A novel approach to boriding of TZM by spark plasma sintering method

Boriding can be candidate method to increase mechanical properties and oxidation resistance of molybdenum based alloys. Rapid oxidation of TZM at elevated temperature and low wear resistance are considered to be main drawbacks for possible applications. In this study molybdenum boride layer was formed on the surface of TZM by spark plasma sintering (SPS) method. Pre-mixed TZM was used as a raw material in powder form. Both sintering and boriding process were performed in a single step at constant temperature of 1420 °C in various pressures (40–60 MPa) and holding times (5–15 min) under vacuum. The effects of molybdenum boride layer on density, hardness and oxidation behavior were investigated. Thickness, microstructure and hardness of Mo-B based protective layer showed a variety with different process parameters. The boride layer thickness was reached to approximately 200 μm by increasing pressure and holding time. Formation of this layer provided a decrease in mass loss about 73.4% during oxidation test at 1000 °C for 60 min. The maximum surface hardness value was obtained as 21.4 GPa while hardness of base metal was 2.3 GPa.