Research On The Formation Mechanism Of Modified Layer Prepared By Laser Shock Melt Injection Fine Wc_p In Titanium Alloy And Its Wear Resistance

The wear-resistant modification technology of titanium alloy is a research topic in the application field of titanium alloy for a long time.In this paper,based on the review of related research status at home and abroad,combined with the previous research results of the research group,a new idea is proposed to prepare WC_p gradient wear-resistant modified layer in situ on the surface of titanium alloy by using laser shock melt injection fine particles technology,which can ensure that the modified layer has sufficient thickness and binding force.At the same time,it can realize the multi-component synergistic wear resistance modification of titanium alloy by taking advantage of the synergy of the high-energy quick-cooling characteristics of laser processing technology,the grain refinement effect of fine particles,and the high hardness and high wear resistance of ceramic materials.In the research,TC11 titanium alloy,which is widely used in aerospace industry,is taken as the object.Through the establishment of the energy model of the formation process of the fine particle modified layer,the study of the process of the fine WC_p modified layer and the analysis of the microstructure of the fine WC_p modified layer,the formation mechanism of the fine WC_p modified layer of the titanium alloy is clarified.Si₃N₄ is taken as the abrasive.The friction and wear behavior of WC_p modified layer and its mechanism were investigated,which not only provided the realization method and theoretical basis for the wear resistance of titanium alloy,but also enriched and developed the new technology of laser shock melt injection fine particles.The main work and achievements of this paper are as follows:?1?According to the technical principle of laser shock melt injection fine particles,the energy model is established by considering the energy of fine particles injection,the temperature rise of fine particles in the process of injection and the formation of molten pool on the surface of matrix material.Based on the model,the influence of particle size on energy is discussed.The established energy model can provide an important reference for the selection of laser process parameters under given experimental conditions.At the same time,under the research conditions of this paper,the particle size and the specific energy of the laser show an"L"type relationship curve.With the increase of particle size,the specific energy decreases until it tends to be stable.Considering the two factors of energy and particle size,it is more appropriate to select fine particles with a particle size of 1?m.?2?The temperature field model of WC modified layer prepared by laser shock melt injection fine particles on TC11 was established using Abaqus software.The simulation results of the temperature field are compared with the experimental results to verify that the three-dimensional transient temperature field can accurately reflect the temperature distribution law.At the same time,based on the analysis results of the temperature field and energy model,the laser process parameters were further optimized through the orthogonal test Methods.The evaluation index defect grade Q and molten pool depth D were given different weights by the comprehensive evaluation method.The influence degree of the process parameters on the comprehensive evaluation was obtained,that is,laser power>defocusing amount>scanning speed.The better laser process parameters under the research conditions were determined as follows:laser power 400W,Scanning speed 80mm·min^-1,defocus amount-1mm.?3?The microstructure of the upper part,the middle part,the lower part and the joint with the matrix of the modified layer were studied.The hardness change of the surface and cross section of the modified layer was also investigated.Finally,the influence mechanism of fine WC_p on the structure and hardness of the modified layer was discussed.The results show that the matrix morphology of the upper and upper middle part of the modified layer is fine cellular structure,and the obvious transition layer can be seen in the lower middle part of the modified laye.The matrix structure of the lower part of the transition layer is mainly dendrite.At the same time,the average hardness of the surface of the modified layer is 749.4HV,and the hardness peak value of 892.9HV appears in the middle part of the modified layer with more WC particles.The average hardness of cross section is about 2.28 times that of matrix.In addition,WC particles are mostly distributed in the grain boundary in the upper part of the modified layer,and are mostly distributed in the crystal in the lower part of the modified layer,which is directly related to the different temperature of WC particles injected into the molten pool caused by the characteristics of laser shock melt injection technology.?4?The friction and wear behavior of the modified layer of WC_p at room temperature was investigated with Si3N4 as the grinding material,and compared with the friction and wear behavior of TC11 titanium alloy under the same conditions.At the same time,the mechanism of multiple cooperative strengthening of WC_p modified layer is preliminarily explored.The results show that the wear resistance of the modified layer is better than that of TC11,and its specific wear rate is 0.058?m³/N?m,while that of TC11 is 0.20?m³/N?m;the wear mechanism of the modified layer is mainly delamination wear with slight abrasive wear,while that of TC11 is mainly abrasive wear and adhesive wear.The analysis shows that the reason for the improvement of the wear resistance of the modified layer lies in the change of wear mechanism,the wear resistance and friction reduction of WC particles,and the gradient structure and the in-situ generation method that are beneficial to the overall structural strength of the modified layer.