Microstructure and Properties of Microstructurally Refined Cast Ti46Al8Nb and Ti46Al8Ta

摘要

Cast samples of Ti46A18Nb and of Ti46A18Ta have been heat treated to produce a refined "convoluted" microstructure by Hot Isostatically Pressing (HIPping) massively transformed samples in the (alpha+gamma) phase field. The ductilities of these heat treated samples are increased from less than 0. 2% in HIPped cast samples to 0. 5% for the Nbcontaining alloy and to over 1% for the Ta-containing alloy. Detailed microstructural analysis has been carried out on samples failed in tension and on samples deformed in compression to understand the origin of the improved ductilities and also to understand the difference in the ductilities of the convoluted Nb-containing and Ta-containing alloys. Dislocation behaviour in regions of polycrystalline samples that are constrained to deform via slip transfer from gamma to alpha and by the glide of 1/3<11-26>dislocations have been compared in the two alloys with dislocation behaviour in regions where slip can occur mainly within each phase without involving slip transfer. The observations are discussed in terms of the build up of internal stress at alpha2/gamma interfaces which may lead to fracture at lower strains in the Nb-containing alloy.