Microstructural and mechanical characterization of a fine-grained and textured Ni51Ti49 alloy prepared by rapid solidification and processed by solution treatment

Microstructural characteristics and mechanical property of Ni₅₁Ti₄₉ alloys fabricated by means of rapid solidification technology followed by solution treatment were systematically investigated by using XRD, SEM, EBSD and micro-hardness test. The as-cast alloy strips show fine-grained microstructure with average grain size around 5 μm and a strong fiber texture (<001>_B2//ND). After undergoing solution treatment with various temperatures ranging from 800 ºC to 1050 ºC for 5 hours, the alloy strip samples still show the microstructural feature of fine grains and fiber texture, which are inherited perfectly from the as-cast alloys. Notably, average grain size increases slightly from 7.5 μm to 11.7 μm with increasing the solution treatment temperature from 800 ºC to 1050 ºC. Phenomenon of abnormal grain growth that easily causes multiple-stage martensitic transformation in NiTi alloys during aging can not be found in solution-treated samples. Moreover, the micro-hardness of the solution-treated alloys increases from 272 HV to 411 HV with increasing solution treatment temperature from 800 ºC to 1050 ºC. This indicates that the solution strengthening effect is more remarkable with a higher solution temperature due to the increase of quenched-in defect concentration.