Study On Preparation And Performance Of Wear-resistant Modified Layer On Titanium Alloy Surface

In this thesis,laser cladding process was used to prepare B₄C reinforced Fe/Cr-based composite coating on the surface of TC4 alloy,and the influence of different laser process parameters on the structure of the cladding layer was studied.The amount of B₄C added to the structure,mechanical properties and mechanical properties of the laser cladding layer was studied.The effect of dry sliding friction and wear properties and the effect of annealing process on the dry sliding friction and wear properties of laser cladding layers,the research results are as follows:Different process parameters are used for laser cladding of high-carbon ferrochrome powder to test the hardness,dilution rate,thickness,and overlap rate of the coating.The results show that when the power is 2000 W,the cladding speed is 5 mm/s,and the powder feeding rate is 14 g/min,the macroscopic hardness of the cladding layer can reach 63.54HRC,the dilution rate is 19.6%,and the microstructure is uniform and fine.When the overlap rate is 35%,the coating is smooth.Therefore,the above parameters are used as the best parameters for the subsequent addition of B₄C powder for cladding.The main products of high-carbon ferrochromium as cladding powder are hard phase Cr₂₃C₆,Ti C and solid solution Fe-Cr.After adding B₄C powder,the hard phase Cr B and Ti B₂ are added to the cladding layer.The macroscopic hardness values of the laser cladding layer with B4C addition of 0%,15%,and 30%are 63.54 HRC,69.76 HRC,and 73.75 HRC,respectively.In terms of the stability of the friction coefficient,the average friction coefficient of the laser cladding layer without B₄C added fluctuates between 0.488 and 0.776,and the friction coefficient of the laser cladding layer with 30%B₄C addition fluctuates in the range of 0.376 to 0.516.The amplitude is only 0.140,which effectively improves the friction stability of the laser cladding layer.From the perspective of wear resistance,the addition of B₄C can improve the wear resistance of the laser cladding layer.Especially under high load,the laser cladding layer with 15%B₄C addition has the smallest loss rate and has relatively stable wear performance.Under low load,the surface of the laser cladding layer with B₄C added is slightly abraded.When the load increases,the surface of the laser cladding layer with B₄C addition of 30%begins to experience severe peeling and abrasion.Under the same load,B₄C is added.The surface of the laser cladding layer with an amount of 15%suffers the least abrasion.When the load is 120 N,the laser cladding layer with 30%B₄C addition has micro-cracks on the wear surface.The micro-cracks will propagate in the subsequent wear process and cause hidden dangers of material failure.As the load increases,the thickness of the hardened layer on the grinding surface increases.The hardness of the laser cladding layer annealed at 500?and 900?has a certain degree of decrease,respectively 66.48 HRC and 64.07 HRC.The 500?annealing process can effectively improve the stability of the friction coefficient of the laser cladding layer,and the variation range is only 0.364?0.578,especially the wear resistance under high load.When the load is 120 N,the wear rate of the laser cladding layer annealed at 500?is1.510×10^-6 g/m,and the wear rate is reduced by 33.16%.The annealing process effectively reduces the degree of wear on the wear surface.Under low load,it is mainly mild wear and oxidative wear,and under high load,peeling wear and oxidative wear occur.The thickness of the hardness-enhanced layer of the annealed laser cladding layer increases with the increase of the load.When the load is 120 N,the thickness reaches 50?m.