Structure and Properties of Ti_(28)Ni_(50)Hf_(22) Powder Alloy

摘要

The effect of consolidation and thermal treatment on the structure, local chemical composition, and martensite transformation temperatures of the Ti_(28)Ni_(50)Hf_(22) powder alloy is studied. It is shown that, in the powder state, the alloy is characterized by an inhomogeneous distribution of Ti and Hf in the matrix, whose concentration spread may reach 27 at %. Vacuum sintering and homogenizing annealing lead to equalization of the chemical composition. During powder sintering, the spread of Ti and Hf concentrations reduces from 27 to 2 at %. Subsequent vacuum annealing at a temperature of 1000°C for 4 h for a sintered sample additionally reduces the spread of concentrations from 4 to 2 at %, while the increase in the annealing duration from 4 to 16 h does not affect the uniformity of the element distribution. It is established that, at a large inhomogeneity of the chemical composition, the differential scanning calorimetry (DSC) methods fail to record the occurrence of martensitic transformation in the melt. However, homogenization of the alloy leads to the appearance of endothermic peaks on the DSC curve upon heating, as well as to narrowing of the interval of reverse martensitic transformation.