Study On Laser Surface Strengthening Process And Surface Integrity Of Cemented Carbide

Laser micro-nano processing has become an important research direction for domestic and international research.Laser impact strengthening technology is a technique that uses a short pulse laser beam to interact with materials to modify the surface of metallic materials through induced shock wave pressure.This technology has both impact deformation effect and impact strengthening effect,which can realize the control of the surface geometry and physical properties as well as the internal organization of the material.It has great potential applications in improving tool performance.Therefore,this paper takes cemented carbide tools as the research object and studies the effect of laser strengthening process on the surface structure and properties of tool materials from the mechanism of laser action on cemented carbide,and analyzes the effect at the micro level.The study covers the following main areas:Firstly,the experimental platform of laser impact strengthening is built based on the mechanism of laser surface modification technology.The effects of different laser process parameters on the surface microscopic morphology and elemental changes of cemented carbide materials were analyzed using scanning electron microscopy,energy spectrum detection instruments and white light interferometer.The increase of laser power within the strengthening threshold can lead to the refinement of carbide surface grains and the stacking of surface dislocations,which are the main reasons for the influence of its surface residual stress and microhardness.Among them,the scanning speed affects the mass fraction of Co elements on the carbide surface,and multiple impacts on the carbide surface can change its surface roughness by surface remelting phenomenon.Covering the material surface with a black absorption protective layer and a water-constrained layer can effectively improve the shock wave peak pressure and protect the surface elements.Theoretical support is provided for the study of the effect of laser process parameters on the surface strengthening of cemented carbide.Secondly,according to the relationship equation of laser impact strengthening principle and material elastic limit deformation,the mathematical model of laser shock wave superposition and material plastic inhomogeneous deformation is established.The laser impact strengthening simulation process was also implemented based on Comsol simulation software.The results of the simulation of the residual stress field revealed that the laser power is the biggest factor affecting the residual stress on the surface of cemented carbide;analyzed from the perspective of the definition of microhardness,the change trend of microhardness is about 3 times of the yield stress,and it is known from the yield stress field after laser impact strengthening that the number of laser impacts has the most obvious effect on the change of its microhardness.Finally,based on the results of the simulation data,laser process parameter strengthening orthogonal experiments were conducted to measure the residual stress and microhardness using XRD and Vickers microhardness tester.The laser power had the most significant effect on the surface roughness of carbide after laser strengthening,and the minimum value of surface roughness after laser impact strengthening was Ra=0.0048?m and the maximum value was Ra=0.0707?m;The residual compressive stress induced by laser on the surface layer of carbide could reach the maximum of-958.98 Mpa,and black pores appeared on the surface after the evaporation of Co as the bonding agent of carbide material.The remaining WC phase under the action of laser shock wave undergoes displacement collision,which leads to the generation of residual compressive stress;the microhardness of the cemented carbide surface after strengthening increases by 48% compared with that before strengthening,the WC phase grain refinement occurs after impact strengthening and the loss of Co elements by vaporization,the WC hard phase is harder than the Co bonding phase,thus the increase of surface microhardness;Based on the test and inspection results,a stepwise regression prediction model was established to optimize the data using Matlab particle swarm algorithm with residual stress and microhardness as the optimization indexes,and a set of optimal laser process parameters within the strengthening threshold were obtained.