| Ternary boride Mo2FeB2 cermets have high melting point,high hardness,excellent high temperature stability and corrosion resistance,and are widely used in automobile,energy,equipment manufacturing,mold manufacturing and other fields.It is the research focus of ternary boride cermets.At present,Mo2FeB2 cermets are prepared by vacuum sintering process,which is characterized by large equipment investment,low production efficiency,high cost and poor adaptability in engineering application.The study of Mo2FeB2 cermet micropowder and its laser cladding technology is of great significance for the intelligent,low-cost,personalized,small batch production of wear-resistant,corrosion-resistant products.In this paper,Mo2FeB2 cermet powder for laser cladding was prepared by induction melting gas atomization method.By means of scanning electron microscopy(SEM),X-ray diffractometer(XRD),electron probe,hardness tester and wear test,the effects of RE(rare earth)and TiC contents in powder and laser cladding process parameters on the microstructure and properties of the cladding metal were studied.The thermal process of laser cladding was simulated by Ansys software.The test results show that the powder is spherical,and there are satellite balls and slight coating phenomenon on the surface.Particle size normal distribution;The powders with diameters of 74 μm(200 mesh)and 105 μm(140 mesh)showed well-developed equiaaxial crystal petals.With the decrease of particle size,the fluidity becomes worse,but the loose packing density does not change much.The powder is mainly composed of Mo2FeB2 phase with square crystal structure and binary borides CrB,MoB,Fe2B phase.Compared with the powder without rare earth,the hard phase of Mo2FeB2 cladding layer with 2%rare earth powder is obviously refined,and the hard phase is mainly massive.When the amount of rare earth is increased to 4%,the hard phase begins to connect and grow.When the amount of rare earth is increased to 8%,the hard phase is coarse and uneven.The hardness of 0%,2%,4%and 8%rare earth powder cladding layer is 627 HV,923 HV,1008 HV and 742 HV,respectively.When 5%,10%and 15%TiC were added,the hard phase of cladding layer changed from strip to block,and the size of hard phase decreased with the increase of TiC content.The average microhardness of 0%,5%,10%and 15%TiC powder cladding coating is 627 HV,994 HV,962 HV and 656 HV,respectively,and the highest hardness is obtained when 5%TiC is added.The microhardness of 2%Rare-earth+5%TiC powder cladding layer is 1020.4 HV,which is improved to a certain extent compared with that of the coating alone.With the increase of scanning speed from 300 mm/min to 450 mm/min,the hard phase of the cladding layer containing 2%rare earth powder R gradually changes from thin strip+a few blocks to fine blocks.The microhardness of 300 mm/min,350 mm/min,400 mm/min and 450 mm/min cladding layers are 798.15 HV,717.87 HV,923.47 HV and 992.29 HV,respectively.Wear weight loss was 16.7 mg,15.2 mg,12.7 mg and 17.8 mg,respectively.lncreasing the scanning speed has a tendency to increase the microhardness of the cladding layer,the cladding metal is mainly adhesive wear,and the scanning speed of 400 mm/min has the best wear resistance.At the scanning speed of 400 mm/min,350 mm/min and 300 mm/min,the Mo/Fe values of the hard phase of the cladding layer containing 2%rare earth+5%TiC powder RT are 1.55,1.20 and 1.32,respectively,which are all less than 2,indicating that Cr element replaces Mo element in Mo2FeB2 lattice.The area fraction of hard phase is 35.00%,25.32%and 23.54%,and the area fraction of scanning speed 400 mm/min is the largest.The microhardness of cladding layer is 1020.7 HV,903.1 HV and 908.3 HV,respectively.Under the laser power of 3500 W,4000 W,4500 W and 5000 W,the hard phase area fraction of R powder cladding layer is 60.31%,54.74%,50.07%and 40.60%,respectively.With the increase of laser power,the hard phase area fraction of R powder cladding layer decreases gradually.The micro-vickers hardness of the cladding layers are 856.2 HV,923.5 HV,1033.3 HV and 642.6 HV,respectively.The hard phase of RT powder cladding layer with laser power of 3500 W is long strip,the hard phase of RT powder cladding layer with laser power of 4000 W is short axis and block,and the hard phase of RT powder cladding layer with laser power of 4500 W and 5000 W is basically block,but the hard phase of 5000 W decreases obviously.The hard phase area fraction of cladding layer with laser power of 3500 W,4000 W,4500 W and 5000 W is 32.82%,35.00%,32.93%and 10.70%respectively.When laser power increases to 5000 W,the hard phase area fraction of cladding layer decreases greatly.The micro-vickers hardness of the cladding layer are 970.7 HV,1020.7 HV,1013.8 HV and 982.3 HV,respectively.The finite element model of laser cladding heat process was established to verify the reliability of rectangular spot heat source model.The phase transformation process of molten pool was analyzed by using gibbs free energy of molten pool metallurgical reaction.The results show that the laser power is 3500 W,4000 W,4500 W and 5000 W,and the generation time of Mo2FeB2 in molten pool is 0.8 s,1.6 s,2.2 s and 3.5 s,respectively.The generation time of Mo2FeB2 in 300 mm/min,350 mm/min,400 mm/min and 450 mm/min molten pool is 3.6 s,2.4 s,1.7 s and 1 s respectively,and the dilution rate is 15.38%,11.54%,7.69%and 1.54%.According to the calculation results of dilution rate,A scanning speed of 400 mm/min is appropriate. |
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