| Alloy steel is a widely used steel material in the mechanical parts manufacturing industry.Due to the relatively low cost of alloy steel and its high plasticity,toughness and wear resistance,alloy steel is widely used to manufacture parts and components in mechanical equipment.In recent years,due to the development of technology,the power of various mechanical equipment has gradually increased,and the performance of parts made of alloy steel cannot fully meet the needs of the current mechanical industry.Preparing a high-performance protective coating on the surface of alloy steel mechanical parts is a technology that effectively improves the performance and life of the parts.Alloy steel parts are damaged in a variety of conditions in industrial production,such as wear failure and fracture failure.Simply improving a property of alloy steel is not enough to improve the overall life of alloy steel parts.Research and preparation of protective coatings that can simultaneously improve the wear resistance and mechanical properties of alloy steel is of great significance to the machinery industry.In nature,many organisms have special structures,and these biological structures can achieve good results with less biological materials.Gradient structure is an excellent biological structure.It combines materials with different mechanical properties to produce a structural gradient inside the material.Gradient structures can adapt to different characteristics(such as elastic modulus and strength)between different materials,and provide toughness,wear resistance and prevent crack propagation.The application of bionic gradient structure to alloy steel components can effectively improve the mechanical properties and wear resistance of alloy steel components.This article takes 40 Cr alloy steel,which is commonly used in industry,as the research object,and takes the typical biological gradient structure-dog teeth as a biological model of bionic design,and uses laser cladding technology with low heat input,small deformation,and easy metallurgical combination with the substrate as protection.The preparation method,and the TiC ceramic material was selected as the hard and strengthening phase of the protective coating.A bionic gradient cermet protective coating was designed and manufactured on the surface of the alloy steel.The prepared bionic gradient coating has the characteristics of simultaneously improving the wear resistance and mechanical properties of alloy steel,and has the advantages of simple manufacturing process,good metallurgical bonding inside the coating,and no cracking.The main research contents are as follows:(1)Reveals the composition of the gradient structure in dog teeth and designs a high-performance bionic gradient coating model suitable for alloy steel metal surfaces.The enamel to dentin of dog teeth is gradually reduced,and the content of hydroxyapatite in the hard phase gradually decreases.The tooth structure also changes from compact to loose.The bionic gradient coating model designed for the alloy steel metal surface based on the dog's tooth gradient structure is mainly composed of the outermost layer with high hardness and strength,the innermost layer with high toughness,and the middle with moderate properties.The three layers that make up the coating structure allow the gradient coating to achieve both high hardness and high toughness.(2)The effects and mechanisms of different TiC preparation processes and different TiC contents on the microstructure and properties of laser cladding 40 Cr gear steel coatings under the same laser energy conditions were revealed.With the same laser energy,externally cladding TiC is more effective than in-situ synthesis.Due to the highest TiC content in the hard phase of the coating,the 50% TiC coating applied by laser has the highest microhardness value(922HV),the lowest abrasion loss weight(1.2mg),and the best wear resistance.When the laser cladding process is used to prepare the gradient coating,the additive method is more suitable for preparing the gradient coating than the in-situ synthesis method.(3)The characteristics and advantages of gradient coatings are revealed.The gradient coating has a reasonable gradient of the composition of the cladding layer,which can promote all TiC particles to enter the coating,the roughness of the coating surface is low,and the overall micro hardness and coating thickness(739 ?m)of the gradient coating are significantly higher than both Quality coating.The surface roughness of the homogeneous coating is high,the content of TiC particles entering the coating is low,and the cladding layer with the same TiC content can not significantly increase the overall thickness of the coating(518 ?m).Gradient TiC coatings have good metallurgical bonding and no cracks,indicating that the gradient structure solves the process of cracking in high TiC content coatings.(4)It was revealed that the TiC content in the pre-prepared powder for the gradient coating will obviously change the microstructure and microhardness distribution inside the gradient coating.When the TiC content in the pre-prepared powder for preparing the gradient coating is high,the TiC inside the coating will all form a TiC dendrite structure;when the TiC content is small,the TiC inside the coating will all form a TiC particle structure.The maximum microhardness of TiC dendritic gradient coating is 1243 HV,and the maximum microhardness of TiC granular gradient coating is 1083 HV.The overall microhardness of the TiC dendritic structure gradient coating is higher than that of the TiC granular structure gradient coating,because dense TiC dendritic structure increases the microhardness more significantly than the TiC granular structure.(5)Revealed the different mechanisms of TiC dendritic structure gradient coating and TiC particle structure gradient coating to enhance mechanical properties such as impact toughness and mechanical fatigue performance.The TiC dendrite structure inside the TiC dendrite gradient coating significantly improves the impact toughness of the gradient coating due to its high strength.The TiC dendrite structure promotes the impact fracture crack to show a certain degree of deflection in the macroscopic extension of the coating,thereby Energy for crack propagation is consumed.However,when the impact fracture crack passes through a single TiC dendrite in the microstructure,the fracture crack is not deflected.TiC particles have a more uniform distribution of TiC particles inside the gradient coating,which promotes higher levels of macro-and micro-deflection of fracture cracks and consumes more crack propagation energy,thereby achieving the highest impact toughness.The mechanical properties of TiC granular gradient coatings are better than TiC dendritic gradient coatings.This shows that TiC granular structure gradient coating is more suitable for impact resistance and fatigue resistance coating of alloy steel.(6)Reveals the wear behavior and strengthening mechanism of TiC dendritic structure gradient coating and TiC granular structure gradient coating under depleted lubrication wear environment,dry friction wear environment and heavy load wear environment.In the three friction and wear environments,the friction coefficient and the weight loss of the dendritic gradient coating are lower than those of the granular gradient coating.TiC on the surface of the dendritic gradient coating forms a grid-like unit,and TiC on the surface of the granular gradient coating forms a round particle unit.The high hardness and high coverage area of the TiC grid-like unit body lead to less plastic deformation and less wear of the dendritic gradient coating.The TiC round particle unit body has fewer areas for strengthening the coating and is easier to peel off.The wear performance of TiC dendritic structure gradient coating is better than that of TiC granular structure gradient coating under various wear conditions.Moreover,the TiC grid-like unit body on the TiC dendritic structure gradient coating surface has stronger coating strengthening ability.This shows that TiC dendritic structure gradient coating is more suitable for wear-resistant coating of alloy steel.In this paper,by comparing the mechanical properties and wear properties of TiC dendritic structure gradient coating and TiC granular structure gradient coating,it is revealed that the mechanical properties of TiC dendritic structure gradient coating are better,and the wear performance of TiC granular structure gradient coating is better..It provides experimental basis,technical and theoretical references for the development of alloy steel protective coatings with excellent properties. |
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