High-temperature strength and room-temperature toughness of Nb-W-Si-B alloys prepared by arc-melting

As next generation ultra-high temperature structural materials, the balance between high-temperature strength and room-temperature toughness of the Nb-base in-situ composites is the most important issue. This paper investigated the mechanical behavior of Nb-10W-10Si-xB (x = 0, 0. 1, 1 and 2). Materials were prepared by arc-melting and annealed at 1870 K for 100 h. The microstructures of the Nb-10W-10Si-xB But those were increased at 2 mol% B. All the alloys have more than 7% compressive ductility at room temperature. B improves both the room-temperature toughness (K-Q) and the high-temperature strength (sigma(max)). The K-Q and the sigma(max) of the Nb-10W- 10Si alloy at 1670 K are 8.2 MPa m(1/2) and 400 MPa, respectively, and are 8.8 MPa m(1/2) and 470 MPa in the Nb-10W-10Si-2B alloy. With two-phase Nb-ss/Nb5Si3 microstructures, the compressive damage at high temperature was dominated by debonding of the interfaces between the primary Nb-ss and the 5-3 silicide, while the fracture mode at room temperature is transgranular, controlled by the primary Nbss cleavage. (C) 2003 Elsevier B.V. All rights reserved.