Effect of Particle Size of Titanium and Nickel on the Synthesis of NiTi by TE-SHS

In this work, the influence of the particle size of nickel and titanium on the synthesis of NiTi shape memory alloy by self-propagating high-temperature synthesis (SHS) was investigated. It was found that coarse titanium and nickel powders undergo only a limited SHS reaction. On the other hand, too fine powders support the low-temperature diffusional formation of NiTi intermetallics at 773 K to 1073 K (500 °C to 800 °C) which could then suppress the SHS reaction. The optimum powder fraction of both nickel and titanium to achieve the most intensive SHS reaction is 25 to 45 µ m. The influence of the particle size of both nickel and titanium on the reaction mechanism is discussed in terms of the microstructure evolution, phase, and chemical composition changes and thermal effects determined by differential thermal analysis.