| The surface coating can effectively reduce the tool wear during machining,resulting in improved processing efficiency and quality,and thus has become a research focus in the field of metal cutting.As a typical tool coating,AlTiN possesses high hardness and excellent thermal stability,which has been successfully applied in the industry.However,the endless pursuit of production efficiency and the extensive application of difficult-to-machine materials have placed increasing demands on cutting tools and above surface coatings.The tool coating not only needs to have high hardness and wear resistance but also has superior adhesion strength and high-temperature stability.Production technology and materials are the two critical factors that promote the upgrading of manufacturing.The PVD preparation technology of tool coatings includes arc ion plating and magnetron sputtering,each of which has advantages and complements each other.In terms of material design,the compositionally modulated nano-multilayer structure can combine the features of different constituents and synergistically improve the hardness and toughness,which attracts widespread attention for hard nitride coatings in recent years.Starting from the design of nano-multilayer structure,this paper systematically studied the structure and high-temperature properties of AlTiN/AlCrSiN coating.Then based on the development of arc ion plating/magnetron sputtering hybrid deposition technique,high adhesion strength,and low residue stress AlTiN-based nano-multilayer coatings were synthesized and investigated concerning high-temperature tribological properties,oxidation resistance,and high-speed dry cutting performance.The main research results obtained are as follows:1)The AlTiN/AlCrSiN nano-multilayer coatings with various modulation periods were prepared by arc ion plating.The study found that when the modulation period is 8.3 nm,the AlTiN/AlCrSiN coating exhibits the best mechanical properties.In addition,the AlTiN/AlCrSiN coating only forms an oxide layer of-0.3 after oxidation at 1000?.High-temperature ball-on-disc tests show that the AlTiN/AlCrSiN multilayer with a period of 8.3 nm has better wear resistance than single-layer coatings.Moreover,the lifetime of AlTiN/AlCrSiN(?=8.3 nm)coated tools during high-speed turning SKD11 die steel is?4.5 times that of single-layer AlTiN coated tools.2)The process parameters of arc/sputtering hybrid deposition,such as total pressure,nitrogen partial pressure,sputtering power,etc.,have a significant impact on the structure and properties of AlTiN coatings.The hybrid AlTiN coatings obtain a nano-multilayered structure,formed by periodically stacking arc-evaporated layers and sputtered layers.When the modulation period is 9.0 nm and the modulation ratio of arc-evaporated to sputtered layer is 3:1,the sputtered AlTiN layer epitaxially grows on the arc-evaporated AlTiN layer,and this hybrid coating achieves the highest hardness(>33 GPa)and good toughness and adhesion strength.The hybrid AlTiN coating shows better wear resistance than single arc or sputter deposited AlTiN at room and high temperatures.3)Epitaxially grown arc/sputtering hybrid AlTiN/AlCrN coatings exhibit a single-phase face-centered cubic structure with fine columnar grain morphologies.Hybrid AlTiN/AlCrN coating with ?=9.3 nm has the highest hardness,elastic modulus,H/E*,and adhesion strength owing to the combined action of the shear modulus difference model,Hall-Patch effect,and alternating stress field theory.During the elevated temperature oxidation tests,the dense protective mixed(Al,Cr)oxide scale on the surface of the multilayer coating results in a prominently improved oxidation resistance.Besides,refined grain size,reduced density of internal pore,and a significant amount of coherent interfaces as diffusion barriers are also beneficial to the oxidation resistance of hybrid AlTiN/AlCrN coating,which results in an improved wear behavior both at room temperature and 600?.4)The high-speed cutting performance of the hybrid AlTiN coatings(namely H-AlTiN)was further investigated and compared with the commercial AlTiN coating(namely B-AlTiN).In high-speed dry cutting of 316L stainless steel,the flank wear width of B-AlTiN coated tools is 1.7 times that of H-AlTiN coated tool after the same cutting distance.The primary wear forms of the B-AlTiN coating are groove wear of the cutting edge and the rake and flank wear caused by adhesive,abrasive,oxidative,and diffusion wear.While the H-AlTiN coated tool reveals slight wear in the cutting edge and adhesive,abrasive,oxidative,and diffusion wear can also be seen in the rake and flank faces of H-AlTiN.When turning QT600-3 nodular cast iron,the wear mechanism of B-AlTiN coated tools is the thermal fatigue and abrasive,oxidative,adhesive,and diffusion in the rake and flank faces.The wear of rake and flank faces of H-AlTiN coated tool resulted from abrasion,adhesion,oxidation,and diffusion.Consequently,H-AlTiN coating has higher hardness,adhesion strength,and toughness.Therefore,it exhibits better wear resistance than B-AlTiN coated tools in high-speed dry cutting.The main wear mechanisms of B-AlTiN coated tools in high-speed dry cutting of 316L stainless steel are notch wear of the cutting edge as well as the front and flank wear caused by abrasive,oxidation,and diffusion wear;the main wear mechanism of H-AlTiN coated tools is slight peeling off of coating at the cutting edge,front and flank wear caused by abrasive,oxidation and diffusion wear.When the workpiece material is QT600-3 nodular cast iron,the main wear mechanisms of B-AlTiN coated tools in high-speed dry turning are thermal fatigue crack propagation,abrasive,oxidative,adhesive,and diffusion wear on the front and flank surfaces;the main wear mechanisms of H-AlTiN tools are front and flank wear caused by abrasive,oxidative,adhesive,and diffusion wear.The improved mechanical properties of hybrid AlTiN coating give rise to a better cutting performance than B-AlTiN coated tools in high-speed dry cutting of 316L stainless steel and QT600-3 nodular cast iron. |
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