Toughness and strength characteristics of Nb-W-Si ternary alloys prepared by Arc melting

• DOI: 10.1007/s11661-003-0187-9
• Publication Date: 2007-04-16T09:27:13Z
• Authors: Jiangbo Sha; Hisatoshi Hirai; Hidetoshi Ueno; Tatsuo Tabaru; Akira Kitahara; Shuji Hanada
• Keywords: 02 engineering and technology; 0210 nano-technology

This article describes the room-temperature and high-temperature mechanical properties and failure modes of series Nb-W-Si alloys—Nb-10W, Nb-10Si, Nb-10Si-5W, Nb-10W-5Si, and Nb-10W-10Si—prepared by arc melting. For the Nb-10W alloy, the microstructure was a monolithic Nb solid solution (Nbss) with a grain size up to a few hundred microns, while the other four alloys consisted of primary Nbss and a eutectic of Nbss/Nb5Si3 (5-3 silicide) as a result of replacing Nb with Si. Among all alloys, the Nb-10W showed the highest fracture toughness of about 15.3 MPa√m1/2 and the lowest 0.2 pct yield compressive strength of 90 MPa at 1670 K. Conversely, the Nb-10Si-10W had the highest 0.2 pct yield strength of about 330 MPa at 1670 K and the lowest fracture toughness of 8.2 MPa√m1/2. It is suggested that toughness is supplied by the metallic Nbss phase, while high-temperature strength is mainly provided by the brittle silicide phase. For the Nb-10W alloy with the monolithic Nbss, intergranular cleavagelike crack propagation is the fracture mode at room temperature, and dislocation movement within the grains and grain-boundary sliding are the dominant modes of high-temperature failure. With two-phase Nbss/Nb5Si3 microstructures, the compressive damage of all four alloys at high temperature was dominated by debonding of the interfaces between the Nbss and the silicide; however, the fracture mode at room temperature is transgranular, controlled by the primary Nbss cleavage.