Microstructure and mechanical properties of the heat treated Nb-16Si-22Ti-2Hf-2Cr-2Al alloy prepared by vacuum induction melting

The master alloy ingot with the nominal composition of Nb-16Si-22Ti-2Hf-2Cr-2Al was prepared by vacuum non-consumable arc-melting and then vacuum induction melting. The melt was poured in a ceramic mould (Y₂O₃) with the temperature gradient of about 4 ℃/mm. The ingot with the dimension of Φ 60 mm×170 mm was fabricated. Heat treatment was conducted at 1500 ℃ for 100 h. The microstructure, room temperature tensile strength, as well as compression strength at 1250 ℃ of the heat treated ingot were described. Relationship between the microstructure and mechanical properties was also investigated. The results reveal that microstructure of the heat treated ingot is composed of Nb_SS dendrites, Nb₅Si₃ particles or lamellae and remaining Nb₃Si blocks. Room temperature tensile strength is in the range of 208 to 355 MPa. Both Nb₃Si and HfO₂ have detrimental effects on the tensile strength. The volume fraction of silicides is in proportion to the high temperature compression strength at 1250 ℃.