Thermomechanical Behaviour of Multi-Functional Titanium Alloys
28 August 2007
A team of Japanese researchers (Saito et al., Science, vol. 300, p.464, 2003) have recently discovered a new class of titanium alloy (termed Gum Metal®) exhibiting a remarkable combination of properties: low elastic modulus, ultra-high strength, large elasticity, little or no work hardening at ambient temperature and Invar & Elinvar properties over a wide temperature range. These Ti-24at.%(Ta+Nb+V)-(Zr,Hf)-O alloys exhibit this unusual combination of properties only after cold deformation and is argued to be associated both with the electronic configuration of the alloy and deformation occurring via a dislocation-free mechanism.
Figure 1: Mechanical properties of Gum Metal® showing the considerable expansion of property space, adapted from Saito et al., Science, vol. 300, p.464, 2003.
Taking key properties such as elastic modulus and strength, Figure 1 shows how these types of alloy push the current limits of property space where no materials are currently available. For example, it is often desirable to produce materials exhibiting a low elastic modulus and high strength as they are not only flexible but the high yield strength ensures their resistance to plastic deformation. These properties allows the material to be used in a range of technological applications such as springs, metal seals, medical equipment, sporting equipment and artificial bones or implants; the latter application being extremely interesting due to the desirable mechanical behaviour and compatibility of beta titanium alloys with the human body.
A project is in progress in the UNSW node of the ARC Centre of Excellence for Design in Light Metals aimed at understanding the microstructure and properties of a these titanium alloys fabricated by powder metallurgy and a new thermomechanical processing route. The work is being carried out by Prof. Michael Ferry and Gregory Guo who is currently working on a PhD on the development of microstructure and texture during cold deformation and subsequent annealing and is clarifying the role of dislocations on the mechanical behaviour of these alloys. This work is expected to provide a platform for a more detailed study of the stability of the alloy against impact damage and fatigue in situations involving complex cycles of loading. Further work will involve an assessment of various important mechanical properties and the feasibility of net-shape fabrication processing to produce large-sized components.
Professor Michael Ferry
ARC Centre of Excellence for Design in Light Metals