Influence of processing on the microstructure and mechanical behaviour of Mo-Si-B alloys

Mo-Si-B materials consisting of a Mo(Si) solid solution and the intermetallic phases Mo3Si and Mo5SiB2 (T2) were prepared by mechanical alloying (MA) as the crucial step of a powdermetallurgical process. After consolidation via an industrial processing route (cold isostatic pressing, sintering, hot isostatic pressing) the resulting microstructures of Mo-Si-B alloys up to 45% of intermetallic phases reveal a continuous α-Mo matrix with embedded, homogeneously distributed intermetallic particles. Clearly, increasing the amount of Mo solid solution reduces the BDTT (demonstrated by three point bending tests between room temperature and 12000C), however, values below 9000C could not be obtained due to grain boundary embrittlement caused by Si segregation. Alloying with Zr was proven by Auger analysis in Mo-Si solid solutions to reduce this segregation. Therefore, in a second trial Zr as a (micro-) alloying element was added. The influence of microalloying on ductility and strength is comparatively discussed with reference compositions Mo-6Si-5B and Mo-9Si-8B.