Synchronous improvement in room-temperature fracture toughness and high-temperature oxidation resistance of Nb[sbnd]Si based alloys with Erbium addition

Abstract

The microstructure, room-temperature fracture toughness and high-temperature oxidation resistance of Nb-16Si-23Ti-4Cr-2Al-2Hf-xEr (x = 0, 0.1, 0.4, 0.6, at.%) alloys via directional solidification and heat treatment were investigated. Results showed that all the alloys consisted of Nbss, αNb5Si3 and γNb5Si3 phase, Er addition refined the microstructure, increased the volume fraction and continuity of Nbss matrix. Since the high-activity of Erbium, it is in-situ oxygenated to form a mixed oxide phase in the form of discreet particles, alloy melt got purification by internal oxidation mechanism. The higher density dislocations which may be induced by thermal expansion mismatch were piled up around the oxide particle compared with other regions in Nbss matrix. Er-doping contributed to eliminate segregation of Ti and then reduced its concentration-sensitive effect. Besides, more Nbss/silicide interface decohesion was triggered by addition of Er. So the 0.4 at.% Er addition significantly enhanced the fracture toughness of NbSi based alloys from 8.4 MPa·m1/2 to 24.5 MPa·m1/2 at room temperature. Er also accelerated the formation of complex oxide products and transition from linear oxidized regularity to parabolic, and obviously decreased the weight gain from 258.2 mg/cm2 to 164.3 mg/cm2 after oxidation at 1300 °C for 100 h.