In order to maintain the rate at which the aerospace industry has grown in recent years, new aircraft are being designed with high emphasis on increased payloads. With this increase in payload, improvements in engine thrust output and efficiency are required. It is well known that one method of improving efficiency is to operate engines at high temperatures resulting in engine manufacturers increasingly choosing nickel based super alloys in favour of titanium alloys.
In order to successfully displace nickel with titanium in high temperature gas turbine conditions, a new titanium alloy is required to operate at temperatures exceeding the capabilities of existing alloy systems. While temperature is of utmost importance to this application, a number of other properties are to be considered during design. Materials must exhibit good creep and fatigue resistance as well as high strength and excellent corrosion resistance. Similarly, reasonable room temperature ductility must be employed to facilitate component manufacture.
The results prove the benefits of the addition of silicon to titanium alloys, however the loss in room temperature ductility brought by the addition of silicon to α-titanium has led to concentration on the use of β stabilisers to alloys of the Ti-Si system. An industry driven suggestion basing alloy design on analogies from nickel based super alloys, appears to have potential to provide improved ductility to such alloying system.
Through a combination of precipitation hardening and the formation of a protective oxide scale, titanium alloys containing chromium, niobium and silicon have proven to exhibit comparable and better oxidation resistance to Timetal 834 as well as improved tensile strength. Although ductility has still been outlined as a potential issue for such alloys, it would be beneficial to investigate the effect of the material processing route, and therefore the starting microstructure of such alloys.
