Property-Microstructural Relationship in a Tungsten Heavy Alloy

Tungsten Heavy Alloys (WHA) have been used as vibration dampeners and balance weights in aerospace applications for a number of years.  While the WHA have been used mostly as “dumb” masses this class of materials can posses widely varying mechanical properties depending on their processing history.  In particular the role of tungsten grain size can greatly influence static and dynamic mechanical properties.  In this paper the relationship between sintering, heat treatment and deformation processing and mechanical properties has been investigated for a 93 weight percent tungsten alloy.  Sample geometry pieces were liquid phase sintered at two different temperatures in order to vary the tungsten grain size.  These sintered samples were then deformed to a strain of 19% in order to further modify the grain size.

 

The resulting tensile and impact properties show a decrease in all properties as the tungsten grain size increases, except in the case where the material did not undergo complete liquid phase sintering.  In this case the properties were lower than any sample that had a mature microstructure.  Scanning electron micrographs of the fracture surfaces revealed that no major change was seen in the fracture path of the sintered alloys.  This indicated that the change in properties was solely related to the microstructural variation.

 

When the material is subject to a 19% strain the ultimate tensile and yield strength exhibit a significant increase while a decrease in ductility and impact properties is seen.  The resulting properties are due to the work hardening of the WHA and near recovery of the pre-strained properties are possible with a solutionizing heat treatment.  The elongation of the tungsten grains, due to deformation, was shown to have an effect on the impact properties of the alloy even after heat treatment.