Effect Of Laser Shock Peening On The Microstructure And .
The Author(s)1059-9495/ 19.00JMEPEG (2020) 4667-3Effect of Laser Shock Peening on the Microstructureand Properties of the Inconel 625 Surface LayerMagdalena Rozmus-Górnikowska, Jan Kusiński, and Łukasz Cieniek(Submitted August 19, 2019; in revised form January 21, 2020; published online February 19, 2020)The aim of this work was to investigate the influence of laser shock peening on the topography,microstructure, surface roughness and the mechanical properties of the Inconel 625 nickel alloy. Examination of the topography and microstructure of the nickel alloy after laser treatment was carried out bymeans of scanning electron microscopy as well as atomic force microscopy. The roughness of the surfacewas measured by WYKO NT9300 equipment. Nanohardness test was carried out using a nanoindenterNHT 50-183 of CSM Instruments equipped with a Berkovich diamond indenter. Additionally, transmissionelectron microscopy was used to examine the microstructural changes on the surface layer after lasertreatment. The investigations showed that the laser process produced an ablation and melting of the surfacelayer and, hence, increased the surface roughness of the Inconel 625. On the other hand, the presence of theslip bands on the surface and on the cross section of the treated material, a high density of dislocations anda higher hardness of the treated region indicated that the laser shock processing caused severe plasticdeformation of the surface layer. Additionally, due to the high plastic deformation, cracking of the carbideprecipitates was observed.KeywordsInconel 625, laser shock peening (LSP),microstructure, nanohardness, surface roughness1. IntroductionLaser shock peening (LSP) also known as laser shockprocessing is an innovative laser-based surface processingtechnique used to modify the surface of a metallic material,which causes compressive residual stresses and microstructuralchanges on the surface and within the depth of the metal (Ref 14). Often, LSP is used to treat many aerospace products, such asturbine blades, rotor components, disks, gear shafts and bearingcomponents (Ref 5, 6).In the LSP process, a laser beam hits the sacrificial coatingon the surface of the metallic target and forms plasma, whichrapidly expands and generates shock waves into the bulk (Ref7, 8). These shock waves induce compressive residual stressesinto the metal and improve its fatigue life, which is veryimportant in applications such as turbine blades of aircraftengines. When the induced compressive residual stresses reachthe yield strength of the treated metal, plastic deformationoccurs.This article is an invited submission to JMEP selected frompresentations at The XXII Physical Metallurgy and Materials ScienceConference: Advanced Materials and Technologies (AMT 2019) heldJune 9-12, 2019, in Bukowina Tatrzańska, Poland, and has beenexpanded from the original ński,andŁukasz Cieniek, Faculty of Metals Engineering and IndustrialComputer Science, AGH University of Science and Technology, al.Mickiewicza 30, 30-059 Kraków, Poland. Contact e-mail:rozmus@agh.edu.pl.1544—Volume 29(3) March 2020The main advantages of the LSP process are a greaterresidual compressive stress depth when compared to traditionalmechanical shot peening and more flexibility in process controlparameters. Furthermore, it is possible to apply LSP to onlyselected regions of a component, because of the ability toprecisely control the position of the laser (Ref 9, 10). In theaerospace industry, LSP is an effective method to improve themechanical properties and fatigue lives of key aerospaceproducts, such as turbine blades and rotor components (Ref 11).Nickel-based superalloys have excellent mechanical properties, especially at medium and high temperatures (Ref 12, 13).These properties make nickel alloys widely used in aero-engineapplications, such as turbine disks and blades. Therefore, manyresearchers e treated material. SEM imagesshow that cracks appear in carbides on the extension of the slipbands, as indicated by the arrows in Fig. 4.According to literature data (Ref 2, 8), in metallic materialssuch as steel, aluminum or titanium alloys with relatively goodductility and fracture toughness, LSP process has beensuccessfully used to improve fatigue, wear and stress corrosioncracking resistance. However, in brittle materials such as oxidesor carbides, LSP has not been widely used, and the effect of thisprocess on these materials is still poorly understood. Zhanget al. (Ref 9, 20) investigated laser shocking of Al2O3 ceramicsand further studied the fracture morphology that formed fromthe strong laser shock processing. It was found that brittlefracture occurred at a laser pulse energy of 42 J. When the laser1546—Volume 29(3) March 2020Journal of Materials Engineering and Performance
