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 alloys were primary Nb solid solution (NbSS) and a eutectic of NbSS/Nb5Si3 (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 (KQ) and the high-temperature strength (σmax). The KQ and the σmax of the Nb–10W–10Si alloy at 1670 K are 8.2 MPa m1/2 and 400 MPa, respectively, and are 8.8 MPa m1/2 and 470 MPa in the Nb–10W–10Si–2B alloy. With two-phase NbSS/Nb5Si3 microstructures, the compressive damage at high temperature was dominated by debonding of the interfaces between the primary NbSS and the 5–3 silicide, while the fracture mode at room temperature is transgranular, controlled by the primary NbSS cleavage.