Characterization Studies of Ni50Ti50-xZrx Shape Memory Alloys Produced by Spark Plasma Sintering

In the last few years high temperature shape memory alloys (HTSMAs) have gained attention as a thrust area of research. NiTiZr alloys, though economically most viable, tend to be brittle and are difficult to process when produced by the conventional casting route. The current work adopts powder metallurgy with a view to producing fine-grained alloys as well as avoiding secondary processing. Nickel, titanium and zirconium powders were wet-milled in a high energy planetary ball mill using tungsten carbide balls and vials. The as-milled powders were then spark plasma sintered at temperatures of 800 ºC and 900 ºC. The as-sintered samples were subsequently homogenized at temperatures between 900 ºC and 1050 ºC. X-ray diffraction analysis was carried out to confirm mechanical alloying in the milled powders and to analyze the phase evolution in the sintered samples as a function of the homogenization treatment. The microstructures of the as-sintered and heat treated samples were characterized by SEM and EDX, while their transformation temperatures were determined by differential scanning calorimetry. Nanoindentation studies were carried out to determine the Young’s modulus and to correlate load-displacement curves to the shape memory properties.