Effect of Micro-blasting on Characteristics and Machining Performance of PVD AlTiN Coated Cutting Tools

Abstract

It is essential to sustain ever increasing challenges faced by cutting tool manufacturers in improving the performance of the tools during machining of difficult-to-cut materials which have been developed in recent times. Although coated tools have found wide application in industries, there still remains a considerable scope of improvement of the properties of coatings with a view to achieve environment-friendly dry machining. Surface treatment has been identified as one of the possible avenues which has the potential to augment properties and performance of coated tools in dry machining. The current research work has utilized micro-blasting of cutting tool substrates prior to coating deposition as well as coated surface in order to recommend optimal surface treatment technique for the development of a coated tool. AlTiN coating is deposited using cathodic arc evaporation and effect of micro-blasting both as pre-treatment as well as post-treatment methodology is investigated on micro-structure, crystallographic orientation, grain size, coating adhesion and hardness. Effect of surface treatment has been finally studied during machining of 17-4 PH martensitic stainless steel. As-deposited AlTiN coating without any treatment has all along been considered for comparison. Results have clearly indicated micro-blasting as pre-treatment technique considerably enhances coating adhesion while post-treatment results in increase in hardness. Since both the properties are essential in combating coating delamination and improving wear resistance, AlTiN coating with both pre- as well as post-treatment techniques has demonstrated excellent promise in dry machining application. Significant reduction in cutting force up to 27% is observed using AlTiN coated tool subjected to both pre- and post-treatment. The same tool is also successful in bringing down in chip reduction co-efficient. While tool wear progression of only pre-treated and pre- as well as post-treated tools are similar under lower cutting speed (120 m/min), the latter clearly outperformed all the tools under higher cutting speed (150 m/min).