Understanding the behaviour of Ti-5Al-5Mo-5V-3Cr during subtransus isothermal forging

Ti-5Al-5Mo-5V-3Cr(Ti-5-5-5-3)has become the alloy of choice for large scale high strength forgings in the aerospace industry, for example the truck beam in landing gear assemblies. The current processing route for these components requires multiple hot forging steps, which influence the in service properties of the material. Recently, significant effort has been made to characterise and understand the behaviour of Ti-5-5-5-3 during isothermal forging to enable the through process prediction of both microstructural evolution and mechanical properties. This paper evaluates the flow behaviour in relation to process temperature, strain rate, initial microstructural condition and the influence of lubrication. Macroscopic grain flow and strain distribution within the workpiece were influenced by the friction factor generated by the application of different lubricants, however the shape and magnitude of the mean flow stress appeared to be unaffected. Temperature and strain rate alter the magnitude of mean flow stress, whilst the shape of the curve was found to be directly related to the high temperature microstructure. The morphology and size of the alpha phase precipitates were found to have a substantial influence on the peak strength and the extent of flow softening, whilst steady state flow was dominated by dynamic recovery of the beta phase. These observations are found to be consistent with other high strength meta-stable beta alloys such as Ti-10V-2Fe-3Al.