Study On Microstructure And Properties Of Laser Cladding CoCrFeNiW_x High Entropy Alloy Coating On Tungsten Heavy Alloy

Tungsten heavy alloy is a dual phase composite material prepared by powder metallurgy process using tungsten as the matrix and adding a small number of alloying elements such as Co,Fe,Ni,etc.With high strength,low coefficient of thermal expansion,and good thermal conductivity,it is one of the ideal materials for aluminum alloy die casting molds.During the production process,tungsten heavy alloy die casting molds undergo various forms of failure,such as thermal fatigue and thermal wear,due to the impact of high-temperature liquid metal and the cyclic quenching and heating effects.High entropy alloy has advantages such as high hardness,high wear resistance,and high thermal stability,and is currently used in many engineering fields such as aerospace,automobile and ship manufacturing.In this study,CoCrFeNiW_x（x=0,0.2,0.4,0.6,0.8,1）high entropy alloy coatings were prepared on the surface of a tungsten heavy alloy die casting mold using laser cladding process.The phase structure and microstructure of the coating were analyzed using X-ray diffraction,scanning electron microscopy,and other testing methods.The microhardness,wear resistance,and tempering stability of the tungsten heavy alloy substrate and high entropy alloy coating were tested.The effects of process parameters and W element content in the high entropy alloy on the microstructure and properties of the coating were studied.The effect of laser cladding process parameters on the microstructure and properties of CoCrFeNiW high entropy alloy coating was experimentally studied.The results show that with the increase of laser power,the content of W in columnar dendritic and interdendritic structures of the coating increases,and the average hardness and relative wear resistance of the high entropy alloy coating gradually increase.As the scanning speed increases,the microstructure of the high entropy alloy coating is refined,the content of W element in the columnar dendritic and interdendritic structures decreases,and the average hardness and relative wear resistance of the high entropy alloy coating gradually decrease.When the laser power is in the range of1400W to 1600W and the scanning speed is in the range of 360mm/min to 480mm/min,the coating surface is flat and smooth,with good forming quality and no obvious defects.The effect of W content on the microstructure and properties of CoCrFeNiW_x high entropy alloy coatings was experimentally studied.The results show that the CoCrFeNiW_x high entropy alloy coatings prepared by laser cladding on the surface of tungsten heavy alloy have a good metallurgical bonding with the substrate.The phase structure of the coating is composed of FCC solid solution phase,W elemental phase,andμphase.With the increase of W content,the atomic percentage of W element inμphase of the coating increases,and the morphology ofμphase changes.As the W content increases,the average hardness of CoCrFeNiW_x high entropy alloy coating gradually increases.When the W content x=1,the average hardness of the coating is the highest,reaching 506.5HV_0.5,which is 1.45 times that of the tungsten heavy alloy substrate.With the increase of W content,the wear resistance of the CoCrFeNiW_x high entropy alloy coating first increases and then decreases.When the W content x=0.8,the average friction coefficient and wear amount of the high entropy alloy coating are the lowest,the wear surface of the coating is relatively flat and smooth,with fewer pits,and its relative wear resistance is2.41 times that of the tungsten heavy alloy substrate.The tempering stability of tungsten heavy alloy matrix and CoCrFeNiW_0.8 high entropy alloy coating was experimentally studied.After tempering at 400℃for 12 hours,the microstructure and its morphology of the high entropy alloy coating did not change significantly.The average hardness of the high entropy alloy coating is 466.5HV_0.5,which is 1.47 times that of the tungsten heavy alloy substrate.The depth of abrasion marks and furrows on the worn surface of the coating is relatively shallow,and its relative wear resistance is 2.35 times that of the tungsten heavy alloy substrate.