Effects of alloying on the microstructures and mechanical property of Nb-Mo-Si based in situ composites

Nb-Mo-Si based alloys have been prepared by arc melting in a water-cooled copper crucible under an argon atmosphere. The effects of Al, Cr, Hf and Ti additions on the phase components and stability, microstructures and mechanical property of Nb-Mo-Si based alloys have been studied. The results indicated that the additions of Al, Cr and Ti elements do not change the phase components of Nb-20Si-6Mo alloys, which are composed of Nb solid solution (Nb-ss) and beta-Nb5Si3. The phase component is alpha-Nb5Si3 and Nb-ss in Nb-20Si-6Mo-3Hf alloy. The additions of Cr and Ti element make the Nb-ss/Nb5Si3 eutectic morphology anomalous and coarsening. The element segregation is obvious found with the additions of Hf and Ti. The enrichments of Hf and Ti change the compositions of retained melt and promote the formation of fine eutectic structure. After heating treatment at 1873K for 10 h, beta-Nb5Si3 phase translates into alpha-Nb5Si3 phase and gamma-Nb5Si3 phase. The eutectic structures tend to anomalous and coarsening. The Ti solid solution (Ti-ss) phase was found in Nb-20Si-6Mo-20Ti alloy and the formation mechanism of Ti-ss phase was discussed. The high temperature (1523 K) compression strength of as cast Nb-Mo-Si based alloys increased with the additions of Al, Cr, Hf, and decreased with Ti addition.