Microstructure and mechanical properties of mechanically alloyed tungsten heavy alloys

Abstract

The effects of mechanical alloying process conditions on the microstructure of 93W-5.6Ni-1.4Fe heavy alloys were investigated. Elemental powders of tungsten, nickel and iron were mechanically alloyed in a tumbler ball mill. The microstructural observation of mechanically alloyed powders indicated that the mechanical alloying process proceeded into five distinct stages, such as initial stage, welding dominant stage, equiaxed particle forming stage, random lamellar forming stage and steady state stage. The microstructure of mechanically alloyed powders became fully homogeneous with fine lamellar spacing less than 0.2 ㎛ and average grain size of 16 nm in a steady state stage. The average grain size was 16nm in the steady state stage. The effects of milling parameters such as ball-to-powder ratio and ball filling ratio were investigated by comparing parametric modeling with microstructural observation of mechanically alloyed tungsten heavy alloy powders. Mechanically alloyed powders were consolidated into green compacts and solid state sintered or liquid phase sintered at various conditions in order to control the microstructures. The solid state sintered tungsten heavy alloys using mechanically alloyed powders showed fine tungsten particles about 3 ㎛ and high relative density above 99%. Solid state sintered tungsten heavy alloys were subsequently liquid phase sintered at a temperature of 1470℃ with varying liquid phase sintering time from 4 min. to 90 min. Two-step sintered tungsten heavy alloys using mechanically alloyed powders showed tungsten particles of about 6-15 ㎛ finer than those of 30-40 ㎛ in conventional liquid phase sintered tungsten heavy alloys. Tungsten heavy alloys with inhomogeneously distributed matrix pool were fabricated by partial mechanical alloying which consist of mechanical alloying of matrix composition 30W-56Ni-14Fe and followed by mixing of mechanically alloyed 30W-56Ni-14Fe powders with balanced amount of tungsten powders. Oxide dispers...