Research On Microstructures Of Ti-6al-4me(me=mo,cr) Alloys

The optical microscopy, scanning electron microscopy, transmission electron microscopy have been used in order to reveal the effects of solution and aging treatments on the microstructure, deformation behaviors of the Ti-6Al-4Me (Me=Mo, Cr) alloys.It is observed that there are homogeneously distributed duplex matrix structure containing a andβphases in both Ti-6Al-4Mo and Ti-6Al-4Cr alloys after (α+β) solution treatment, while the structure is finer andβphase in Ti-6Al-4Mo alloy is less than those in the other one. However, mainly a phase and a small part ofβphase compose the typical Widmanstatten structure which dominates the microstructure of either of the alloy after (α+β) solution treatment and applied aging treatments. Besides, no precipitates could be detected in the Ti-6Al-4Mo alloy after all heat treatments process, while the Laves phase(a-TiCr2) is detected in the Ti-6Al-4Cr alloy if it is aging at low temperature(600℃) although it disappears at higher aging temperature(700℃,800℃). It was interesting to note that a solid solution of Cr existed in Ti-6Al-4Cr alloy under all conditions. The Cr solid solution appeared as lamina and is considered to form from a phase, which is controlled by the solubility and diffusivity of Cr elements in Ti solution.Ti-6Al-4Mo alloy has the same deformation configurations as Ti-6Al-4Cr for same given heat treatments. Great amount dislocations generate in the grain and some of them arrange in arrays after solution treatments, meantime twinning is also evident adjacent to grain boundary. In contrast, dislocations and twins could be found in a phase after aging treatment, and the twins could pass through the interphase from a phase toβphase. Furthermore, Ti-6Al-4Mo and Ti-6Al-4Cr alloys have also a very similar trend in hardness as function of heat treatment conditions in spite that Ti-6Al-4Mo alloy is harder than Ti-6Al-4Cr alloy at all applied conditions which was due to effective strengthening effect of Cr addition. The hardness gains increment due to aging after solution treatment but decreases if the aging temperature is raised.