Quantitative Evaluation of Microstructure in Mo-Si-B-TiC Alloy Produced by Melting and Tilt Casting Methods

Abstract

Mo-Si-B-TiC alloys are expected to be a candidate for an ultrahigh-temperature material beyond Ni-base superalloys. This work quantitatively investigated the microstructure of a Mo-Si-B-TiC alloy with the composition of Mo-5Si-10B-10TiC (65Mo alloy) (at%) produced via arc-melting and tilt-casting techniques. The alloy was composed of four constituent phases: Mo solid solution (Mo_ss), Mo₅SiB₂(T₂), (Ti, Mo)C_x, (Mo, Ti)₂C, and their eutectic (or peritecteutectic) phases. The compositions of the constituent phases were determined by electron beam micro analyzer (EPMA). Scanning electron microscopy – backscattered electron diffraction (SEM-EBSD) measurements revealed that T₂ and (Ti, Mo)C_x phases have orientation relationships with Mo phase: {110}_Mo//(001)_T2, <111>_Mo//<001>_T2 and {110}_Mo//{111}_(Ti,Mo)Cx, <111>_Mo//<001>_(Ti,Mo)Cx. Furthermore, the three-dimensional SEM observation with the combination of the focused ion beam (FIB) serial sectioning technique demonstrated that the T₂ phase had a thin plate shape with the orientation of (001) as plate surfaces and of {100} as side ones.

Fig. 10 Three-dimensional phase images reconstructed from serially-sectioned images: (a) (Ti, Mo)C_x and T₂ (Mo₅SiB₂), (b) (Ti, Mo)C_x, (c) T₂.