Evaluation of Thermal, Fracture, and High Temperature Behavior of Mechanically Alloyed and Spark Plasma Sintered Nano-Y2O3 Dispersed W-Ni-Mo and W-Ni-Ti-Nb Alloys

Tungsten (W), Nickel (Ni), Molybdenum (Mo), Niobium (Nb), Titanium (Ti) based W-Ni-Mo and W-Ni-Ti-Nb alloys with nano-yttrium oxide (Y2O3) dispersion and nominal compositions of W79Ni10Mo10(Y2O3)(1) (Alloy A) and W74Ni10Ti5Nb10(Y2O3)(1) (Alloy B) (all in weight percent) were fabricated by mechanical alloying and spark plasma sintering (SPS) at 1,000 degrees C, 1,200 degrees C, and 1,400 degrees C for 5 min with 75 MPa pressure. The thermal behavior of milled powders and microstructure evolution of milled and consolidated products were examined by scanning electron microscopy, energy-dispersive spectroscopy, and high-resolution transmission electron microscopy. The activation energy of recrystallization for Alloy B is higher as compared to the recently investigated oxide dispersion-strengthened tungsten alloys. The mode of fracture is predominantly intergranular with a titanium addition. Alloy A SPS at 1,400 degrees C shows superior oxidation resistance at 1,000 degrees C as compared to Alloy B at the identical SPS temperature (1,400 degrees C), owing to a higher intensity of the protective nickel tungsten tetroxide, yttrium tungstate oxide scale formation, and less variation in the molar volume of formed oxides.