Surface Repair For Copper Based Parts By Laser Cladding And Enhanced With CoCrCuFeNiMo High Entropy Alloy Coating

Copper and copper alloys have excellent seawater corrosion resistance and marine biological corrosion resistance,and are widely used in key parts of marine engineering.However,due to its low strength and poor wear resistance,the surface of the parts often fails due to wear and cavitation,which affects the service performance and service life of copper alloy parts.Therefore,the failure repair on the surface of copper based parts is of great significance for extending the service life of copper-based parts and reducing waste of resources.However,there are special difficulties in the surface repair process of copper-based parts.First,due to the high infrared laser reflectivity of copper,the laser energy absorption rate in the laser cladding of copper composite powder is low,and the cladding process cannot be completed normally.Secondly,the corrosion resistance of the coating prepared by copper composite powder cladding is obviously lower than the surface corrosion resistance of copper based prototype parts due to the existence of intergranular corrosion and pinhole corrosion.Therefore,aiming at the problems of high reflectivity of copper powder to infrared laser and low absorption rate of laser energy,this paper proposes to improve the high energy absorption rate of laser and low laser reflectivity by surface modification of copper powder with C and Al₂O₃,and to repair the geometric dimensions of the failed part surface by laser cladding of copper composite powder.In order to solve the surface corrosion resistance of laser cladding copper composite powder coating,this paper proposes to cladding a layer of high entropy alloy coating on the basis of dimensional repair coating.The high entropy alloy coating on the surface has a unique design concept and excellent comprehensive performance to ensure good mechanical properties and corrosion resistance while repairing the surface.The main research work of this paper is as follows:（1）In order to solve the problem of high infrared laser reflectivity of metal powder（copper powder）and improve the laser absorption rate of high reflectivity powder,a composite powder preparation method combining sol-gel and heat treatment was proposed to modify the surface of copper powder.By optimizing the heat treatment temperature and time,the copper composite powder with less difference in particle size and sphericity compared with the original powder was obtained.Through experimental research and analysis of the influence of laser cladding process parameters on the forming quality and mechanical properties of copper composite coating,a set of appropriate laser cladding process parameters of copper composite powder coating were obtained,and the laser cladding process of copper composite powder on the surface of copper based parts was realized.（2）The particularity of laser cladding copper based coatings on copper based parts is studied.The corrosion resistance of the coating prepared by laser cladding of copper composite powder after surface modification of copper powder decreased significantly.By analyzing the electrochemical polarization characteristic curve and combining with the metallographic structure of the coating,it is clear that the copper composite powder cladding coating has intergranular and small hole corrosion problems,and a solution to further improve the laser cladding surface repair is proposed.In order to solve the problem of poor corrosion resistance of laser cladding coating with copper composite powder,a high entropy alloy coating was proposed based on laser cladding copper base coating.（3）Through the calculation of phase structure determination parameters such as mixing entropy,mixing enthalpy and atomic radius difference of high entropy alloy system,the composition of Co Cr Fe Ni Mo high entropy alloy coating suitable for copper based surface was designed.The multi-factor experiment was arranged by using the orthogonal table,and the coating dilution rate and contact angle were optimized by combining the analysis method of Taguchi and TOPSIS method.The coating is mainly composed of FCC phase andμphase,which is mainly dendritic structure,and a good metallurgical bond is formed between the coating and the substrate.The average microhardness of the coating is 645HV_0.2,the wear volume is0.0013mm³and the self-corrosion current density is 4.094×10^-7A·cm^-2.The microhardness,wear resistance and corrosion resistance of the coating are better than those of the substrate.（4）In order to investigate the effect of copper segregation to the coating in copper based parts on the coating performance,different contents of Cu were actively added to study the effect of Cu content on the structure and performance of Co Cr Cu_xFe Ni Mo（x=0,0.3,0.5,0.7,1.0,1.3）high entropy alloy coating.The results show that when x≤0.7,the coating is dominated by FCC phase andμphase;when x=1.0 and 1.3,the coating is dominated by FCC phase,BCC phase andμphase.Theμphase can effectively hinder the micro-cutting and micro-shearing of the coating by the asperities of the friction pair.The corrosion resistance of Cu0～Cu1.3 coating in3.5%Na Cl solution is complex.The corrosion resistance of coatings from high to low is:Cu0.7,Cu0.3,Cu1.3,Cu0.5,Cu0,Cu1.0.The results show that a small amount of Cu segregation has little effect on the comprehensive properties of the coating.（5）In order to improve the research on the surface strengthening of high entropy alloy coating on metal parts,this paper proposes to further analyze the phase regulation and performance influence of Co Cr Cu_0.3Fe Ni Mo_x（x=0,0.3,0.5,0.8,1.0）high entropy alloy coating by changing the Mo content.The results show that the Mo0 coating is mainly FCC phase;Mo0.3～Mo1.0 coatings increase the BCC phase andμphase.When excessive Mo element was added,the BCC phase in the coating gradually decreased,and theμphase was formed as the main phase to adjust the coating properties.And the average microhardness and wear resistance of the coating were improved.Theμgenerated in the coating has a positive effect on improving the microhardness and wear resistance of the coating.With the increase of Mo content,the corrosion resistance of Mo0～Mo1.0 coatings from high to low is:Mo1.0 coating,Mo0.3 coating,Mo0.5 coating,Mo0.8 coating,Mo0 coating.The potential of BCC phase andμphase in the dendritic structure is higher.The results show that the comprehensive mechanical properties and corrosion resistance of the coating can be obviously regulated by changing the Mo content,can be applied to the surface strengthening.