Assessment of a powder metallurgical processing route for refractory metal silicide alloys

Abstract

A powder metallurgical (PM) processing route for the manufacturing of two different refractory metal silicide alloys comprising inert gas atomization of presintered bars, hot isostatic pressing, and hot extrusion (reduction in cross section of 6:1) was established. The mechanical properties between room temperature and 1200 °C of the PM-processed Mo-3Si-1B and Nb-24Ti-20Si-5Cr-3Hf-2Al alloys (in wt pct) were assessed with tensile tests vs a state-of-the-art Ni-base single crystalline alloy (CMSX 4) and a directionally solidified (MASC) niobium-base silicide alloy, respectively. The microstructural characterization of both the hot-isostatically pressed and extruded materials was carried out applying scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD) analysis. The Mo-Si-B alloy is characterized by an intermetallic matrix surrounding globular Mo particles in the hot isostatic press and a nearly continuous molybdenum solid solution matrix with dispersed intermetallic particles in the hot-extruded condition. Hot extrusion results in a substantial reduction of the DBTT of about 200 °C and tensile strengths superior to CMSX 4 at temperatures above 1000 °C. In the case of the Nb-base silicide alloy, a niobium solid solution surrounding intermetallic particles with Nb5Si3-type structure characterizes the final alloy. In the intermediate temperature range of 500 °C to 816 °C, a strength level equivalent to the directionally solidified MASC alloy was observed.