Tribological performance of Diamond-Like Carbon and water-based lubricants for metalworking

Metalworking processes face challenges in extending tool life and eliminating harmful lubricants. This study investigates a new tribosystem that combines Diamond-Like Carbon (DLC) coatings and environmentally friendly water- based lubricants (WBL). The effects are analysed using tribological, machining, and sheet-metal forming. The first objective is to investigate DLC coatings on CNC lathe cutting tools under severe dry friction conditions. Machining was performed on Al6061 aluminum and AISI4340 alloy steel using double-layered (DLC/TiAlSN, DLC/CrN, DLC/TiAlN) and single-layered (TiAlSN, CrN, TiAlN) coatings. The test parameters include a depth of cut of 0.5 mm, a speed of 240 rpm, and a feed rate of 0.15 mm/rev. The results show the superior performance of the double-layered coating, with DLC/TiAlN excelling in cutting force, tool temperature, wear, surface quality, and chip thickness. Adhesive wear was found on machning aluminum, while abrasive wear was observed on alloy steel. The second objective evaluates the effect of additives in WBL. A hybrid additive system combining MXene and Ionic Liquid (IL) was formulated with Carboxyl Methyl Cellulose (CMC) and Xanthan Gum (XG) to improve viscosity and dispersion stability. Block-on-ring tribology tests (ASTM G77) at 500 rpm and 42 N revealed that XG improved WBL stability, while MXene/IL additives significantly reduced friction and wear. WBL formulated with CMC and MXene/IL hybrids were performed in hydrodynamic lubrication regime. The third objective was to evaluate the effect of the optimized DLC/TiAlN and WBL combination on sheet-metal forming in ironing process with 20% reduction thickness. Using DLC/TiAlN coated tools and SUS304 stainless steel sheets, ironing tests showed an 8% reduction in ironing force and less tool wear. Further tribology tests confirmed a 26% reduction in friction and a 7.3% reduction in wear. This study identified an optimal tribosystem, integrating DLC/TiAlN and CMC_MXene/IL, which improves lubricity, reduces wear and improves tool performance in metalworking applications

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