Effect of gas bubbles on recrystallization of tungsten

Abstract

Tungsten sheet deposited from WF6 vapor was rolled at temperatures up to 1000°C and reductions in thickness up to 95 pct. Recovery and recrystallization were studied using hardness measurements and transmission electron microscopy. The temperatures for the onset of recrystallization during 1 hr anneals were 1600°C or more. Recrystallization was sluggish, requiring temperatures of 2100°C or more for completion. Transmission electron microscopy revealed that many small (< 500A diam) gas bubbles were present on dislocations and recovered subgrain boundaries and caused scalloping of these boundaries and the advancing recrystallized grain boundaries. Coarsening of the bubbles to a relatively few larger bubbles permitted complete recrystallization. No solid inclusions were found. Annealing treatments that coarsened the gas bubbles prior to rolling caused accelerated recovery and complete recrystallization was observed at approximately 1200°C. It is concluded that small gas bubbles were the cause of the original high recrystallization temperatures and also influenced the size and shape of the recrystallized grains.