| In order to meet to the development of modern cutting technology,this research work focuses on optimizing high temperature oxidation resistance,friction performance,thermal stability and cutting performance of high aluminum content AlTiN coating.In this paper,introducing of multi-alloying,nanocomposite structure and nanomultilayer structure was used to improve service performance of the AlTiN coating.First,the effects of adding active element Y on the mechanical,anti-oxidation and high-temperature friction properties of the AlTiN coatings were investigated.Second,the nano-composite structure?i.e.,a-Si3N4 interfacial phase-coated coating?was applied to improve the oxidation resistance of the coating.The cutting performance was discussed as well.Third,the effects of varying modulation period on interfacial structure,thermal stability,lifetime and failure mechanism of AlTiN/AlTiSiYN nanomultilayer coatings were investigated.The main results of this paper were summarized as follow s.1)After the doping of active element Y into the AlTiN,it favors the formation a solid solution-type AlTiYN coating.The average grain sizes of the coating were refined and the microstructure become dense after the Y introducing.In addition,hardness,toughness and adhesion strength were improved.The XRD phase analysis showed that the Y element was dissolved into the AlTiN lattice.The XRD characteristic diffraction peaks of the AlTiN and AlTiYN coatings shifted to low angles.The addition of 0.76 at.%Y enhances the high-temperature oxidation resistance of the AlTiN coating significantly.The active element Y addition produces anti-wear and frication reduction effects.The wear rate of the AlTiYN coating was lower than that of the AlTiN at 800°C900°C.The friction coefficient of the AlTiYN coating decreases from 0.45 for 800°C to 0.35 for900°C.2)Adding SiNx interface phase prefers to reduce the solubility of Al in the AlTiN,resulting in the precipitation of h-AlN and hardness decrease.However,the increase of plastic deformation resistance and adhesion strength can be achieved.XRD phase analysis showed that the AlTiSiN and AlTiSiYN indicate the phase of solid solution-type?Al,Ti?N,h-AlN and c-TiN.The AlTiSiN and AlTiSiYN coatings illustrated a high oxidation resistance than that of the AlTiN.The Si element promotes the diffusion of Al during the oxidation.The surface layer preferentially forms a protective and dense oxide layer.The Y element possesses high activity which makes it prefers to reacte with oxidation.The formation of Y2O3 at the grain boundary hinders the inward diffusion of oxygen,thereby improving the high temperature oxidation resistance of the coating.The oxidation onset temperatures of the AlTiSiN and AlTiSiYN reach1080°C and1100°C,respectively.In addition,the AlTiSiYN coating shows excellent adhesion strength,high temperature oxidation resistance and thermal stability,resulting in a larger lifetime compared to those of the AlTiN and AlTiYN coating tools.3)Nanomultilayer AlTiN/AlTiSiYN coatings with modulation periods of?=20.9,13.6,6.2 nm show dense structure and refined grains.The AlTiN/AlTiSiYN coating with the modulation period of 13.6 nm exhibit the largest hardness 23.5±0.5GPa.The introduction of multilayer structure promotes the amplitude modulation decomposition of AlTiN coating and inhibits the formation of w-AlN,thereby expanding the age hardening temperature range and improving the high temperature thermal stability of the coating.In the turning experiment,the lifetime of those AlTiN/AlTiSiYN coating tools are nearly the same.However,the lifetime of the nanomultilayers is much higher than those of the multicomponent AlTiYN and nanocomposite AlTiSiN monolayer coatings.In addition,the primary failure mechanisms behind the turning of the AlTiN/AlTiSiYN nanomultilayer tools are adhesion and oxidation wear. |
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