Microstructures and mechanical properties of Nb_ss/Nb₅Si₃ in-situ composite prepared by electromagnetic cold crucible directional solidification

The Nb_ss/Nb₅Si₃ in-situ composite with the nominal composition of Nb-24Ti-12Si-4Cr-4Al-2Hf (at%) has been successfully fabricated by electromagnetic cold crucible directional solidification. Microstructures of the initial transition (IT) zone and the steady-state growth (SSG) region were observed by scanning electron microscope, and their phase compositions were analyzed with X-ray diffraction (XRD). The room temperature fracture toughness and the tensile strength at 1250°C were measured. The results indicated that from IT zone to SSG zone, the major silicide transferred from γ-(Nb,Ti)₅Si₃ to β-(Nb,Ti)₅Si₃. The directional solidification microstructure with coupled Nb_ss and Nb₅Si₃ was created in SSG region. Compared SSG region with IT zone, the room temperature fracture toughness and the high temperature tensile strength increased about 50% and 24%, respectively, which was contributed to the directional solidification microstructure and the type transformation of silicide.