Effects of high temperature heat treatment on the microstructure of Nb-Cr based multi-element alloy

A master alloy ingot of Nb-Cr based multi-element alloy has been prepared by a vacuum non-consumable arc-melting and then a vacuum consumable arc-melting. The samples are then heat treated at 1250°C/24 h, 1350°C/24 h and 1450°C/24 h, respectively. Both the arc-melted microstructure and the heat-treated microstructure are characterized by using X-ray diffractometer, optical microscope (OM) and scanning electron microscope (SEM) equipped with energy dispersive spectrum analyzer (EDS). The results show that the arc-melted microstructure was composed of Nb solid solution (Nbss) dendrites and Laves Cr₂(Nb, Ti, Hf) blocks dispersed in the Nbss dendrite intervals; after heat treatments, the phase constituents of alloy are same as those in the arc-melted microstructure. However, the microstructure is refined, and the Nbss dendrites disappear and are transformed into equiaxed crystals. Furthermore, the fine and dispersed secondary Cr₂(Nb, Ti, Hf) are precipitated in the Nbss matrix. With the increase of heat treatment temperature, the microstructure became finer, and the amount of Cr₂(Nb, Ti, Hf) increases.