Fig. 6 TEM bright-field image (a) showing microstructure of the Inconel 625 after LSP process (TEM) as well as the corresponding diffractionpattern (b)Fig. 7Nanohardness of the treated sample as a function of a depthenergy was reduced to 25 J, the brittle fracture of ceramicsappears to be comprised of plastic deformation (Ref 9, 20).Probably, cracking of carbides in the investigated materialoccurs due to large plastic deformation, but one shouldremember that the consequence of the cracking of carbidesmay be the concentration of high compressive stress levels intheir vicinity.The surface roughness of the material was measured forboth the untreated and the laser-shock-peened nickel alloys.The average roughness Ra (arithmetic average of the absolutevalues of the profile height deviations from the mean line)increased from 100 nm before treatment to 1 lm after LSPprocess. Figure 5 shows the 3D optical surface profile imagesof the untreated (a) and treated (b) samples. It is evident [andconsistent with the literature (Ref 4, 5)] that the LSP treatmentincreases the roughness of the surface. The increase in surfaceroughness is a consequence of the combined effect of the laserpulse pressure and the ablative nature of the laser process.Typical TEM images of the near-surface microstructure ofthe specimen treated by LSP are shown in Fig. 6(a) and (b).The dense slip bands (Fig. 6a) formed under the dynamicJournal of Materials Engineering and Performanceconditions characteristic to LSP indicate that the formation ofslip bands is easier under high-strain-rate conditions, whichshow qualitative agreement with cross-slip simulations made byWang et al. (Ref 21). Figure 6(b) shows a fractured carbideparticle (arrowed) stopping the crossing slip bands at an angleof 60 . It seems that the plastic deformation level reached athreshold value, fracturing the marked carbide. The crossingslip bands associated with precipitate shearing would beexpected to give rise to crack initiation.The TEM micrographs reveal a remarkably high density ofdislocations. Similar observations were made by other investigators (Ref 16, 22-25). Ren et al. (Ref 22) noted that LSPgenerated high-density dislocations and improved the mechanical properties of aluminum alloys. Yan et al. (Ref 25) indicatedthat a high density of dislocations, stacking faults anddeformations twins were generated in oxide dispersionstrengthened austenitic steels after LSP.The nanohardness values of the Inconel 625 measured onthe polished cross sections without LSP treatment wereapproximately 270 HV. After the LSP process, the nanohardness measured near the surface increased to a value 350 HV. AVolume 29(3) March 2020—1547
40% increase in hardness is associated with the high density ofdislocations generated in the surface region in the irradiatedspot during the LSP process as well as a high density of slipbands. The graph illustrating the variation of the nanohardnessof the sample as a function of a depth is presented in Fig. 7. Asthe depth exceeds 80 lm, the nanohardness tends to beconstant. A similar trend that hardness increases after theLSP process was also observed in previous reports on variousalloys after laser shock peening (Ref 26).4. ConclusionsIn this paper, the linkage between microstructure, deformation mode and hardness has been examined and discussed. Inall cases examined, the deformation is localized within a ratherlarge number of deformation bands. The following conclusionscan be drawn from this study: The laser shock processing produced melting and ablationof the surface layer of the treated material; however, thepresence of dense slip bands on the surface and on thecross section of the treated material as well as a high density of dislocations indicated that severe plastic deformation appears in the surface layer of investigated materialafter LSP process.Due to the plastic deformation, cracking of carbides bycrossing slip bands associated with precipitate shearingwas observed.The surface of the treated material was roughened by theLSP process.The values of nanohardness in the laser-shocked regionwere clearly higher than those in the non-shocked region.The enhancement of LSP on the nanohardness of Inconel625 nickel alloy was mainly due to the high density ofslip bands and dislocations.Below the surface, the shock hardening effect decreaseswith increasing distance from the surface.AcknowledgmentsThe investigations were financed by the AGH University ofScience and Technology Project 16.16.110.663 – zad.1.Open AccessThis article is licensed under a Creative Commons Attribution 4.0International License, which permits