Abstract:The dependences of the microstructure and hardness of the binary Cr-Ta alloys ［Cr-9.0, -9.2, -9.4, -9.6, -9.8, and -13.0 Ta］ ( mole fraction, %) were investigated. When Ta content of the alloy is less than 9.4%,  there are primary dendrite grains of a Cr solid-solution phase existing in the matrix of Cr-Cr₂Ta eutectic colonies in the alloy. Moreover, the regular polygon grains of the primary Cr₂Ta Laves-phase are surrounded by the Cr-Cr₂Ta eutectic colony in the hyper-eutectic Cr-9.4%Ta alloys. The scanning electron microphotograph shows that one of the Cr₂Ta phase plates of an eutectic colony always connects with the primary Cr₂Ta Laves-phase grain in a hyper-eutectic alloy. The eutectic colony size of Cr-Ta alloys decreases with increasing Ta. In addition, the macrohardness of Cr-Ta alloys is influenced by the chemical composition at room temperature. The binary eutectic Cr-Ta alloy presents the lowest hardness on a macrohardness scale.

Key words: binary Cr-Ta alloys; Ta content; Laves-phase