Multiphase Mo-Si-B alloys processed by directional solidification

Abstract

Multiphase Mo-Si-B alloys are potential candidates for applications in the aerospace and power generation industry due to their enhanced creep and oxidation resistance at ultra-high temperatures. It is documented that the microstructure and the resulting properties of Mo-based alloys are heavily influenced by their fabrication procedure. In this study we investigate different multiphase Mo-Si-B alloys processed by zone melting (ZM) starting from cold pressed elemental powders. Microstructural characterization of zone melted alloys based on SEM investigations shows elongated arrangements of phases parallel to the growing direction as well as homogeneously distributed phases in the cross-section for some of the alloys investigated. First compression creep tests were performed at about 1100°C. In comparison to the creep resistance of powder metallurgically (PM) processed alloys the behaviour of ZM materials was found to be substantially improved. Hence, targeted application temperatures of around 1200°C to 1300°C may become feasible. Furthermore, the oxidation behaviour was found to be influenced by the volume fraction of the Mo solid solution phase since the volatilization of the Mo solid solution phase leads to a mass loss of the compound.