Mechanical alloying process of 93W-5.6Ni-1.4Fe tungsten heavy alloy

Abstract

The mechanical alloying process of 93W-5.6Ni-1.4Fe tungsten heavy alloy from the elemental powders of W, Ni and Fe by a high energy ball mill in argon atmosphere was investigated. The mechanical alloying process parameters such as milling speed, milling time, ball-to-powder ratio and ball filling ratio were varied in order to investigate their influence on the microstructural evolution of mechanically alloyed powders. The mechanical alloying process proceeded following five distinct stages such as flattening stage, welding dominant stage, equiaxed particle forming stage, random lamellar forming stage and steady state stage with increasing the milling time. The steady state stage of mechanical alloying was reached after milling for 48 hours with milling speed of 75 rpm, ball-to-powder ratio of 20:1 and ball filling ratio of 15%. Nanocrystalline grain size of 16 nm was obtained at the steady state stage of mechanical alloying. Mechanically alloyed powders were consolidated by cold isostatic pressing and followed by sintering at temperature ranged 1300-1485 degrees C for 1 hour in hydrogen atmosphere. When liquid phase sintered at 1485 degrees C, tungsten heavy alloy from mechanically alloyed powders showed finer tungsten particles about 27 mu m than that from conventionally blended powders. The density of liquid phase sintered tungsten heavy alloy decreased with increasing the milling time due to the swelling during sintering. When solid state sintered below 1430 degrees C, tungsten heavy alloy from mechanically alloyed powders showed ultra-fine tungsten particles about 3 mu m and showed high relative density above 97% insensitive to the milling time.