Production of B₄C reinforced TZM alloy and boriding its surface in one step by spark plasma sintering (SPS)

TZM alloy is one of the most important Mo-based alloys that has been used for high temperature applications due to its high melting point, good thermal conductivity and low thermal expansion coefficient. However, low oxidation resistance at elevated temperatures limits the high temperature applications of TZM. In this study, B₄C reinforced TZM alloy was produced and its surface was borided in one step with spark plasma sintering (SPS) method. Homogeneously mixed TZM + B₄C powders were molded between B₄C powders and both sintering and boriding process were performed in a single step at different pressure and holding times. The effects of sintering parameters on densification, phase formation, microstructure, hardness and oxidation behavior were investigated. The thickness of the Mo–B based protective layers varied from 215 to 430 μm depending on holding time and pressure. Boride layer of all samples had a lower hardness value than the matrix due to porosity formation near the surface. The hardness of the boride layers varied from 5.1 to 16.1 GPa depending on the amount of porosity. The highest hardness value was measured as 17.2 GPa on the matrix of TZM5B-10-70. Mo₂B-Mo₂C based matrix formation and Mo–B based protective layer improved the oxidation resistance of TZM alloy by reducing mass loss caused by exposed Mo.