MoFe_xCrTiWAlNb_y Refractory High-entropy Alloy Coating Fabricated By Laser Cladding

In order to obtain the coating materials with high performance tool steel coating.The square spot and round spot laser cladding tests were used to prepare the high entropy alloy?HEA?coating on M2 tool steel?W6Mo5Cr4V2?.The differences of the structure and properties between the two processes were compared and analyzed.The effects of Fe and Nb on the structure and properties of the coating were studied;The effect of annealing temperature on the microstructure and properties of high melting point and high entropy alloy coating was investigated.SEM,XRD and EDS were used to analyze the morphology,composition and phase structure of the two coatings.The coating properties were tested by microhardness tester and friction and wear tester.The main conclusions are as follows:?1?After ball milling for 4 hours,no alloying took place,but deformation took place.The alloy powder was finer and more uniform,with an average diameter of56.1?m.The main phase structure of HEA coating prepared by laser cladding with circular spot is BCC and MC carbide,while the main phase structure of HEA coating prepared by laser cladding with rectangular spot is BCC,hcp-Fe₂Nb and MC carbide.There is obvious phase separation phenomenon in the coating with round spot,while the laser cladding layer with square spot has shallow melting depth,small dilution ratio,and the microstructure is mainly composed of irregular dendrite and granular carbide.The average hardness of laser cladding coating with square spot is about850HV,and that of laser cladding coating with circular spot is about 680HV.Compared with the HEA coating prepared by the circular spot,the HEA coating prepared by the square spot has low friction coefficient,small wear amount and smooth wear surface.The main wear mechanism is abrasive wear.?2?At the same time,adjusting the content of Fe and Nb elements,the coating is mainly composed of BCC,MC and Laves phases,and no new phase is produced;the microstructure of mofexcrtiwanby high entropy alloy coating is mainly composed of gray matrix,white dendrite,dark gray irregular particles and feather like and radiation like eutectic structure.When the ratio of Fe and Nb element content is greater than 1,the coating is mainly composed of white dendrite,gray matrix,dark gray irregular particles and a small amount of black circular particles wrapped inside.At this time,the average hardness of the coating is low,the wear performance is poor,and the wear amount is high.When the ratio of Fe and Nb element content is about 1,the coating forms a eutectic group composed of matrix and feather and radial alternately There are dark gray irregular particles and a small amount of black round particles on the fabric.Among them,the eutectic structure of Fe_2.5Nb_2.5coating has the smallest lamellar spacing and the densest morphology.The hardness of the coating increases with the content of Fe and Nb elements,and the wear resistance is the best.When the ratio of Fe to NB is less than 1,the main structure of the coating remains unchanged,but only a small amount of eutectic structure exists.?3?At 500?,550?,600?and 700?,the heat preservation annealing experiments of Mo Fe_2.5Cr Ti WAl Nb_2.5high entropy alloy coating were carried out for4H.The results show that the main phases of the coating after heat treatment are consistent with the cladding state.With the increase of annealing temperature,the hardness of the coating increases first and then decreases.The microhardness of the coating is higher than that of the substrate and the cladding state,which shows that the high melting point and high entropy alloy coating of Mo Fe_2.5Cr Ti WAl Nb_2.5has good high temperature softening resistance.