Preparation And Properties Of CrN Based Multi-component Multilayer Erosion Resistant Coating

In aerospace,energy and mechanical engineering,many materials fail due to erosion and wear of solid particles.It is an effective and energy-saving method to prepare anti-erosion protection coatings on precision parts in engineering field by using surface modification technology.Physical vapor deposition（PVD）technology is mainly used for the preparation of thin and dense coatings,which is one of the main technologies for the preparation of erosion resistant coatings due to its characteristics of high bonding strength,low deposition temperature,rich coating materials and multilayer coating.This paper,by using 16 arc source cathode vacuum arc ion plating technology in the preparation of TC11titanium alloy surface coating,firstly optimize the technological parameters of single CrAlN coating,mainly studies the electromagnetic voltage parameters on the coating CrAlN and modulation ratio(L_{Cr/Cr N}:L_Cr/CrAlN)for Cr-Cr N-Cr-CrAlN multivariate the organizational structure of the multilayer coating,the influence of the mechanical properties and erosion resistance.The main results are as follows:CrAlN monolayer coating was prepared by arc ion plating technology,and the influence of key process parameters such as furnace pressure,target current and bias on coating structure,mechanical properties and erosion resistance was optimized by orthogonal test.The results show that the bias voltage has the greatest influence on the structure and performance of CrAlN coating.The lattice orientation of coating growth is closely related to bias pressure,and with the increase of bias pressure,the coating becomes denser and finer.The increase of target current can improve the deposition rate of the coating,but will lead to the increase of large particles on the coating surface,thus reducing the erosion resistance of the coating.Increasing furnace pressure can effectively reduce the size and number of particles on the coating surface,but it can also reduce the deposition rate and hardness to some extent.The optimized process parameters are:target current 90A,bias voltage-100V,furnace pressure 4Pa.A series of CrAlN coatings with different electromagnetic voltages were deposited to optimize the electromagnetic voltage parameters.The experimental results show that the coating deposition rate increases from 0.81μm/h to 1.195μm/h with the change of electromagnetic voltage from 0V to 45V,and the coating grows preferentially along（111）crystal plane.There are large particles and holes in the coating,but the number of particles on the coating first decreases and then increases.When the electromagnetic voltage is 25V,the surface quality of the coating is the best,and the large particles on the coating account for 6.22%of the coating area.With the change of electromagnetic voltage from 0V to 45V,the friction coefficient,wear width and wear rate all show a trend of decreasing first and then increasing,and the electromagnetic voltage of 25V is the best,so the anti-wear ability of the coating is positively correlated with the surface quality of the coating.The wear mechanism between the coating and Si₃N₄ ball is mainly sliding wear.The surface quality and hardness of CrAlN coating directly affect its sand erosion resistance.At 30°and 90°erosion angles,the maximum erosion rate of CrAlN coating samples is only 1/8 and 1/4of that of titanium alloy matrix.The CrAlN coating samples deposited under the electromagnetic voltage of 25V have the minimum erosion rate of 0.43μm/g at 30°,and the erosion rate fluctuates at 1μm/g at 90°.When the erosion Angle is 30°,the erosion mechanism of TC11 matrix is mainly plough or cutting erosion,and the failure mode of CrAlN coating is crack propagation,resulting in brittle flake peeling of coating.When the electromagnetic voltage is 25V,the coating shows the best quality and erosion resistance.The effects of modulation ratio(L_Cr/CrN:L_Cr/CrAlN)on the microstructure,mechanical properties and erosion resistance of Cr-Cr N-Cr-CrAlN multilayer coatings were studied.The surface cleanliness of Cr-Cr N-Cr-CrAlN multi-layer coating is much better than that of single-layer coating,and its erosion resistance is also improved.As the ratio of L_{Cr/Cr N}:L_Cr/CrAlN continues to decrease,the number and size of particles on the coating decrease first and then increase,which is the smallest when L_{Cr/Cr N}:L_Cr/CrAlN=1:2,and the value is about 2.23%.The hardness and binding force of Cr-Cr N-Cr-CrAlN multi-layered coatings are on the rise.When the erosion Angle is 90°,the erosion rate of TC11 substrate is more than 5 times that of coating.Among the coatings with different modulation ratio,the Cr-Cr N-Cr-CrAlN coating with the modulation ratio of 1:2 had the lowest erosion rate,with a value of 0.78μm/g.In the process of erosion,nitride layer hardness is high,prone to brittle fracture,metal layer hardness is low,can absorb part of the erosion energy,will prevent the coating to continue to fracture.At the same time,reducing the number and size of large particles on the coating can improve the erosion resistance of the coating.When the erosion Angle is 30°,the erosion rate of TC11 substrate is 6 times that of coating.The erosion rate of coatings with different modulation ratios is basically the same,with a value of about 0.4μm/g.The failure mode of coating is still brittle chip peeling caused by crack quality and erosion resistance.