The effects of cryogenic cooling on tool wear and chip morphology in turning of tantalum-tungsten alloys Ta-2.5W

Tantalum‑tungsten alloy is particularly difficult to cut due to its high plasticity. Environmentally friendly liquid nitrogen cooling and hybrid minimum quantity of lubricant-low temperature CO₂ (MQL + CO₂) technology can improve the machinability of ductile materials. In this paper, the experimental and numerical turning of tantalum‑tungsten alloy Ta-2.5W were carried out under cryogenic cooling conditions. The effects of liquid nitrogen cooling and MQL + CO₂ cooling on the wear mechanism of cutting tools and the formation mechanism of chips were studied. The Rehbinder effect induced by the surfactant in MQL + CO₂ system was analyzed. The results show that the cutting tool life can be effectively improved by 50 % in turning of Ta-2.5W under both cryogenic cooling conditions. Different from the flank wear dominated by adhesive wear under water-based emulsified cutting fluid, the tool failure was mainly caused by the notch wear under cryogenic cooling conditions. The chips in turning of high plastic Ta-2.5W showed a “pomelo-meat shaped” morphology with non-uniformed and non-periodic folds. Rehbinder effect was induced by the surfactant in MQL + CO₂ system, which transformed the “pomelo-meat shaped” chips into “layered-rock shaped” chips. Under this effect, the machinability of tantalum‑tungsten alloy was effectively improved with a reduction of chip thickness and increment of the tool life.