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

Abstract

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 alloys were primary Nb solid solution (Nb SS) and a eutectic of Nb SS/Nb 5Si 3 (5–3 silicide). At 0.1 and 1 mol% B contents, Vickers hardness and strength at room temperature were decreased. 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 ( σ max). The K Q and the σ 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/Nb 5Si 3 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 Nb SS cleavage.