Effects of sintering conditions on mechanical properties of mechanically alloyed tungsten heavy alloys

Abstract

The effects of sintering conditions on microstructural evolution and mechanical properties of mechanical alloyed tungsten heavy alloy were investigated. W, Ni and Fe powders were mechanically alloyed in a tumbler ball mill with milling speed of 75 rpm, ball-to-powder ratio of 20:1 and ball filling ratio of 15%. Mechanically alloyed powders were compacted and solid state sintered at 1300 degreesC for I hour in hydrogen atmosphere. The solid state sintered tungsten heavy alloy was subsequently liquid phase sintered at 1470 degreesC with varying the sintering time from 4 min to 90 min. The solid state sintered tungsten heavy alloy showed fine tungsten particles of 3 mum in diameter and high relative density above 99%. The volume fraction of matrix phase was measured as 11% and tungsten/tungsten contiguity was 0.74 in solid state sintered tungsten heavy alloys. Two-step sintered tungsten heavy alloys showed finer tungsten particles of about 6-15 mum and volume fraction of matrix phase of 16% and tungsten/tungsten contiguity of 0.40. The solid state sintered tungsten heavy alloy exhibited yield strength about 1100 MPa due to a finer tungsten particles, while showed low elongation and impact energy due to a large tungsten/tungsten contiguity. The yield strength of two-step sintered tungsten heavy alloys increased with decreasing the tungsten particle size and volume fraction of matrix.