Synthesis of novel structured NiTi

long range diffusion of Ti and Ni through the stable Ti2Ni and TiNi3 phase regions. It was found that elemental powder sintering did not result in single phase TiNi, consistent with the expectation of the diffusion model. Instead, multi-phases including Ti2Ni, TiNi and TiNi3 were found to co-exist in the microstructure after heating to high temperatures for long durations. This implies similar thermodynamic stabilities of the three phases. At the meantime, the co-existence of the three phases does not conform to equilibrium thermodynamic principles, implying that the phase formation had not ii occurred in one thermodynamically equilibrium process during sintering, instead in two spatially separate processes, as predicted by the model (stated above). SEM/EDS analysis revealed the formation of the two types of TiNi, approximately Ti-49.5at%Ni corresponding to TiNi(I) from the Ti side and Ti-51at%Ni corresponding to TiNi(II) from the Ni side, confirming the prediction of the model. The use of pore forming agents did not alter the rule of solid state phase formation, and their effect was limited to pore structure morphology. The sintered specimens exhibited low transformation heat and wide transformation intervals, and poor shape memory behaviour and mechanical properties. This is obviously related the presence of large amounts of Ti2Ni and TiNi3 intermetallic compounds...