Study On Processing And Properties Of High Entropy Composite Coatings Prepared By Laser Cladding

AlCoCrFeNi HEA coatings with good comprehensive properties were prepared by laser cladding technique.The mechanical properties of the composite coating were improved by adding 15wt.%WC hard particles and 20wt.%WS2 to the HEA coating.First,a two-factor five-level test was conducted on the laser scanning power(power range:150W-350W,gradient:50W)and laser scanning rate(scanning rate range:120mm/min-360min/min,gradient:60mm/min)during the test.The forming quality of coatings were analyzed to choose the optimal parameter set in the whole factor experiment.Then,single factor experiment was adopted to thoroughly explore the effect of two factors,laser power P and laser scanning speed V,on the comprehensive properties of high entropy alloys coating.XRD,EDS,SEM and other analytical methods were utilized to analyze the phase composition,crystal structure,chemical components and microstructure of coatings.The microhardness tester and the friction wear tester were used to detect the microhardness,friction performance and fracture toughness of coatings.Then,the coatings were immersed in the 3.5wt.%NaCl solution for corrosion resistance experiments.(1)The coating forming quality(surface roughness,surface roughness,cross section,microstructure,hardness)of all the two-factor five-level test samples were analyzed.According to the analysis results,the coating with good surface forming quality and high hardness can be prepared within a reasonable range of laser scanning power and laser scanning rate.When the laser scanning rate is 240mm/min,the coating quality of different laser power is better,and when the laser power is 200W,the coating quality of different laser scan rate is better.These two sets of parameters were selected for single factor test.(2)Selecting laser scanning rate of 240mm/min,through a single-factor test to analyze the impact of different laser scanning power on coating performance.It can be seen from the test analysis,the coatings were mainly composed of BCC and FCC phase.When the laser scanning power is large,the diffraction peak strength of FCC phase in the coating exceeds the BCC phase diffraction peak.The diffraction peak of WC is not present in XRD analysis,and the diffraction peak of WS2 is weak,but the diffraction peak of Cr7C3 and(Cr,Fe,W)C appears.Changing the laser scanning power leads to significant changes in the microhardness,frictional wear,corrosion resistance,and fracture toughness of the coating:as the laser scan power increases,the microhardness of the coating increases and then decreases,with a smaller fluctuation in the 150W-300W range of 981HV0.1-1143HV0.1,when the power reaches 350W,the coating microhardness decreases significantly;When the laser power is in the range of 150W-250W,the fluctuation of friction coefficient is small and the value is between 0.43-0.51.At the same time,the ranges of grinding width and depth are 392?m-472?m,12?m-14?m,respectively.When the power exceeds 300W,The coefficient of friction,grinding width and depth rise significantly,the coefficient of friction is about 0.62-0.73,the grinding width and depth are 503?m-652?m,15?m-18?m.The wear form of the coating belongs to the abrasive wear.As the laser power increases,the self-corrosion current density of the coating decreases and then increases(150W-300W),the minimum corrosion current is 1.5764E-6A/cm2,when the laser scan power reaches 350W,the self-corrosion current density decreases,at which time the coating porosity decreases,the thickness is largest,the thickness is about 200?m;The fracture toughness of the coating decreases first and then rises as the laser power increases.When the laser power is 350W,the fracture toughness of the coating is the largest at 14.72Mpa·m1/2.(3)The laser power was selected to be 200W,and the influence of different laser scanning rates on the coating performance was analyzed through single-factor test.From the experimental analysis,the phase composition in the coating is similar to the laser scanning rate group.But the laser scanning rate is changed,the diffraction peak of the BCC phase in the coating is substantially higher than that of the FCC phase.With the increase of the laser scanning rate,the microhardness of the coating increases first and then decreases.The fluctuation range is small,it is about 998HV0.1-1143HV0.1;The friction coefficient,wear scar width and depth of the coating first decrease and then rise,the friction coefficient is about 0.43-0.53,the wear scar width and depth are 392?m-453?m,12?m-15?m,The wear method belongs to abrasive wear;The self-corrosion current density of the coating first decreases and then increases,the minimum corrosion current is 1.5764E-6A/cm2;The fracture toughness of the coating gradually decreases,the maximum value is 9.91 Mpa·cm1/2.