| As the most commonly used material in the field of machinery manufacturing,alloy steel has good plasticity,toughness and excellent machining performance,and is widely used in the manufacture of large parts in machinery and equipment.When the alloy steel mechanical parts are in service in a complex and harsh working environment,they will be damaged by various damages such as uneven stress,alternating cold and heat,etc.This will not only affect the working accuracy of the mechanical equipment,damage its normal operation,and even worse Will greatly affect the economic benefits of the machinery manufacturing industry.The failure of alloy steel mechanical parts is usually caused by various defects on the surface.Therefore,strengthening the surface can effectively improve the mechanical properties while reducing defects,thereby prolonging their service life and improving it to a greater extent.Economic benefits.Among the many surface strengthening treatment methods,the most widely used in the field of mechanical parts manufacturing and repairing is the use of laser cladding technology to fuse metal-based ceramic powder on the surface of the substrate to form a high-quality metal-ceramic composite coating.This coating cleverly combines the excellent mechanical properties of metal materials with the excellent properties of ceramic materials such as high hardness and high wear resistance,so that the substrate can obtain a metallurgical coating with high bonding strength,and the surface wear resistance is also effectively improved.However,while the wear resistance of alloy steel is improved,the toughness of the coating part will be reduced,which has a negative effect on improving the service life of alloy steel parts.However,gradient coating can not only improve the overall mechanical properties of the material,but also solve the problems of holes and cracks in the coating due to the large difference in physical parameters between the coating and the base material.Therefore,the study of a gradient coating structure that can improve the overall mechanical properties of materials is of vital significance to the mechanical parts industry.In this paper,40 Cr alloy steel commonly used in machinery manufacturing is used as the base material,WC is selected as the hard strengthening phase in the coating,laser cladding technology is used,and appropriate laser processing parameters are selected,and the cermet gradient and cermet are prepared on the surface.Non-gradient coating.The effects of the number of cladding layers and ceramic hard phase content on the phase composition,microstructure,microhardness,friction properties,impact properties and tensile properties of alloy steel are revealed.The results are as follows:(1)The main phase composition,microhardness and microstructure of Fe-WC gradient coating are studied.The main phase composition of the coating is ferrite,Fe3 C,WC and W2 C.However,due to the different WC content of each coating,the content of each phase is also different.As the WC content in the sample increases,the hardness also increases.WC improves the microhardness of the cladding layer.In the layer,a large amount of WC dendritic structure covers the surface of the material,and the microhardness is increased by 3 times.(2)The mechanism of the influence of Fe-WC gradient coating on the surface wear resistance of alloy steel is revealed.The single-layer coating has less WC content on the surface,low aggregation,and its cladding layer is shallow,and the surface hardness improvement effect is not good,and the increase in hardness also reduces the toughness of the material.Due to the excessive thermal stress in the cladding process and the large amount of powder splashing in the non-gradient coating,the WC melted on the surface of the substrate is less,and the quality of the resulting coating is poor.In contrast,in a gradient coating,the WC content in the cladding layer changes gradually,which is conducive to the expansion of the bonding zone and the heat-affected zone,forming dense,wide-covered and uniformly distributed WC particles,and improving the surface resistance of the material.Abrasiveness.(3)The mechanism of the influence of Fe-WC gradient coating on the mechanical properties of alloy steel is revealed.Compared with the three-layer gradient coating,the five-layer gradient coating has a deeper molten pool,and the WC dendritic structure has a gradient distribution in the longitudinal direction of the coating,the distribution is more uniform,and the density is higher.When subjected to transverse or longitudinal loads,the dense and uniform WC can effectively inhibit the propagation of cracks,promote the cracks to extend along the WC grain boundaries,and improve the mechanical properties of the material. |
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