| Gears are the core components of the mechanical transmission system,they not only bear alternating loads during service,but are also subjected to severe shock loads,abrasion,corrosion and other harsh working conditions,which brings great challenges to the strengthening of gears.This article takes 20Cr2Ni4 A alloy steel commonly used in gears as the research object,and uses laser shock peening to implant nanodiamond onto the material surface,the strain strengthening and fine-grain strengthening formed by laser shock peening and the second phase strengthening brought by nanodiamond are used to improve the mechanical properties of 20Cr2Ni4 A alloy steel.On this basis,combined with carbonitriding to develop a composite strengthening process,the high-density dislocations and the increased number of grain boundaries introduced by laser shock peening provide microscopic channels and adsorption centers for carbon and nitrogen atoms,thereby increasing the velocity of infiltration and the thickness of the carbonitriding layer to achieve compound strengthening of 20Cr2Ni4 A alloy steel.The result shows:(1)The laser shock peening can implant about 100 nm diamond particles onto the20Cr2Ni4 A alloy steel surface to form a composite strengthening layer.Laser shock peening causes a strong plastic deformation on the material surface and introduces a residual compressive stress about-267 MPa to form a strengthened layer about 1000μm.The mechanical properties of the material are significantly improved.After the implantation of diamond particles,the defects such as surface roughness caused by laser shock peening were reduced.The surface roughness of the material was 2.25μm,which was reduced by 55.53% compared with the sample treated by laser shock peening.Compared with the original sample,the Vickers hardness of the material increased from 160 HV to 212 HV,which is an increase of 32.5%,the nano-hardness and elastic modulus were 4.93 GPa and 208.63 GPa,increased by 31.11% and 15.72%,respectively,and the maximum contact depth was reduced from 148.47 to 124.14 nm,which is a decrease of 16.39%.Due to the implantation of diamond particles,a self-lubricating strengthening layer is formed on the material surface,which provided a function similar to a sliding bearing during the friction process,which reduces frictional resistance.And the wear mechanism changes from abrasive wear to a mixed mechanism of adhesive wear and abrasive wear.The friction coefficient of material is reduced from 0.50 to 0.31,and the wear loss is reduced from 8mg to 4mg,which is a50% reduction.(2)On the basis of the implantation of diamond particles by using laser shock peening,a composite strengthening process was developed in combination with carbonitriding.After composite strengthening,the metallographic structure of20Cr2Ni4 A alloy steel changes from ferrite and a small amount of pearlite to nitrogen-containing acicular martensite and retained austenite,as well as a small amount of granular carbonitride.The surface hardness of the carbonitriding layer changes with the increase of laser energy,up to 858 HV,which is 4.36 times higher than the original sample.The friction coefficient of the material is reduced from 0.74 of the sample after carbonitriding to 0.24.The volume removal of the sample with diamond implanted in composite strengthening reaches the minimum.As a result,laser shock peening as a pretreatment can improve the strengthening effect of carbonitriding,and nanodiamond can effectively improve the wear resistance of the carbonitriding layer. |
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