Microstructure and creep properties of a near-eutectic directionally solidified multiphase Mo-Si-B alloy

Due to their excellent creep behavior and acceptable oxidation resistance at ultrahigh temperatures multiphase Mo-based alloys are potential candidates for applications in aerospace engines and the power generating industry. The resulting materials properties, as well as the microstructure of Mo-Si-B materials, strongly depend on the manufacturing process. In the following paper we report on a new Mo-Si-B alloy which was processed by crucible-free zone melting (ZM) from cold pressed elemental powders. SEM investigations of the zone molten microstructure showed well-aligned arrangements of a three-phase microstructure consisting of a Mo solid solution (MoSS), and the two intermetallic phases Mo3Si and Mo5SiB2. First, high temperature mechanical properties, such as the compressive strength and creep strength at about 1100 °C, were evaluated and compared with a commonly used Ni-based superalloy and a PM processed Mo-Si-B material. In comparison to the PM processed reference alloy, the creep resistance of ZM materials was found to be substantially improved due to the relatively coarse directionally solidified microstructure. Thus, ZM alloys show great potential for applications at targeted application temperatures of around 1200-1300 °C.