Study On The Inhibition Mechanism Of Laser Remelting Process Parameters On Micro Defects Of Fe Based Ni/WC Coating

The lose efficacy of most parts was caused by wear,corrosion,crushing and distortion or even fatigue fracture on the surface of the part.It started from the surface and slowly spreaded to the interior,and gradually became a trace of all kinds of crack sources,which eventually caused the whole part to be discarded.However,the use of plasma spraying and laser remelting composite technology to strengthen the substrate surface treatment can effectively improve the wear resistance,high temperature resistance and surface erosion resistance performance,in which prompt more high melting point and high hardness materials were widely used,and broaden the scope of useful materials.In this paper,a Fe-based Ni/WC coating was prepared on the surface of 45 steel using plasma spraying equipment,followed by laser remelting treatment.Then the three-dimensional finite element analysis model was established.The influence of process parameters on the variation of temperature field in laser remelting process was discussed.The interface behavior of the process parameters optimization of the laser remelting Fe based Ni/WC ceramic coating was studied.A prediction model of laser remelting process parameters and coating porosity was established by the Response Surface Method.The main research results include the following aspects:?1?The thermal structure coupled with the basic theory of finite element method was used to apply the reasonable thermal boundary conditions.The thermal physical parameters of the corresponding materials were calculated,and the Gauss moving heat source model was selected.The three-dimensional temperature field model of laser remelting was established by ANSYS finite element software.The change of temperature field in laser remelting process under different laser process parameters was obtained.It provided theoretical support for the optimization of experimental process parameters in the subsequent chapters..?2?Using SEM equipment,it was found that there were larger pores and obvious interlayer cracks on the interface of sprayed coatings,which was characterized by mechanical bonding.After laser remelting treatment,the interface structure was reticular and well-developed dendrite structure.The metallurgical bonding between coating and matrix was formed;XRD equipment detected spray coating not only includes[Fe,Ni],Cr and WC phase but also contains Cr₇C₃,Fe_0.04Ni_0.36.36 and other hard phase.After the remelting of different process parameters,new phases such as Fe₂Si,Cr₂Si,and W₂C appear.Moreover,the phase composition in the remelted layer has almost no change.The faster the scanning speed,the smaller the half-height,the smaller the grain size,the more obvious the grain refinement,and the greater the corresponding micro-hardness?the maximum micro-hardness increased by47%?.The measured dendrite spacing decreases with increasing scanning speed,and the coating and matrix elements diffuse into each other.?3?The experimental program of laser remelting coating porosity under various process parameters?laser power P,scanning speed V and spot diameter D?was established by response surface methodology,which was used to test and obtain the response value data.The two multiple regression equation model of the process parameters and the porosity Y was obtained.Finally,the optimum process parameters obtained by the equation are the laser power of 600w,the scanning speed of 150mm/min,the spot diameter of 2mm,and the minimum porosity of about 0.28%.