allows much faster switching, for example in a pump or to improve flow control. While the crystallography of these transformations is well understood, models are not generally available for the micromechanics that can be incorporated into Finite Element (FE) descriptions of component behaviour used by designers. In addition, whilst these systems are clearly tractable to atomistic approaches, atomistic modeling is still too immature to reliably design new alloys without experimental support; however approaches such as density functional theory (DFT) can enable insight into alloy design approaches to be developed. A subsidiary aim will be to start to bridge the gap to the DFT community. In conventional alloys the problem is often complicated by a diffusional component to the transformation, or nucleation may be the limiting step. However, we have recently shown clearly that applied stress can bias variant selection, leading to the production of mono-variant transformed beta grains in Ti-6246, with consequent effects on properties. The ability to model variant selection in diffusionless transformations, such as in martensite in steels, omega in Ti and Zr, and in (f)SMAs will be a prerequisite to modeling the more complicated problem in Ti-64 and Ti-6246. Industrially, the major goal of the fellowship will be to build a capability to model such transformations and to design alloys exploiting them for use in aerospace, automotive and power applications, with QinetiQ, Rolls-Royce, Timet, Corus and DSTL.
 
Description Shear at the microscopic scale is often exploited, or a degradation mechanism in, the metallic materials that power our world.

In zirconium in nuclear reactors, brittle hydrides are precipitated during cooling - in this work we have shown for the first time using sub-micrometre X-ray beams, that these hydrides can plastically deform in a microstructure, which helps us start to unpick how they embrittle spent nuclear fuel can.

In shape memory alloys, we now understand how these materials degrade during repeated actuation, by accumulating defects at the interfaces of the shearing phase that provides the shape change. We also understand how to tailor that interface such that these defects do not accumulate, providing a roadmap for cyclically stable actuator alloy development, opening up real engineering uses for these materials.

In biomedical and superelastic titanium alloys, which excite much currency interest in the community, we were able to identify that these alloys are not thermally or mechanically stable, but can be used as damping materials - a sort of metallic rubber. Again, the interface plays a key role, as does aluminium, providing possibilities to develop these alloys further for stability and thence, large scale application.

In titanium alloys in jet engines, we were able to resolve a stress corrosion cracking problem - again, one involving hydrogen embrittlement, and retire over £50m/yr worth of cost to Rolls-Royce.
Exploitation Route The materials development activities have shown how superelastic and twinning alloys deform, contributing to the development of TWIP steels (current UK MOD / Tata / Timet program), to our understanding of superelastic and shape memory materials (e.g. Nature Materials invited comment), and to the scope of applicability of these materials (e.g. to jet engines with Rolls-Royce).
Sectors Aerospace, Defence and Marine,Healthcare,Manufacturing, including Industrial Biotechology,Security and Diplomacy,Transport

 
Description Rolls-Royce have evaluated the use of superelastic beta-Ti alloys for use in jet engines; we concluded that the existing alloys had some problems that prevent their adoption but that the underlying concept is sound. One of the PhDs in this programme resulted in some pathways to develop alloys that avoid these problems. Much of the work in this programme around oxygen levels has resulted in the development of a technique for measuring oxygen levels in titanium surfaces, which been critical to resolving some significant service issues, saving >£40m in 2015 alone. The TWIP steels work is currently resulting in scale-up work with Tata steel to develop a new automotive opportunity for them. The zirconium hydrides work has been useful to supporting Rolls-Royce submarines' understanding of how these materials behave in service.
First Year Of Impact 2014
Sector Aerospace, Defence and Marine
Impact Types Economic

 
Description EPSRC Programme Grant (Hexmat)
Amount £4,979,741 (GBP)
Funding ID EP/K034332/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 04/2013 
End 05/2018
 
Description EPSRC Programme grant (DARE)
Amount £3,226,486 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 08/2014 
End 09/2019
 
Description SPII
Amount £7,939,564 (GBP)
Funding ID EP/M005607/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 09/2014 
End 09/2019
 
Description Rolls-Royce plc 
Organisation Rolls Royce Group Plc
Country United Kingdom 
Sector Private 
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