Study On The Preparation And Properties Of PVD Coatings On TiCN-based Cermets

TiCN-based cermet is a new type of tool material developed by using relatively abundant Ti and Ni to avoid excessive dependence and consumption of W and Co strategic resources in traditional cemented carbide tools,with the characteristics of low density,low friction coefficient,high hardness,high wear resistance and high temperature resistance.Since the TiCN-based cermet is the same as the cemented carbide,the structure contains a large amount of metal binder phase.During cutting,the metal binder phase in the tool and the material to be processed are easily bonded,which affects the processing quality.Besides,the metal binder phase is easily softened at high temperature,which reduces the hardness,strength and wear resistance of the tool,resulting in rapid tool wear and shortened life.Therefore,it is an important trend in the development of cermet tools in the future to improve the performance and extend the life of TiCN-based cermet tools by surface coating treatment.As a high-quality and environmentally friendly tool coating technology with low deposition temperature and good controllability of coating composition and structure,physical vapor deposition(PVD)technology is widely used in cemented carbide and high-speed steel tools.However,the PVD coating technology on the surface of TiCN-based cermet tools is not mature,and there is no unified understanding of the effect of coatings on cermet tools at home and abroad.Moreover,the effect of the growth pattern of coating deposition atoms on the cermet substrate,the chemical composition of TiCN-based cermet,surface state and deposition conditions on the nucleation and growth,microstructure and properties of the coating,and the failure mode and mechanism of the coated TiCN-based cermet tool under cutting conditions are still unclear.In this paper,arc ion plating and evaporation plating were used to prepare PVD coatings on the surface of TiCN-based cermets.The structure,growth and performance characteristics of PVD coatings on the surfaces of TiCN-based cermets,traditional cemented carbides and high-speed steel tool materials were compared to investigate the effects of binder phase composition,substrate surface pretreatment state and deposition temperature on the nucleation and growth,structure and properties of the coating.On this basis,multi-component nano-multilayer coatings was designed and prepared on the TiCN-based cermet tool.The cutting performance,failure mode and mechanism of the coated TiCN-based cermet end mill were explored through milling experiments,which provided some references for the development and application of TiCN-based cermet tools with high wear resistance and long life PVD coating.The main findings are as follows:(1)Growth characteristics of PVD coatings on TiCN-based cermet: Compared with cemented carbide and high-speed steel tool materials,the TiN coating on the TiCN-based cermet has small vertical growth rate,thin coating thickness and weak columnar structure.The growth of the coating is also related to the coating composition.The growth rate of AlTiN coating on Cermet surface is fast and the coating thickness is large.Due to the diffusion effect of atoms,a Ti2 N phase is formed at the contact position between the bottom of Ti transition layer and the cermet substrate,and there is an atomic disorder transition zone with a thickness of about 10 atomic layers between Ti2 N and the Ti C0.7N0.3 phase in the cermet substrate.The Ti transition layer deposited on the cermet is a fine nearly spherical crystal,and the TiN coating grown on the fine spherical crystal is a coarse and fuzzy columnar crystal.The growth mode of TiN coating is the mixed mode of “Volmer-Weber” and “Frank-van der Merwe”.The TiN coatings on these three substrate materials are preferentially oriented with the(111)crystal plane.The TiN coating on the cermet has the greatest degree of preferential orientation.The AlTiN coatings are all preferentially oriented with the(200)crystal plane,and the AlTiN coating on the cermet substrate has the weakest preferred orientation.(2)Performance characteristics of PVD coatings on TiCN-based cermet: Among the three substrate materials,TiN and AlTiN coatings on the cermet have the lowest hardness,and the TiN and AlTiN coatings on the surface of the TiCN cermet have the smallest friction coefficients,and the TiN coating prepared on the TiCN-based cermet by the evaporation method and the AlTiN coating prepared by arc ion plating both show the best wear resistance.The wear mechanism of the coatings on cermet substrate is mainly abrasive wear,accompanied by diffusion wear,oxidation wear and adhesive wear.Due to the differences in thermal expansion coefficient,hardness,lattice type between the coatings and the substrate materials,as well as the effects of residual stress,the bonding strength of the coatings on the cermet is higher than that of the coating on high-speed steel,but slightly lower than that of the coating on cemented carbide.