Development of Powder Metallurgy Based Metal Matrix Composites for Geothermal Applications

Abstract

Materials used in geothermal environment, depending on their location within the power plant, are subjected to several degradation mechanisms such as corrosion due to dissolved CO2, H2S, NH3 gases, sulphate and chloride ions, and erosion from the suspended solids in the geothermal fluid. Erosion-corrosion/erosion-wear is a major degradation mechanism for titanium based materials that are traditionally used to manufacture pumps for geothermal power plants. Metal Matrix Composites (MMCs) are a class of materials that can potentially have better erosion corrosion and wear properties compared to the traditional metallic alloys, and therefore, are of particular interest. In this study, we report our findings on the development of INCONEL625 (IN625) and Ti-6Al-4V (Ti64) base MMCs manufactured using powder metallurgy hot isostatic pressing (PM HIP). Ceramic powders with 10 vol.% of silicon carbide (SiC) and titanium diboride (TiB2) in IN625 and Ti64 powders, respectively, were blended and consolidated via PM HIP process. In-situ reactions occurred between the metal and ceramic phases in the MMC powders during consolidation, which resulted in the bulk specimens containing complex microstructures. It was found that the hardness of IN625 and Ti64 base MMCs more than doubled compared with HIPed IN625 and Ti64 alloys whilst the erosion-corrosion rate almost halved. Room temperature Charpy impact tests revealed that the mode of fracture was ductile, although a reduction in the ductility of the HIPed MMCs was observed.