Effect of machining operations on mechanical properties, surface integrity and corrosion resistance of tungsten heavy alloy

Abstract

Tungsten heavy alloys (WHAs) are metal-metal matrix composites which are suitable candidates for defence and nuclear applications. In order to meet the geometric complexity and dimensional tolerance of products made with these WHAs, secondary machining operations are necessary. The effect of three set of machining operations (wire EDM, rough turning and finish turning) on mechanical properties, surface residual stress, surface and sub-surface hardness and corrosion resistance are explored in this work. Uniaxial tensile test specimens were prepared with two different sets of feed rate and depth of cut corresponding to rough and finish turning. For the specimens prepared with harsher conditions around 20% reduction in elongation was noticed though there were no significant changes in yield strength or ultimate tensile strength. Finish turning resulted in a surface residual stress in the order of 700 MPa, compressive in nature. Though compressive, the magnitudes of the surface residual stress were significantly reduced for the other two operations. Turning operations were found to work harden the surface while WEDM caused a reduction in surface hardness. Subsequent variations in the subsurface hardness were also observed reaching upto a depth in the range of 50–150 µm. Surfaces produced under different machining conditions were exposed to chloride solution to examine the impact of surface integrity on the corrosion behaviour and the correlation among the two are investigated. Rough turned surfaces and wire EDM surfaces have shown reduced corrosion resistance.