Performance of new cutting tool multilayer coatings for machining Ti-6Al-4V titanium alloy under cryogenic cooling conditions

Cr/CrN/AlCrN multilayer coatings were recently developed to meet the high challenges of machining Ti-6Al-4V alloy under cryogenic cooling conditions. The multilayer coatings were optimized by multiple deposition conditions and were characterized by multi-methods. It was proved that they are suitable for tribological applications with this alloy under extreme conditions. This paper addresses the performance of these coatings through tool wear tests and analysis. This performance was compared with that obtained in standard machining conditions used in the aerospace industry, which include flood metalworking fluids and uncoated cemented carbide tools. The results show that the application of a multilayer coating can improve significantly the tool life under cryogenic cooling conditions compared to the flood conditions. 33 % improvement of tool life was found under cryogenic cooling conditions when comparing this coating to the uncoated one. A statistical analysis shows a strong correlation between tool wear and the machining forces. This analysis also permitted to build models for predicting tool wear in function of measured forces.