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

The Nbss/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 Nbss 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.