Effects Of Laser Shock Peening On Cavitation Erosion And Cavitation-Silt Erosion Resistance Of 2Cr13 Stainless Steel

2Cr13 stainless steel is widely used in flow-parts such as steam turbine blades and turbine impellers.Cavitation erosion(CE)seriously endangers the fluid machineries.In addition,cavitation couples with the particles to erode the flow-parts.Laser shock peening(LSP)can induce a compressive residual stress layer and refine grains,which has the potential to slow down CE and cavitation-silt erosion(CSE)of 2Cr13 stainless steel.In this work,theoretical calculations were used to design the experimental parameters and support numerical simulation.The stresses and strains of 2Cr13 stainless steel after different LSP coverage layers were simulated by finite element analysis.The changes in surface integrity of specimens before and after LSP were studied.The mechanisms of LSP on CE and CSE were revealed by cumulative mass losses and erosion behavior observations.The main research contents are as follows:(1)The experimental parameters of LSP were determined through theoretical calculation.The ABAQUS finite element software was used to simulate residual stresses and strains of one coverage layer(LSP-1),two coverage layers(LSP-2)and three coverage layers(LSP-3)LSP specimens and 2Cr13 stainless steel was subjected to LSP with one and two coverage layers.The calculated LSP parameters included impulse energy of 10 J and spot diameter of 2 mm.The simulated average residual stresses of LSP-1?LSP-2 and LSP-3 specimens were-366 MPa?-385 MPa and-387 MPa.The compressive residual stress depths of three specimens were 0.75 mm,1.0 mm and 1.1 mm.However,the surface strains of three specimens were 3.5 ?m,6 ?m and 9 ?m.The results showed that the surface compressive residual stresses,the depths of the compressive residual stress layer and the surface strains increased with increasing LSP layers.In addition,minor improvement was achieved with LSP-3 compared with LSP-2.The results of the residual stress tests were consistent with that of the numerical analysis.(2)The changes of grain size,microhardness and surface roughness before and after LSP were studied.The results showed that LSP can refine grains,induce a plastic deformation layer and increase microhardness and roughness.Original grains with an average size of 20 ?m were refined into 15 ?m(LSP-1)and 10 ?m(LSP-2).LSP also induced a plastic deformation layer with the depth of 80 ?m(LSP-1)and 100 ?m(LSP-2).The microhardness increased from 270 HV(non-treated)to 310 HV(LSP-1)and 330 HV(LSP-2).The roughness of the non-treated,LSP-1 and LSP-2 specimens along the direction of the micro grooves was Ra 0.139,Ra 1.436 and Ra 2.388.The roughness of the three specimens along the direction perpendicular to micro grooves was Ra 0.236,Ra 1.807 and Ra 2.465.(3)The non-treated,LSP-1 and LSP-2 specimens were tested in cavitation environment and the effects of LSP on the CE resistance were studied.The results showed that LSP prolonged the incubation period,reduced the mass losses,and increased the CE resistance of 2Cr13 stainless steel and the CE resistance of LSP-2 specimen was better than that of the LSP-1 specimen.The mass losses of the non-treated,the LSP-1 and LSP-2 specimens were 7.88 mg,7.19 mg and 6.48 mg.During the incubation period,the plastic deformation of the micro groove alleviated with increasing LSP layers.During the acceleration period,the direction of crack propagation tended to be consistent and the material exfoliation was alleviated with increasing LSP layers.During the recession period,the surface integrity increased with increasing LSP layers.After LSP,the refined grains withstood more cavitation deformation and increased the resistance to cavitation crack growth.The residual compressive stress layer can reduce the amplitude of stress intensity factor of the cavitation crack tip and reduced the crack growth rate.(4)The non-treated,LSP-1 and LSP-2 specimens were tested in CSE environment with different particle diameters and the effects of LSP on the CSE resistance were studied.The results showed that LSP reduced the mass losses and increased the CSE resistance of 2Cr13 stainless steel and the CSE resistance of LSP-2 specimen was better than that to the LSP-1 specimen.In 0.02 mm particle-water mixture,the mass losses were reduced from 11.28 mg(non-treated)to 10.60 mg(LSP-1)and 9.70 mg(LSP-2).The failure forms of the non-treated specimen were erosion wear,abrasive wear,plastic deformation and cavitation damage.However,the failure forms of the LSPed specimens were erosion wear,abrasive wear and cavitation damage.The number and the diameter of micro pits decreased and the surface integrity increased with increasing coverage layers.In 0.08 mm particle-water mixture,the mass losses of the three specimens were 14.66 mg,13.54 mg and 12.58 mg.The damaged morphologies of the three specimens in 0.08 mm particle-water mixture were more serious than that in 0.02 mm particle-water mixture.The island structure appeared and the length of CSE cracks decreased with increasing coverage layers.The improvement of microhardness after LSP was beneficial to resisting erosion wear and plastic deformation.Although the residual compressive stress layer cannot reduce the amplitude of stress intensity factor of the crack tip,it can delay the crack growth rate.