The present study aims to extend the life of tungsten carbide (WC) cutting tools utilized in face milling operations of Ti-6Al-4V by applying hard protective coatings developed using the cathodic-arc physical vapor deposition (CAPVD) technique. Box-Behnken design with 15 experimental runs and response surface methodology were used to mathematically model the relationships between input parameters and output responses to determine the optimal cutting parameters resulting in maximum material removal rate and minimum tool wear. Additionally, the performance of uncoated and coated carbide tools was assessed under dry and wet conditions to identify the best machining conditions. Intriguingly, the tool life of an uncoated WC tool in dry conditions was up to threefold more than that in wet conditions. The tool life of the coated tools was 33% to 166% longer than that of their uncoated counterparts. An analysis of their performance revealed an inverse relationship between the amount of Al in the coating and the tool life. The results from sliding wear tests suggest that Al-deficient coatings have a low coefficient of friction. This study sheds light on the effectiveness of CAPVD-coated carbide tools for improving the tool life during face milling of Ti-6Al-4V.

The present study investigates the influence of substrate bias on edge-rounding of TiAlN-coated drill bits arising out of coating deposition and the resulting cutting performance while machining Inconel 718. Tungsten carbide (WC) drill bits were deposited with TiAlN coating through a cathodic arc physical vapor deposition (CAPVD) system. Five different substrate bias voltages varying from -20 V to -60 V were employed for the deposition. The hardness, adhesion strength, and residual stress were significantly influenced by substrate bias. The sharp edges of coated drill bits exhibited significant edge-rounding at relatively higher levels of substrate bias. The reason for such edge-rounding is the re-sputtering and residual stress-induced micro-chipping of the previously formed coating layer during the deposition. The edge-rounding of drill bits was in the order of: 20 V <30 V <40 V <50 V <60 V. The drill bits deposited at -50 V substrate bias exhibited the best tool life owing to optimum edge radius (resulting in better edge stability) and coating properties. The present study helps identify an optimum level of substrate bias, which results in a favorable edge radius and the best tool life of the coated drill bits.

The ever-increasing demand for cost-effective machining of Ni (Nickel) based superalloys has made it necessary to explore nanocomposite coatings as a potential surface engineering solution. The present study aims to investigate the variation in machining performance of new-generation hard wear-resistant coatings in milling of IN 718 (Inconel 718), IN 625 (Inconel 625), and IN 617 (Inconel 617). TiAlSiN and CrAlSiN coatings were grown in-house over tungsten carbide (WC) milling inserts through the cathodic-arc PVD route. The TiAlSiN coating improved the tool life by 80% and 60% in the case of IN 718 and IN 625, respectively. However, in the case of IN 617, the TiAlSiN-coated tool could not even reach the uncoated tool life. The CrAlSiN coating, on the other hand, improved the tool life by more than 200% in the milling of IN 617. Tool-chipping was the dominant failure mode among all observed, which included flank wear and workpiece adhesion. The repeated adhesion and removal of the workpiece layer from the tool surface was a major cause of tool failure. The coating layer delayed the initiation of the chipping and prolonged the flank-wear-dominated machining time, resulting in improved tool life. The wear resistance of coatings in machining different workpiece materials was greatly influenced by the relative affinity of constituting elements of workpieces for employed coatings. The machining chips exhibited shear bands and saw-tooth (serrated/segmented) morphology in almost all cases. The degree of segmentation showed a direct correlation with tool life.The present work helps identify the optimum coating and machining conditions for three different grades of Ni-based superalloys. Additionally, the underlying mechanisms were analyzed and discussed with scientific observations.

The study investigates the performance of TiN and TiAlN coated carbide tools to improve the tool life in the limited explored drilling operation of difficult-to-cut Inconel 718 (IN 718). We deposited these coatings over tungsten carbide (WC) drill bits through the cathodic arc PVD route and evaluated their tool life at optimized machining parameters. Tool wear initiated with chipping at the corner of the margin and cutting edge (periphery wear), followed by coating abrasion and flank wear. In the case of TiAlN coated drill bit, we observed a notable built-up edge (BUE), indicating adhesive wear, which is not distinctly noticeable in the case of TiN coated drill bits. The comparison of the associated machining challenges between IN 718 and relatively softer EN 24 revealed no chipping but a significant built-up edge in the case of EN 24. At optimized machining parameters of 800 rpm spindle speed and 30 mm/min feed rate, TiAlN and TiN coated drill bits performed 2 and 1.6 times, respectively, better than uncoated drill bits in terms of the number of holes drilled. In addition, the performance of commercially available TiAlN coated drill bits was also compared with that of TiAlN coated drill bits produced in the present study by employing identical machining conditions. The in-house TiAlN coated drill bits yielded 50% additional life than the commercially available TiAlN coated drill bits. Additionally, the machined surface of drilled holes with TiAlN coated drill bits resulted in lower roughness (Ra) than the uncoated drill bits at the end of the respective tool life. The underlying reasons were analyzed and discussed.

Abrasive wear of biomass briquetting machine components, such as shedder blades, hammer blades, dies and rams, etc., is the primary limiting factor that affects the economic viability of the biomass briquetting process. In order to overcome this issue, attempts were undertaken in this work to evaluate the applicability of commercially well-established Ti-based metal nitride wear-resistant coatings to reduce abrasive wear. The TiN, TiCrN, and TiAlN coatings were deposited on D3 hard steel using the cathodic arc physical vapor deposition technique. A dry sand rubber wheel tester was used to assess the abrasive wear characteristics of the coatings and bare D3 hard steel. Coating properties, such as hardness, adhesion strength, surface roughness, and residual stress, were also evaluated. The results demonstrated that coating defects (microdroplets and pull-outs/craters), coating hardness, and elastic modulus play a major role in abrasive wear performance. The TiCrN coating has shown the highest abrasion resistance due to high H3/E2 ratio compared to other coatings. The abrasive wear mechanism of the TiAlN coating majorly followed coating spallation due to high compressive residual stress and low adhesion strength. The TiN coating exhibited the worst abrasive wear resistance among the three coatings due to localized ploughing at coating microdroplet and crater sites. Therefore, based on the results, the TiCrN coating has the potential to enhance the service life of briquetting machine components by orders of magnitude compared to uncoated ones