use, sharing, adaptation,distribution and reproduction in any medium or format, as long asyou give appropriate credit to the original author(s) and the source,provide a link to the Creative Commons licence, and indicate ifchanges were made. The images or other third party material in thisarticle are included in the article’s Creative Commons licence,unless indicated otherwise in a credit line to the material. Ifmaterial is not included in the article’s Creative Commons licenceand your intended use is not permitted by statutory regulation orexceeds the permitted use, you will need to obtain permissiondirectly from the copyright holder. To view a copy of this licence,visit �Volume 29(3) March 2020References1. A. Telang, Ch. Ye, A. Gill, S. Teysseyre, S.R. Mannava, D. Qian, andV. K. Vasudevan, Effect of Laser Shock Peening on SCC behavior ofalloy 600, in 16th International Conference on EnvironmentalDegradation of Materials in Nuclear Power System-Water Reactors,2013, Idaho National Laboratory2. M. Rozmus-Górnikowska, J. Kusiński, and M. Blicharski, Laser ShockProcessing of an Austenitic Stainless Steel, Arch. Metall. Mater., 2010,55(3), p 635–6393. X. Yi, H. Tian-tian, L. Peng-yan, C. Lu-fei, R. Feng-zhang, and A.A.Volinsky, Effect of Laser Pulse Energy on Surface Microstructure andMechanical Properties of High Carbon Steel, J. Cent. South Univ.,2015, 22, p 4515–4520. https://doi.org/10.1007/s11771-015-3000-14. M. Rozmus-Górnikowska, J. Kusiński, and M. Blicharski, TheInfluence of the Laser Treatment on Microstructure of the SurfaceLayer of an X5CrNi18-10 Austenitic Stainless Steel, Arch. Metall.Mater., 2011, 56(3), p 717–721. https://doi.org/10.2478/v10172-0110079-85. A.S. Gilla, A. Telang, and V.K. Vasudevan, Characteristics of SurfaceLayers Formed on Inconel 718 by Laser Shock Peening With andWithout a Protective Coating, J. Mater. Process. Technol., 2015, 225,p 463–472. 24-01366. R. Sundar, B.K. Pant, H. Kumar, P. Ganesh, D.C. Nagpure, P. Haedoo,R. Kaul, K. Ranganathan, K.S. Bindra, S.M. Oak, and L.M. Kukreja,Laser Shock Peening of Steam Turbine Blades for Enhanced ServiceLife, Pramana J. Phys., 2014, 82(2
Keywords Inconel 625, laser shock peening (LSP), microstructure, nanohardness, surface roughness 1. Introduction Laser shock peening (LSP) also known as laser shock processing is an innovative laser-based surface processing technique used to modify the surface of a metallic material, which causes compressive residual stresses and microstructural
Fig. 1 & 2: laser peening (left) and shot peening (right) basic concepts 1-Effects of Laser Peening and Shot Peening on material The effects of laser peening and shot peening on the processed material can be grouped in three categories: Redistribution of residual stresses Surface topography modification Cold work 1-1 Residual stress
Shock wave Fig.1 Schematic of laser peening Fig. 2 Comparison of residual stress profiles in each condition Table2 Laser peening parameters the compressive residual stress layer built by laser peening is deeper than that of shot peening(3). (2) Material Some aluminum forgings have been used in numerous fatigue critical parts of aircrafts with
development of high peak power short pulse from Nd:YAG laser along with its peening application. It presented the design scheme of laser and the characteristic of laser beam transmission. Zhu [15] et al. discussed the influence of laser shock peening on surface morphology and mechanical property of Zr-based bulk metallic glass.
Laser Shock Peening (air) An extension of conventional peening Laser peening provides – Highly compressive surface residual stress – Deep layer of compressive residual stress – Smooth surface – Excellent process control Laser near field image Laser peened aluminum
Laser shock peening LSP method has potential to improve the mechanical properties of Cu-Ni alloys, the present study has been done to basically understand the effects of laser shock peening of LSP on the deformation microstructure, hardness, residual stress, and in this Monel K 400 specimen.
13 samples before and after laser shock peening. The porosity in two additively manufactured aluminum 14 alloy (AlSi10Mg) tensile samples before and after laser shock peening was imaged using identical X-ray 15 tomography settings and overlap of the data was performed for direct comparison. The results indicate
effects was investigated. We adopted a laser peening meth-od that can be used to treat metals without a protective coating [9, 10], which can induce a compressive residual stress in metals by increasing the coverage. In the estimation of the effects of laser peening i.e., the performance of laser peening, magnitude of compres-
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