Spark plasma sintering of TiNi nonopowders

Nano-size TiNi powder prepared by electro explosion of TiNi wire process was processed by spark plasma sintering for 5 minutes at variable temperatures between 700 and 1000°C. The shape memory effect and crystallography of both the powder and the sintered TiNi specimens were extensively characterized. The specimen sintered at a temperature of 700°C showed high porosity and partial densification, but with apparent shape memory effect. By contrast, the specimens sintered at higher sintering temperatures above 900°C showed high density, but experienced extensive oxidation with the resulting loss of the shape memory effect. High temperature sintering resulted in significant solid-state inter-diffusion of atoms and thus the formation of different intermetallic phases, such as NiTi ₂ and Ni ₃Ti. The phase transformation temperatures and enthalpies for the samples sintered at 700 and 800°C increased with increasing temperature. In addition, the differences between the start and finish transformation temperatures for the sintered specimens appear to be significantly narrower compared to those of the nano-powder.