Effect of (Si+Al) Content in Nb Solid Solution on Mechanical Properties of Multiphase Nb-Si-Al Alloys

In this study we have investigated the effect of mechanical properties of Nb solid solution (Nbss) on toughness and strength of multiphase alloys in Nb-Si-Al ternary systems. Especially, we focused on the effect of (Si+Al) content in Nbss as the constituent of the multiphase alloys. Nbss is equilibrated with Nb3Al and/or Nb5Si3 in Nb-Si-Al ternary phase diagram. Nbss in equilibrium with Nbss+Nb3Al+Nb5Si3 three-phases in the Nb-Si-Al ternary system has significantly lower solute content compared with Nbss in equilibrium with Nb3Al in Nb-Al binary system. Based on the obtained results of Nb-Si-Al phase diagram, we prepared the samples of Nbss single-phase alloys, Nbss+Nb3Al, Nbss+Nb5Si3 and Nbss+Nb3Al+Nb5Si3 multiphase alloys and investigated the toughness and the strength. The toughness was estimated by Small Punch (SP) tests and the strength was estimated by tensile tests at room temperature and compression tests at high temperature. The toughness of Nbss single-phase alloys and multiphase alloys estimated from SP energy increases with decreasing (Si+Al) content in Nbss. Nbss+Nb3Al+Nb5Si3 multiphase alloys are found to be promising because of not only high toughness (KIC) value estimated from SP tests but also high strength at elevated temperature.