Research On The Cutting Performance And Wear Mechanism Of Multicomponent Coated HSS Tools

As an effective approach to improve performances of cutting tools, the technologies of coated tools have been rapidly developed and broadly applied. The multicomponent CrAlTiN coatings was deposited by using physical vapor deposition (PVD) coating techonlogy of closed field unbalance magnetron sputtering ion plating. The coating characteristics, cutting performances, wear mechanism and stress distribution of coated tools were studied.During determination of the coating characteristics, the coating surfaces and cross section were observed using scanning electron microscope (SEM) and transmission electron microscope (TEM). Results show that the multicomponent CrAlTiN coating matching with high speed steel (HSS) substrate is much more ideal and the coating microstructure is uniform and compact, by X-ray Diffraction (XRD) analysis, it is also found that the coating has gradient phases structure and composition along the thickness, as well as high thermal stability. By experimentations of indentation, scratch and Pin-on-Disc, the coating have many advantages including higher hardness and toughness, excellent anti-friction and wear performance and stronger bond with the substrate.A large number of turning and milling cutting tests were carried out with the multicomponent CrAlTiN coated HSS tools, the cutting perfomance were analyzed. The experimental results indicated that compared with the uncoated tools, the cutting performance of M2 HSS tools with multicomponent CrAlTiN coating is obviously improved, the cutting force is reduced, the cutting process becomes more smooth, the tools life is prolonged. With the mathematical statistics to handle the cutting force and tool life test data, the empiric formulae were built. Through analysis of tests curves and formulae, the rules are revealed which both cutting force and tool life change with cutting parameters.By observing wear regions of the tools, the worn surface morphology and the wear rule are analyzed with the multicomponent CrAlTiN coated HSS tools, results show that due to the existence of the coating, the worn surface morphology of coated tools is obviously different from the uncoated tools: The early wear stage of the coated tools is shorter, while the normal wear stage is longer; the coating is able to resist tool wear, but the effect of coating is different during each wear stage. The compositions of worn surface were analyzed by FESEM, and the wear mechanism of these coated tools were revealed. The analysis results show that there is some coating in the form of flakes on the abrasion area of rake face on the coated turning tools; oxidation wear of flank is severer than rake face; the oxidation wear and diffusion wear of the coated milling tool rake face is not significant, abrasive wear is the main reason; the spalling phenomenon on the coated milling tool flank is significant.The diagrams of von Mises equivalent stress distribution of coated and uncoated HSS tools wasw obtained through finite elements method simulation of the cutting process, the uncoated HSS tools illustrate the maximum von Mises stress on the rake face and near the tip of cutting edge.On the other hand, the coated HSS tools develop the maximum von Mises stress at a distance from the tip of the cutting edge, still on the rake face. The experimental results exhibit that the failed zone at initial wear stage fit the zone with the maximum Von Mises equivalent stress, it shows that mechanical stress is the main cause leading to early failure of coating.