Processing, Microstructure and Mechanical Properties of Mechanically Alloyed Tungsten Heavy Alloy

摘要

93W-5.6Ni-l.4Fe tungsten heavy alloys were fabricated by mechanical alloying process to control the microstructure and mechanical properties. The mechanical alloying process proceeded through blending stage, cold welding stage, equiaxed particle forming stage, random welding stage and steady state stage. The mechanically alloyed powders showed nanocrystalline grains of about 16 nm and lamellar spacing of about 200 nm. Tungsten particle size can be refined up to 3 μm with full densification after solid-state sintering. Tungsten particle size can be controlled in the range of 6-15 μm with varying secondary sintering temperature and time in two-step sintering process. Oxide dispersion strengthened tungsten heavy alloy containing 0.1-5wt% Y_2O_3 particles can be obtained and oxide particles effectively reduce the coarsening rate of W particles during sintering. Yield strength increases as the W particle size decreases as explained in the Hall-Petch type relationship as a function of tungsten particle size and matrix volume fraction. High temperature compression test of tungsten heavy alloy at 800°C showed that the strength of mechanically alloyed ODS tungsten heavy alloys increased with the oxide content. The fractographies of solid-state sintered tungsten heavy alloy showed tungsten/tungsten debonding, two-step sintered tungsten heavy alloy showed mixed fracture modes and liquid-phase sintered tungsten heavy alloy showed tungsten cleavage after tensile tests.