Research on the Preparation of low-oxygen, high-density and ultra-fine grained Mo Metal by a Two-step Method of “Hydrogen Deoxidation Pre-sintering + Spark Plasma Sintering”

In this work, ultrafine Mo powder (0.4 μm) was used as the raw material, and a two-stage sintering method composed of deoxidation pre-sintering and Spark Plasma Sintering (SPS) was employed to prepare fine-grained and high-strength Mo metal. The oxygen content decreased from 0.237 wt% of the Mo powder to 0.066 wt% after pre-sintering in H2 at 1000 °C for 2 h. It was found that a large number of sintering necks were formed in the pre-sintered skeleton, and the grain size did not increase significantly. Then, the pre-sintered skeleton was sintered by SPS at 1200 °C with a pressure of 50 MPa for 10 min. The Mo skeleton was sintered and the relative density of the product reached 99.2%. Due to the relatively low SPS sintering temperature (1200 °C), the average grain size was 0.88 μm, which is not grow significantly. Benefiting from the low oxygen content, high relative density, and small grain size, the Vickers hardness and bending strength of the Mo metal prepared in this work were 300 HV and 523 MPa, respectively. However, increasing the temperature to 1100 °C makes it difficult to sinter the sample, and the relative density is only 91.3%, and the Vickers hardness and bending strength decreased to 215 HV and 343 MPa, respectively. Increasing the SPS sintering temperature to 1300 °C caused the grain size to increase significantly to 6.95 μm, and the Vickers hardness and bending strength decreased to 197 HV and 467 MPa, respectively.