Hard turning using HiPIMS-coated carbide tools: Wear behavior under dry and minimum quantity lubrication (MQL)

In the present work, experimental investigations carried out to assess the applicability of HiPIMS (High Power Impulse Magnetron Sputtering)-coated carbide tools to hard turning (55 HRC) and to address the widely debated topic about the use of coolants in hard turning are presented. Tool wear progressions and hence, tool life, different tool wear forms and wear mechanisms observed for tools coated with HiPIMS coating technique, namely, nanocomposite AlTiN, nanocomposite multi-layer TiAlN/TiSiN and nanocrystalline AlTiCrN are presented along with the images captured by digital and electron microscope. Characterization results of all the coated tools in terms of their average coating thickness (measured using Calotest and Fractographs), adhesion strength of the coating(s) (determined using Scratch test), composition and microhardness (using EDAX and Vickers microhardness test, respectively) are presented. Experimental observations indicate higher tool life with nanocrystalline AlTiCrN coated carbide tools which shows encouraging potential of these tools to hard turning. Improvement in tool life of almost 20-25% has been observed under minimum quantity lubrication (MQL) due to better cooling and lubricating effects. However, this effect was more prominent at higher cutting speed of 150 m/min.