| Modern machining is constantly developing in the direction of ultra-precision,ultra-high speed,and high intelligence.In this case,the material performance,accuracy,and durability of mechanical parts must be continuously improved to ensure that each part is not easily disabled or damaged during work.42CrMo steel gears,rear axles,connecting rods and other parts must work in a very heavy load environment,which causes these parts to be prone to wear and thermal fatigue and lose accuracy or damage.In order to improve the hardness and wear resistance of these parts,increase their effective life,reduce costs,and enable them to work in more harsh environments,the use of laser cladding technology to strengthen and repair the surface of parts has significant economic benefits.In this paper,the surface modification of 42CrMo steel material is used as a research background.Using semiconductor laser cladding,Ni60 alloy coating,Ni60+nano-WC composite reinforced coating and Ni60+nano-WC+CeO2 composite were prepared on 42CrMo steel surface.Modified and strengthened coating,systematically studied the structure and related mechanical properties of the three coatings based on Ni60 powder,and analyzed the effect of ceramic powder nano-WC and rare earth oxide CeO2 on the coating structure and performance.In order to obtain the optimal process parameters of laser cladding Ni-based coatings,through the study of the forming quality,microstructure,microhardness and wear resistance of Ni60 cladding layer under different process parameters,the results show that the Ni-based composite powder The optimal process parameters are:laser power is 1800 W,scanning speed is 2 mm/s,spot is circular and diameter is 5 mm,preset powder thickness is 2 mm,protective gas flow rate is 10 L/min,overlap rate is 45%.These process parameters can obtain a cladding layer with a large area,good combination with the matrix material,few defects such as cracks and pores,and good performance.The microstructure of Ni60 cladding layer is mainly composed of dendrite,block,strip and short rod.The coating phase is mainly dominated by γ-Ni(Fe)solid melt.In addition,compounds such as FeNi3,M23C6 and(Fe,Ni)3B are also produced.At a constant scanning speed of 2 mm/s and a laser power of 1800 W,the cladding layer generally shows a higher hardness value,up to 780 HV0.2,which is 180%higher than the hardness of the substrate;under the same process parameters,Ni60 The cladding layer also showed the best wear resistance.The frictional mass loss of the sample in 20 minutes was 71.2 mg,and the average value of the friction coefficient curve was 0.506.Compared with the matrix wear and friction coefficient,both were greatly improved.In order to enhance the hardness and wear resistance of the Ni60 alloy cladding layer,Ni60 reinforced coatings containing 0%,10%,20%,30%and 40%nano-WC powder were prepared on the substrate surface.The experimental results show that the surface of the nano-WC reinforced Ni60 coating is well formed.The morphology of the reinforced coating is strip-shaped,dendritic,fishbone-shaped,massive and granular.The phase is dominated by Ni-Fe phase,part of nano-WC remains,and part of it forms a new W2C phase.In addition,composite carbides such as Fe3C,Cr23C6,M6C,SiC,Cr7C3,and boron such as CrB,Fe3B are also formed in the coating Compounds and tungsten compounds such as Si2W and NiW.The micro-hardness of nano-WC reinforced coating can reach up to 1256 HV0.2,which is about 50%higher than that of Ni60 alloy coating.The minimum average friction loss of the reinforced coating is 10.2 mg,which is only 1/7 of the Ni60 alloy coating;the average friction factor of the reinforced coating can be as low as 0.275,and the average friction factor of the Ni60 alloy coating is 0.530,a reduction of about 48%.Nano WC enhanced coating wear mechanism is mainly adhesive wear,but also accompanied by slight abrasive wear.In order to further study the structure and properties of rare earth doped composite modified nano-WC reinforced nickel-based coatings,0%,0.5%,1.0%,1.5%,and 2.0%CeO2 composite-reinforced nano-WC were prepared on the surface of 42CrMo steel/Ni-based coating.The results show that:adding rare earth CeO2 can make the coating surface without cracks,and can effectively reduce the number of pores in the coating.The coating phase modified by the rare earth CeO2 composite uses y-Ni(Fe)solid melt as the matrix phase.Part of the WC residue and new phase W2C are generated in the coating.In addition,Fe3C,Cr23C6,M6C M=W,Fe,Ni),SiC,Cr7C3 composite carbides,Si2W,NiW tungsten compounds,CeFe2 and CeNi2 containing Ce elements and other complex compounds.The structure of the rare earth CeO2 composite modified coating is mainly composed of dendrites,cell crystals,strips and blocks.When the addition amount of rare earth CeO2 is 1.0%,the reinforced phase of the composite modified coating is uniformly dispersed and the structure is significantly refined The coating structure is more dense.At the same time,the maximum hardness of the coating is 1560 HV0.2,which is an increase of about 20%compared with the maximum hardness of the CeO2 coating without adding rare earth.The appropriate amount of CeO2 composite modified coating has a minimum wear of 6.1 mg and a minimum friction factor of about 0.23,which is lower than that of the coating without CeO2 composite modification.The wear mechanism of the rare earth CeO2 composite modified coating is mainly abrasive wear,and the adhesion wear is supplemented by the composite wear mechanism. |
PDF Full Text Request