(3)The effect of binder phase composition in TiCN-based cermets on the growth and properties of PVD coatings: the growth rate of AlTiN-based composite coatings is affected by the binder phase composition in the cermets.The higher the phase content is,the faster the coating growth is.Pure Ni binder phase is more favorable for the coating growth than pure Co binder phase.The composite coating on the TiCN-based cermet with high binder phase content has finer grains and higher hardness,but the bonding strength of the coating/substrate couple decreases.(4)The effect of substrate pretreatment on the structure and properties of PVD coatings on the TiCN-based cermet: cermet with mirror polishing has the lowest surface roughness.After pickling,sandblasting and grinding,the surface roughness increases.After the pickling treatment,as the metal bonding phase in the cermet is removed and many pits are formed,the surface roughness of the substrate is the largest.Pickling treatment improves the deposition rate of TiN coatings,but results in the formation of pores at the interface between the coating and the substrate.The residual pores provide favorable conditions for the nucleation of deposited atoms.The coating grains are refined,and the hardness is significantly improved.The deposition rate of AlTiN coating increases with the increase of substrate surface roughness,and the columnar crystal size also increases with the increase of substrate surface roughness.With the increase of the surface roughness of the substrate,the average friction coefficient of the AlTiN coating increases gradually.The grain size of the AlTiN coating on the cermet treated by sandblasting is the smallest.As a result,both the hardness and ratio of hardness to elastic modulus are high,and the wear resistance is the best.(5)The effect of deposition temperature on the growth and properties of PVD coatings on TiCN-based cermet surface: as the substrate deposition temperature increases from 350 °C to500 °C,the vertical growth rate of the AlTiN coating decreases from 2.0 μm/h to 0.9 μm/h.The cross-sectional structure of the coating changes from typical fine columnar crystal to coarse and long block crystal,and then to non-directional equiaxed crystal structure.With the increase of deposition temperature,the hardness and elastic modulus of the coatings decreases,but the ratio of hardness to elastic modulus gradually increases.The AlTiN coating deposited at 350 °C has poor bonding strength,with a bonding force of 24.8N.When the deposition temperature reaches400 °C,the bonding strength of the AlTiN coating is up to 150 N.(6)The structure and performance characteristics of nano-multilayer coating on TiCN-based cermet: compared with the single-layer coating,the surface of nano-multilayer coatings has more large droplets defects.AlTiN/Ti Si N nano-multilayer coating and AlTiN coating were preferentially oriented with(200)plane,while Al Cr N/Ti Si N nano-multilayer coating and Al Cr N coating are preferentially oriented with(111)plane.The AlTiN/Ti Si N nano multilayer coating grew epitaxially on the TiCN core phase in cermets.The TiN phase in the coating formed TiN(220)‖Ti C0.7N0.3(220)and TiN(1 1 1)‖Ti C0.7N0.3(1 1 1)coherent interfaces with a mismatch of less than 1.2% with TiCN core phase in cermets.Due to the strengthening effect of modulus difference and the strengthening effect of alternating stress field,the hardness of nano-multilayer coatings is more than 40 GPa,which is more than 30% higher than that of single-layer coating.Nano-multilayer coatings have the characteristics of low friction coefficient and high hardness.Thus,the wear resistance of nano-multilayer coatings is greatly improved compared with that of single-layer coating.(7)Cutting performance,failure mode and mechanism of the coated TiCN-based cermet end mill: due to the presence of "droplet" defects on the surface of the arc ion plating coating,the cutting force of the coated TiCN-based cermet end mill increases by about 50% and the surface roughness of the workpieces milled from 40 Cr steel with the coated cermet cutter increased compared to the uncoated cermet cutter.Due to the high hardness and wear resistance of the coating,the wear resistance of the coated cermet end mill is better than that of the uncoated.Al Cr N/Ti Si N nano-multilayer coated cermet end mill is suitable for wet and dry milling of 40 Cr steel,and its flank wear width is about 25% and 80% of that of uncoated cermet milling cutter respectively.When the coated cermet end mill is milling 40 Cr steel,normal wear occurs on the flank of the bottom edge.The tip of the cermet milling cutter is seriously broken during wet milling 316 L austenitic stainless steel.During dry milling 316 L austenitic stainless steel,built-up edge is formed on the cutter tip and cutting edge of uncoated cermet milling.AlTiN coating and AlTiN/Ti Si N nano-multilayer coating can effectively eliminate the sticking on the surface of cermet end mill.Due to the high hardness and the ratio of hardness to elastic modulus of the multilayer coating,AlTiN/Ti Si N nano-multilayer coated cermet end mill has the best wear resistance.Tool wear is mainly abrasive wear accompanied by oxidative wear and diffusion wear.