Study On The Residual Stress And Friction And Wear Properties Of 316L Stainless Steel By Laser Impact Forging

Laser impact forging technology covers a wide range of subjects,compared with laser impact strengthening technology,laser impact forging technology has a better effect in reducing defects in cladding parts,such as shrinkage cavity and crack,and improving the overall performance of formed parts in terms of changing residual stress,microstructure and original defects in materials,it can also change the size and distribution of the residual stress of the forming part.316 L stainless steel has good toughness and plasticity,and is widely used in all walks of life.In the course of service,it us ually occurs fracture,wear and fatigue damage,so it is urgent to study its internal properties and microstructure.In this paper,316 L stainless steel is used as the experimental material.By using ABAQUS finite element simulation platform and laser impact forging composite additive manufacturing experiment,the effect of laser impact forging parameters on the residual stress of 316 L stainless steel is explored,and the internal properties and microstructure of laser impact forging 316 L stainless steel cladding parts are studied through the laser impact forging composite additive manufacturing experiment.The main research work and content of this paper are as follows:This paper introduces the basic process of laser impact forging with the aid of ABAQUS finite element analysis simulation platform,the establishment of the finite element analysis model of laser impact forging and the setting of parameters.By changing the impact times and peak pressure in the parameters of laser impact forging,the change of residual stress of materials is observed.The effect of lap ratio on the residual stress and the effect of peak pressure and impact times on the residual stress are studied under the multi-point lap model.The simulation results show that with the increase of peak pressure and impact times,the residual compressive stress in the material is also larger,and at 50% lap ratio,the deeper the depth is,the greater the residual compressive stress will increase and then decrease.At 30% lap ratio,the farther away from the center of the spot on the material surface,the smaller the residual compressive stress is.The experiment plan of laser impact forging was designed,and the experiment of impact forging 316 L stainless steel was carried out.In the experiment,XL-640 type X-ray stress tester was used to measure the residual stress of the forged parts;HVS-1000 Z type microhardness tester was used to measure the hardness of the formed parts,and the metallographic samples were polished by the metallographic grinding machine;20BD type metallographic microscope was used to analyze the microstructure of the samples.The experimental results show that the residual stress of laser melted deposition specimen and laser impact forging specimen are tensile stress and compressive stress respectively,and the stronger the laser energy is,the greater the residual compressive stress is.The laser impact forging process effectively improves the residual compressive stress of the material,and the distribution trend of the residual stress in the direction of the depth of the cladding layer is consistent with the simulation results.With the increase of laser energy and repetition frequency,the surface hardness of the material becomes larger and deeper.The hardness values of laser melted deposition samples and laser impact forging samples first increase and then decrease,and laser impact forging can well increase the effective hardened layer depth of the formed parts.The internal defects of laser impact forging specimens are much less than that of laser melted deposition specimens.The defects such as pores and cracks in laser melted deposition specimens can be greatly reduced by laser impact forging technology.The range of grain size of laser melted deposition sample is 10-40 μ m,and that of laser impact forging sample is 5-20 μ m,which shows that laser impact forging technology can effectively refine the grain size of the structure.There are many columnar crystals with smaller size,which are divided by more acicular crystals and some columnar crystals.In the experiment,the Bruker UMT-Tribolab friction and wear tester was used to test the friction and wear of laser melted deposition sample and laser impact forging sample,and the friction coefficient was measured in real time.The width and depth of wear mark were observed by white light interference instrument,and the wear amount and wear rate were obtained by formula.The experimental results show that the friction coefficient fluctuates in a small range.With the increase of laser energy and repetition frequency,the friction coefficient,wear mark width and depth,wear amount and wear rate of 316 L stainless steel are significantly reduced.The results show that the laser impact forging process can significantly enhance the wear resistance of the laser melted deposition specimen,and the laser impact forging 3D parts can be applied to the important functional moving parts field.