The effects of vacuum treatment and sintering atmosphere on mechanical properties of W-Ni-Fe heavy alloy have been studied. The compacts of 96W-2.8Ni-1.2Fe composition were sintered at 1460℃ for 1h under hydrogen atmosphere.
The sintered specimens were annealed at 400-1000℃ for "0" h in vacuum. In case of 600℃, the annealing time was extended to 3h.
The elongation of as-sintered specimens was about 7% at fracture with strain rate of 1 mm/min. By vacuum annealing at 700℃ and 800℃, the elongation was increased to about 15%. The highest elongation was obtained by vacuum annealing at 600℃ for 3h, and the mean value was 20%.
For some specimens, sintering atmosphere was changed to nitrogen from hydrogen during sintering cycle. When the atmosphere gas was changed at about 1000℃ during cooling from sintering temperature, the elongation was increased to 17%. But the elongation and the tensile strength was decreased when the atmosphere gas was changed at sintering temperature.
The tensile strength of the specimens showing low elongation was 800-900 MPa, and increased to 1000 MPa with increasing elongation value. The elongation of assintered specimens was decreased with increasing strain rate from 0.1 mm/min to 10 mm/min, but the tensile strength was increased.
It is suggested that the mechanical properties of W-Ni-Fe heavy alloy could be improved by vacuum treatment at 600-800℃ or, more efficiently, by changing atmosphere gas during the cool-down period of sintering. These improvements of mechanical properties are attributed to removing the hydrogen embrittlement effect by diminution of hydrogen content in the specimens.
