An as-cast Nb-Si-based alloy with fine-grains and remarkable fracture toughness by minor Sc addition

Abstract

The effect of Sc addition on the phase composition, microstructure, and room-temperature fracture properties of arc melted Nb-Si-Ti-ZrC-based alloys was systematically investigated. The constituent phases of all alloys are Nbss, γ-(Nb,X)5Si3 and TiC. Sc refines the microstructure, while the grain sizes for the primary γ-(Nb,X)5Si3 and Nbss phases drop from 213 µm and 22.3–23 µm and 5.7 µm, respectively. The content of Nbss and TiC decreases with increasing Sc. The Sc dissolves and then softens Nbss phase. The degree of restraint of Nbss phase decreases with increasing Sc content, therefore causing formation of dimples in the fracture and interface decohesion. Because of the refinement of the primary γ-Nb5Si3 phase, the dimples and interface decohesion created by the low degree of constraint of Nbss phase, the KQ value of Sc3 alloy becomes 16.4 MPa·m1/2. The average grain size of Nbss phase becomes the lowest (5.7 µm), when 0.5 at% Sc is added. The small grain size of Nbss phase deteriorates room-temperature fracture toughness.