Characterization of spark-eroded shape memory alloy powders obtained in cryogenic liquids

Abstract

Fine powders of Ti–Ni–Zr–Cu and Ni–Mn–Ga alloys with the particle dimensions ranging from tenths of micrometers down to 10 nm have been prepared by the spark erosion method in liquid nitrogen and argon. The as-processed powder particles with typical sizes less than 50–70 μm have a spherical shape. There are some pores within some of the spherical particles. The surface of the spherical particles shows bubble-like features. The chemical compositions of the powders were practically similar to the compositions of the origin materials. The powders obtained in cryogenic liquids were almost free of the carbon contamination. Both austenitic and martensitic phases were found in Ti–Ni–Zr–Cu powders at room temperature. To activate martensitic transformations in smallest powder particles of Ni–Mn–Ga, preliminary thermal treatments of the as-sparked powders were required.