Effect of Re addition on microstructure and mechanical properties of Nb-Si-Ti-Al-Cr-Hf ultrahigh temperature alloys

In order to improve the mechanical performance of multicomponent Nb-Si based alloy, the effects of rare metal element Re addition on microstructure evolution and mechanical performance of Nb-16Si-20Ti-2Al-2Cr-2Hf (at. % as follows) alloys are studied systematically. With the high melting point alloying element Re addition, the primary Nbss phase of Nb-16Si-20Ti-2Al-2Cr-2Hf-xRe transforms from equiaxed structure to dendritic structure due to the component supercooling, and the silicide phase transforms from alpha-Nb5Si3 to beta-Nb5Si3. Moreover, with the increasing Re addition, the microstructure has been refined firstly, then coarsened and finally formed developed dendrite. The element Re preferentially solubilizes in the Nbss phase, when the Re content exceeds 1.0%, it can be detected in silicide phase. The Vickers microhardness and compressive strength of the multi component Nb-Si based alloys have been improved significantly because of the solid solution strengthening by Re addition. And the most obvious improvement is the room temperature fracture toughness increases from 10.33 MPa m(1/2) to 14.40 MPa m(1/2), as the Re content increases from 0 at.% to 0.5 at.%, which is 39.4% higher than the Re free Nb-Si based alloy.