Effect of Laser Shock Peening on the Microstructure and Properties of the Inconel 625 Surface Layer

The paper presents the results of experimental studies on the impact of impulse shot peening parameters on surface roughness (Sa, Sz, Sp, Sv), surface layer microhardness, and the mean positron lifetime (τmean). In the study, samples made of the Inconel 718 nickel alloy were subjected to impulse shot peening on an originally designed stand. The variable factors of the experiment included the impact energy, the diameter of the peening element, and the number of impacts per unit area. The impulse shot peening resulted in changes in the surface structure and an increase in surface layer microhardness. After the application of impulse shot peening, the analyzed roughness parameters increased in relation to post-milling values. An increase in microhardness was obtained, i.e., from 27 HV 0.05 to 108 HV 0.05 at the surface, while the maximum increase the microhardness occur at the depth from 0.04 mm to 0.08 mm. The changes in the physical properties of the surface layer were accompanied by an increase in the mean positron lifetime τmean. This is probably related to the increased positron annihilation in point defects. In the case of small surface deformations, the increase in microhardness was accompanied by a much lower increase in τmean, which may indicate a different course of changes in the defect structure consisting mainly in modification of the dislocation system. The dependent variables were subjected to ANOVA analysis of variance (it was one-factor analysis), and the effect of independent variables was evaluated using post-hoc tests (Tukey test).

“…Shot peening increases the fatigue strength of elements made of nickel alloys working at elevated temperatures [ 20 ]. Nickel alloys are treated with laser shot peening as well [ 21 ].…”

Section: Introductionmentioning

confidence: 99%

Analysis of Surface Properties of Nickel Alloy Elements Exposed to Impulse Shot Peening with the Use of Positron Annihilation

Skoczylas

Zaleski

et al. 2021

“…Laser peening is the cold forming process used to treat the surface, and compressive residual stress can be achieved by the shock wave due to the expansion of high-pressure plasma. In the laser peening process, a focused, high-energy, and short-pulsed laser beam irradiates the surface of a metal specimen, which is usually covered with a thin layer of overlay water [ 27 ], glass [ 28 ], paint [ 29 ], aluminum foil [ 30 , 31 ], or tape [ 32 , 33 ] for protection against melting [ 28 ].…”

Section: Introductionmentioning

confidence: 99%

Effect of Laser Peening on Microstructural Changes in GTA-Welded 304L Stainless Steel

Yoo

Kim

2022

The introduction of tensile residual stress has led to the induction of damage such as fatigue, corrosion fatigue, and stress corrosion cracking (SCC) in stainless steel in association with the influence of environments, components, surface defects, and corrosive factors during its use. Compressive residual stress can be achieved through various techniques. Among several methods, laser peening can be more attractive as it creates regularity on the surface with a high-quality surface finish. However, there is very little research on heavily peened surface and cross-section of stainless steel with very deep compressive residual stress. This work focused on welding and laser peening and the influence of Al coating on the microstructural changes in 304L stainless steel. The specimen obtained by laser peening had a very deep compressive residual stress of over 1 mm and was evaluated based on microstructural and hardness analysis. Therefore, a model for microstructural change by laser peening on welded 304L stainless steel was proposed.

“…LSP generates microstructure modification, including grain size reduction [ 17 , 18 ], dislocation proliferation and rearrangement [ 19 , 20 , 21 ] and mechanical twin generation [ 22 ]. Górnikowska et al [ 23 ] investigated the influence of LSP on the topography, microstructure, surface roughness and the mechanical properties of the Inconel 625 nickel alloy. It was concluded that the LSP caused severe plastic deformation of the surface layer, resulting in the slip bands on the surface and cross-section of the treated material, a high density of dislocations and a higher hardness of the treated region.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Strain Fatigue Behavior for Inconel 625 with Laser Shock Peening

Sun

Han

et al. 2022

With excellent creep resistance, high-temperature thermal strength and high-temperature fatigue strength, Inconel 625 is widely applied to fabricate structural components in the aerospace field, where fatigue life is a key point. Laser shock peening (LSP) is considered to improve the fatigue strength and fatigue crack growth resistance of metal materials. The present work was conducted to investigate the influence of LSP on strain-controlled fatigue behavior of Inconel 625. The surface microstructures of specimens before and after LSP were observed by transmission electron microscope (TEM). The strain-controlled fatigue loading tests with different strain amplitudes ranging from 0.4% to 1.2% were carried out on the specimens, and the topography of fracture appearance was examined by scanning electron microscope (SEM). The investigations showed that the specimens with LSP presented fewer crack initiations, shorter fatigue striations space and smaller dimples or micropores, which account for the enhancement of the fatigue life for the LSP specimens. Furthermore, the plastic deformation, ultra-fine grains, twins and dislocations caused by LSP could prevent crack initiation, crack propagation and ultimate fracture, hence prolonging the fatigue life of the Inconel 625. In addition, it was revealed that the cyclic strain hardening as well as cyclic strain softening remains almost the same to Inconel 625 with or without LSP.