Simultaneous improvement of microstructure and high-temperature tensile properties in CNT-doped Mo-based composites

Abstract

In this study, molybdenum–hafnium–carbon nanotube (Mo–Hf–CNT, MHC) composites are designed and fabricated using an efficient powder metallurgy method, involving wet dispersion, high-energy ball milling (HEBM) and spark plasma sintering (SPS). The optimal composites have submicrometric grains and nanoparticles uniformly dispersed at the grain boundaries and inside the grains. The composites are characterised using microstructure observations, tensile tests at room temperature and 500 °C as well as hardness tests after annealing at 800 °C-1400 °C. The composites exhibit excellent mechanical properties at 500 °C with an ultimate tensile strength of approximately 1.2 GPa and a total elongation of 15.6%. The MHC composite shows a simultaneous increase in the strength and ductility at 500 °C. Vickers hardness first increases and then decreases with the increase in temperature. The best overall performance is that of the Mo composite containing 2.0 wt % CNT/HfH2. In addition, the formation mechanism of the nanoparticles is discussed in detail. The simultaneous enhancement in the high-temperature strength and ductility can be attributed to the nanoparticles and planar slip. Therefore, this work provides a feasible way to fabricate high-performance Mo-based composites.