On the Influence of Microstructure on the Mechanical Behaviour of Ti-5Al-5Mo-5V-3Cr

High strength metastable beta titanium alloys, e.g. Ti-5Al-5Mo-5V-3Cr (Ti-5-5-5-3), are currently used in large components such as the truck beam in landing gear assemblies.  Unlike other classes of titanium alloys, metastable beta alloys can be processed to develop a wide range of microstructures, all of which can influence the mechanical properties of the final component, e.g. strength, fatigue and fracture toughness.  This ability to tailor the microstructure has resulted in significant interest into possible applications of these alloys into areas of the airframe traditionally dominated by other alloy classes. Thus, properties previously thought to be second order, such as high cycle fatigue (HCF) life have become important.

A recently developed heat treatment schedule has produced a lower strength yet more damage tolerant microstructure in Ti-5-5-5-3 and such material was reported to have a 1x10⁷ cyclic endurance stress ~ 50% greater than that of Ti-6Al-4V.  However, relatively little is known about the relationship between microstructure and micro-mechanisms governing the mechanical behaviour.  Here, results from a study investigating the role of two different microstructural conditions on the mechanical properties of Ti-5-5-5-3 will be presented, and used to identify key microstructure – property relationships.