Powder metallurgical production of TiNiNb and TiNiCu shape memory alloys by combination of pre-alloyed and elemental powders

摘要

The common Ti_(44)Ni_(47)Nb_9 and Ti_(50)Ni_(40)Cu_(10) ternary shape memory alloys were produced by sintering techniques and the microstructure, phase structure and phase transformation behaviour were investigated. A combination of pre-alloyed binary TiNi powder and elemental Nb,.Ni and Cu, Ti powders, respectively, were used. In contrast to the use of pre-alloyed ternary powders, which have to be produced in each new composition, a higher flexibility in the alloy composition becomes possible. In case of the Ti_(44)Ni_(47)Nb_9alloy, liquid phase sintering was done to obtain the eutectic phase structure known from cast material. In case of the Ti_(50)Ni_(40)Cu_(10) alloy, the pore size and porosity can be improved by choosing a two-step sintering process, as a eutectic melt between Ti and Cu is formed at low temperatures which influences the sintering behaviour. Controlling the impurity contents and the resulting secondary phases is necessary for both alloys in the same way as for binary TiNi alloys.