| The microstructure characteristics of materials are closely related to their properties.Starting from the microstructure characteristics of coatings,three kinds of Ti-Al-Si-N coatings with common structure characteristics are summarized and found that the gradient coating can effectively reduce the internal stress of coatings,improve the toughness,hardness and wear resistance of coatings,and play an extremely important role in improving the life of coated tools and coated dies.In this paper,a new type of Ti-Al-Si-N multi-layer gradient coating structure is designed based on the structure of nano multilayer coating and nano composite coating and the non-uniform distribution gradient structure(Ti N/Ti Al N/Ti Al Si N/Ti Si N).A series of Ti-Al-Si-N multilayer gradient coatings were prepared by cathodic arc ion plating.The microstructure,physical and mechanical properties,friction and wear properties of Ti-Al-Si-N multilayer gradient coatings were systematically studied.The specific research work and conclusions are as follows:(1)The bonding strength of Ti-Al-Si-N multilayer gradient coating and the design of layer structure.Based on PVD coating design criteria,Ti-Al-Si-N multilayer gradient coating was designed and prepared with gradual transition of properties in the layer region(Ti N,Ti Al N,Ti Al Si N,Ti Si N,etc.).The film substrate bonding force of the coating and the rationality of the structure design of each layer area of Ti-Al-Si-N multilayer gradient coating were analyzed from the angle of energy,residual thermal stress and direct deposition of Ti Al Si N layer on the substrate.The element diffusion interface is formed between Ti-Al-Si-N multilayer gradient coating and coating substrate,and the interface bonding mechanism is chemical bonding.The thickness of each layer is 41.7nm,1508.3nm,950nm and 500nm respectively,and they have excellent physical matching performance and chemical compatibility with each other.The bonding force of Ti-Al-Si-N multilayer gradient coating was HF1 by indentation method and the residual thermal stress was 427.27Mpa.(2)Characterization of cross section microstructure and mechanical properties of Ti-Al-Si-N multilayer gradient coating.The microstructure of Ti-Al-Si-N multilayer gradient coating was observed by TEM.In the large magnification observation of Ti Al N layer region,it is found that there are two kinds of special coating microstructure characteristics,Ti Al N/Ti N nano multilayer coating structure and nc-(Ti,Al)N/?-Si3N4 microstructure.In the former,the thickness of Ti N and Ti Al N modulation layer is 1 nm and 0.5 nm respectively,while in the latter,the thickness of amorphous layer and the size of nanocrystals are about 2?3 nm and 6 nm respectively;The structural design of the coating is optimized according to the observation results,and the correctness of the thickness of each layer is verified.The hardness and elastic modulus of Ti-Al-Si-N multilayer gradient coating are 27.7Gpa and 338.0Gpa,respectively.The hardening mechanism of Ti-Al-Si-N multi-layer gradient coating is analyzed by using the theory of modulus difference,alternating stress field and S.veprek's nc-Ti N/?-Si3N4 model.Finally,the strengthening mechanism of Ti-Al-Si-N multilayer gradient coating is determined as S.veprek's nc-Ti N/?-Si3N4 model.(3)Surface microstructure characterization and friction and wear properties of Ti-Al-Si-N multilayer gradient coating.The results show that there are some white solid particles,pinholes and pits on the surface of Ti-Al-Si-N multilayer gradient coating,and the grain size of the coating is 13?15nm;The friction coefficients of Ti-Al-Si-N multilayer gradient coating with Al2O3 ceramic ball and Cr15 steel ball are 0.54 and 0.82 respectively,and the causes of friction coefficient variation caused by different friction pairs are analyzed;The wear depth,width,volume and wear rate of Ti-Al-Si-N multi-layer gradient coating are calculated,which are0.59?m,9.06?m,2.82?m3 and 7.06x103?m3/(n·m),respectively.The wear mechanism of Ti-Al-Si-N multilayer gradient coating in each friction and wear stage is analyzed,and it is determined that the wear mechanism of Ti-Al-Si-N multilayer gradient coating is the synergistic effect of slight abrasive wear,abrasive wear and slight adhesive wear. |
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