발간논문

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Vol.15, No.2, 208 ~ 210, 1977
Title
윤영섭 , 윤덕용
Abstract
The effect of cold working and subsequent annealing on mechanical properties of W-Ni-Fe heavy alloy has been studied. The specimen composition was 90W-5Ni-5Fe by weight percent. The specimens were prepared by usual powder metallurgy techniques and sintered in liquid phase at 1460℃ for 30 minutes in hydrogen atmosphere. The specimens were then cold worked up to 60% by rolling. The observed UTS increases with cold working from about 94㎏/㎟ to 143㎏/㎟ at 50% deformation. The elongation decreases sharply from 20% to about 2% at 15% deformation. While the microhardness of the tungsten grains increases steadily with degree of cold work, the micro hardness of the matrix appears to increase rapidly with deformation initially. It is therefore suggested that at relatively small deformation the matrix phase work hardens rapidly and affects the deformation behavior of the composite alloy. The alloy specimen cold worked to 50% was annealed at temperatures from 400℃ to 1000℃ for an hour in hydrogen atmosphere and the mechanical properties were measured. Annealing of the cold worked specimen at 400˚increases UTS to 160㎏/㎟ from 143㎏/㎟ for the unannealed specimen, and with increasing annealing temperatures UTS decreases. The elongation begins to increase with annealing temperature at 800℃ and rises sharply to 4% at 1000℃. The microhardness of the tungsten grains remains unchanged with annealing temperature up to 600℃ and from 800℃ begins to decrease slowly. The microhardness of the matrix on the other hand shows maximum after annealing at 400℃ and decreases subsequently with higher annealing temperatures. These observations indicate that the increase of the UTS after annealing at 400℃ is largely due to the increased strength of the matrix. This increase in matrix strength with annealing is most likely caused by some, kind of precipitation hardening which is probably accelerated by cold work. The observed changes of mechanical properties at higher annealing temperatures are attributed mainly to the recovery and recrystallization of the matrix phase.
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