Research On Laser Cladding Of BCC-based Eutectic High-entropy Alloy Coatings

Eutectic high-entropy alloys can simultaneously possess high strength and high ductility,which have potential applications in industrial fields.In order to obtain refractory eutectic high entropy alloys(REHEAs)coating with both strength and toughness,a series of AlFeCrMoNb_x high entropy alloy coating was fabricated by laser cladding on M2 high-speed steel.The effects of laser processing parameters and Nb content on the microstructure and properties of the coatings were systematically studied by OM,SEM,XRD,micro-hardness tester and wear tester,and the evolution law of the microstructure and properties of the coating after annealing at 750?-1050?for 8 h was explored.The following conclusions were obtained:(1)When v=3 mm/s,with the increase of laser power(P=1600 W-2000 W),the microstructure of coating changes from hypereutectic to hypoeutectic,and the hardness and wear resistance of the coating decrease.When P=1800 W,with the increase of scanning speed(v=3-5 mm/s),the microstructure of coating changes from hypoeutectic to hypereutectic,and the hardness and wear resistance of the coating increase.(2)For AlFeCrMoNb_x(x=0.4,0.6,0.8,1)coatings at P=1800 W and v=5mm/s,the coating with x=0.4 is a single-phase BCC solid solution.When x=0.6,the microstructure of the coating consists of preeutectic BCC solid solution,(BCC+Laves)eutectic and Nb C carbide.With the increase of Nb content,the microstructure of coating transitions from hypoeutectic to hypereutectic.For AlFeCrMoNb_x(x=1,1.2,1.4,1.6,1.8,2)coatings,when P=1800 W and v=3 mm/s,the microstructure of coating changes from hypoeutectic to hypereutectic as the Nb content increases;at x=1.8,the(BCC+Laves)eutectic with lamellar structure is obtained,and the microhardness and volume loss of coating are 702 HV_0.2and 0.16 mm³,respectively.(3)After annealing at 750?,the microstructure,hardness,and wear resistance of AlFeCrMoNb_1.8 eutectic high entropy alloy coating are similar to those of as-cladded coating,which indicates that it has good softening resistance at high temperature.After annealing temperature exceeds 850?,the volume fraction of precipitated phases gradually increases with the increase of temperature,but their size gradually increases with the increase of temperature,and the eutectic lamellar spacing gradually widens,which will lead to the weakening of solution strengthening,dispersion strengthening and fine grain strengthening effects of the coating,and reduce its hardness and wear resistance.