Performance Evaluation of PVD and CVD Multilayer-Coated Tools in Machining High-Strength Steel

To curtail the negative effects of traditional flood machining, dry cutting using carbide tools has emerged as a prominent alternative for manufacturers, owing to its low cost and phenomenal surface qualities. In line with this view, high-speed machining of high-strength AISI 4340 alloy steel was carried out using multilayer Al2O3/TiCN-CVD and TiAlN/AlCrN-PVD carbide tools in a dry environment. The experimental scheme was adopted, as per Taguchi’s L18 orthogonal array, to investigate the two most crucial machinability aspects, namely tool life and surface roughness. An analysis of variance (ANOVA) was performed on the obtained data, and it was inferred that the feed rate exhibited the strongest effects on both the tool life and surface roughness, with corresponding percentage contributions of 46.22% and 68.96%, respectively. The longest tool lives of 14.75 min and 10.08 min were obtained at a low cutting speed and feed rate for CVD and PVD tools, respectively. However, the lowest surface roughness of 0.276 µm and 0.307 µm was achieved at a high cutting speed and low feed rate for PVD and CVD tools, respectively. The evolution of tool wear, studied through the microscopic images of the worn tools, revealed that a high cutting speed and feed rate accelerated the flank wear for both types of tools. Nevertheless, the CVD tool exhibited better results due to the thick and effective Al2O3/TiCN coating layer, which protected the carbide substrate against thermal–mechanical loads. Moreover, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) performed on the worn tools revealed that adhesion, oxidation, diffusion, and abrasion were the main wear mechanisms for both types of tools.