Papers by Keyword: Ultrahigh Temperature Alloy

Abstract: The microstructure and mechanical properties including room temperature fracture toughness Kq, tensile strengthσb and elongationδ at 1250°C of the Nb based alloy directionally solidified in an electron beam floating zone melting (EBFZM) furnace have been evaluated. The microstructure is primarily composed of Nb solid solution (Nbss), α-(Nb)5Si3 and (Nb)3Si phases. After directional solidification with the moving rate of electron beam gun R being respectively 2.4, 4.8 and 7.2 mm/min, the primary Nbss dendrites, Nbss + (Nb)5Si3/(Nb)3Si eutectic colonies (lamellar or rod-like) and divorced Nb silicide plates align along the longitudinal axes of the specimens. When R = 2.4 mm/min, the best directional microstructure is obtained. Directional solidification has significantly improved theσb at 1250°C and Kq. The maximumσb occurs for the specimens with R = 2.4 mm/min and is about 85.0 MPa, meanwhile, the Kq is about 19.4 MPam1/2.

Abstract: The directionally solidified specimens of Nb-13.52 Si-22.60 Ti–6.88 Hf–2.54 Cr–2.24 Al alloy were prepared in an electron beam floating zone melting furnace at the withdrawing rate of 0.1, 0.3, 0.6, 1.0, 2.4 and 6.0 mm/min. All the primary Nb solid solution (Nbss) columns, Nbss + (Nb)3Si/(Nb)5Si3 eutectic colonies and divorced (Nb)3Si/(Nb)5Si3 plates or chains align well along the longitudinal axis of the specimens. With increasing of the withdrawing rate, the microstructure is gradually refined, and the amount of Nbss + (Nb)3Si/(Nb)5Si3 eutectic colonies increases. Both the room temperature ultimate tensile strength σb and fracture toughness KQ are improved for the directionally solidified specimens. The tensile fracture occurs in a cleavage way.