Fabrication Of TiAl Based Alloy By Powder Metallurgy And Study On Property

TiAl based alloys are widely studied because their light weight and excellent elevated temperature properties such as high strength retention, resistance to creep and oxidation. However, their application is currently limited by the poor ductility and strong resistance to deformation at elevated temperature. In addition, it is difficult to prepare TiAl alloy with fine and homogeneous microstructure by traditional casting and mechanical working processes. Therefore, a new technology, which consists of the mechanical blending, reactive sintering and hot hydrostatic extrusion, has been put forward.The material of the experiment is the mixture of Ti and Al elemental powders prepared by mechanical blending for 72 hours and than consolidating into densified billets. The powder billets need reactive sintering at low temperature and high temperature, in order to get high densified TiAl alloy. And then hot hydrostatic extrusion is used to press the sintered billets. By high-temperature compression test of the obtained samples, the mechanical properties of TiAl based alloy were investigated. The following aspects have been researched on.Low temperature reactive sintering was studied. The expansion during the vacuum reactive sintering at low temperature of the powder billets was experimentally investigated, and the reasons of expansion were theoretically analyzed. The method of low temperature reactive sintering was generalized, and the experiment testified the method effective.The following aspects were accomplished after high temperature reactive sintering. The rule of the shrinkage of the billets was generalized from the result of density of the billets, which have been reactive sintering at high temperature. By X-Ray analysis of the obtained samples the degree of the reaction was researched when the temperature and time changed. At last the regularity of the metallurgical structure of TiAl alloy was investigated, when the high temperature and time changed.The following aspects were accomplished after hot hydrostatic extrusion. The density of the billets got bigger after hot hydrostatic extrusion. By high- temperature compression test of the obtained samples, the mechanical properties of TiAl based alloy were investigated. The influence of testing temperature on the compressive yield strength of as-sintered alloy has been made clear.