Microstructure evolution and mechanical properties of as-cast and ultrasonic treated Nb-16Si-xCr alloys

Abstract

To improve the effect of solid solution strengthening of Nb-Si based alloys, the influence of Cr addition on microstructure evolution and mechanical properties, such as the compressive strength and the room-temperature fracture toughness of Nb-16Si-xCr alloys are studied by using vacuum non-consumable melting combined with ultrasonic vibration. Results show that with the Cr content increase, the silicide becomes more continuous, which causes easy crack propagation. The NbCr2 Laves phase is precipitated in Cr-rich region by addition of 4 at.% Cr. The element Cr is mainly dissolved in the Nb solid solution (Nbss) phase, the fracture toughness and compressive strength increase with the increasing of Cr content, which is attributed to the solid solution strengthening by Cr addition. However, the precipitated NbCr2 phase results in the significant decrease in mechanical performance. In order to eliminate NbCr2 phase and refine the coarse silicide, ultrasonic vibration is introduced into the Nb-Si-Cr melt. With the ultrasonic treatment for 60s, silicide has been refined and the NbCr2 phase disappear, the fracture toughness is 9.33 MPa m1/2 and the compressive strength is 2363 MPa, which are 39.5% and 14.8% higher than the as-cast Nb-16Si-6Cr alloy, respectively.