Showing papers on "Peening published in 2023"

Microstructure and residual stress modulation of 7075 aluminum alloy for improving fatigue performance by laser shock peening

Abstract: Laser shock peening (LSP) is an advanced surface-strengthening technology that improves the anti-fatigue performance of metallic components. However, there is a significant barrier to the application of thin-walled components because the high-energy laser causes deformation and nonuniformity of compressive residual stress, thereby reducing fatigue performance. In this study, an LSP technology based on a low-pulse-energy laser was developed. We applied it to a thin-walled AA7075 aluminium alloy specimen (∼4 mm thickness) and achieved an improvement in the high-cycle fatigue limit of 20.4 and 37.0% for the smooth and pre-cracked fatigue specimens, respectively, in the absence of deformation. It was discovered that the enhanced dynamic nanoscale precipitation and dislocation multiplication effects of the high-pressure shock wave contribute to microstructure stability under cyclic loading, resulting in high compressive residual stress stability. Moreover, the unique heterogeneous grain structure on the surface layer subjected to LSP at low pulse energy effectively restrains crack initiation and propagation. Because these findings apply to a wide range of alloys, the current results create new avenues for improving the fatigue performance of thin-walled components.

Effects of Shot penning on Mechanical properties, Microstructural Evolution and Residual Stress of Submerged Friction Stir Welded AA6061-T6 Alloy

Abstract: The purpose of this work is to study the effect of shot peening on the mechanical characteristics of welded plates which were performed by Submerged Friction Stir Welding (SFSW) on AA6061-T6 alloy. SFSW was carried out under three cooling mediums like water, brine solution, and coolant oil at the rotational speed of 1200[Formula: see text]rpm and welding speed of 45[Formula: see text]mm/min, respectively. The welded samples from each cooling medium were subjected to a shot peening process. A tensile test was carried out on weld peened and welds unpeened joints. The hardness of the various zones of HAZ, TMAZ, and NZ was also investigated. Optical and scanning electron microscopy was used to examine the microstructures of peened and unpeened joints formed by coolant samples. Shot peening has the potential to enhance the compressive residual stress of friction stir welded joints. According to these findings, shot peening had a greater impact on the mechanical properties of welded samples than unpeened samples, including tensile strength, percentage of elongation, and hardness. The grain size was a little bit smaller than the FSW sample because the surface of the welded samples was subjected to more strain during shot peening.

Microstructure evolution and fatigue properties subjected to optimized coverage areas of laser shock peened TB10 titanium alloy

Abstract: • Nanocrystallization on the TB10 alloy surface was achieved by LSP treatment. • LSP induced hardened layer and compressive residual stress. • The compressive residual stress field perpendicular to the direction of crack propagation improved the fatigue life most significantly. Laser shock peening (LSP) is an advanced surface modification technology, which can induce the high-strain-rate plastic deformation on the metal surface to improve mechanical properties. In this work, the effects of LSP on the microstructure, microhardness, residual stress and fatigue crack growth (FCG) properties of TB10 titanium alloy were investigated. The results showed that LSP could induce high density dislocations and realize the nanocrystallization on the titanium alloy surface. The magnitudes of compressive residual stress and microhardness increased with increasing LSP energy and impact times. The fatigue test showed that the LSP coverage area significantly affected the FCG performance, especially the fatigue life increased by 40.2 % when the LSP area was perpendicular to the cracks. This was attributed to the fact that the FCG rate of early cracks was significantly reduced by a wider region of the compressive residual stress field perpendicular to the crack direction.

Cavitation erosion resistance enhancement of the surface modified 2024T351 Al alloy by ultrasonic shot peening

Abstract: In this study, a novel surface strengthening method for improving cavitation erosion resistance by ultrasonic shot peening (USP) was proposed. Modified 2024T351 aluminium alloy surface layer with the characteristics of refined grains size, increased microhardness and residual compressive stress was prepared by USP treatment. Then the ultrasonic cavitation erosion (UCE) behaviour of the processed 2024T351 Al alloy was investigated. Results indicated that under the combined action of surface hardening and residual compressive stress, the cavitation weight loss of the USP-ed sample was significantly reduced. For the USP-ed 2024T351 Al alloy with an intensity of 0.101mmA, the weight loss after 3 hours' UCE treatment was reduced by 54.2 % compared to the untreated sample. This study also found that the increased surface roughness during shot peening could reduce the cavitation resistance properties. However, the weakening can be avoided by surface finishing. Results indicate that USP is a potential physical strengthening method that can significantly improve the cavitation erosion resistance of metals.

Superior effects of hybrid laser shock peening and ultrasonic nanocrystalline surface modification on fatigue behavior of additive manufactured AlSi10Mg

Abstract: The surface texture of metallic parts produced by laser powder bed fusion (L-PBF) in the as-built condition detrimentally affects their mechanical properties, especially fatigue behavior. Accordingly, applying surface post-treatments has become an attractive approach to improve the mechanical performance of these materials. In the present study, both the individual and combined effects of post-processing methods, i.e., laser shock peening (LSP) and ultrasonic nanocrystalline surface modification (UNSM) with the same intensity of 10–12 A [0.001 in.], were systematically investigated on mechanical properties and fatigue behavior of L-PBF AlSi10Mg specimens. A wide range of experiments involving microstructural characterization, hardness and residual stresses measurements, porosity and surface texture analyses, tensile tests, and rotating bending fatigue tests were conducted. The results revealed that the hybrid LSP + UNSM process resulted in significant improvement in mechanical properties and fatigue behavior due to (i) sub-surface pores closure up to the depth of 517 μm, (ii) 60 % surface hardness improvement, (iii) inducing −420 MPa surface compressive residual stresses, and (iv) surface roughness reduction up to 70 %. The fatigue life was improved up to 75, 56, and 35-fold compared to the as-built state after applying LSP + UNSM, UNSM, and LSP treatments, respectively.

Assessing the efficacy of several impact-based mechanical techniques on fatigue behavior of additive manufactured AlSi10Mg

Abstract: Post-processing methods to reduce issues associated with the presence of internal and external anomalies are often necessary for obtaining adequate structural performance for additively manufactured products. However, the choice of the proper post-treatment and the corresponding parameters is still a challenge requiring adaption to the material type, geometry, size and undeniably costs. In this study, four different pure impact-based mechanical operations involving ultrasonic nanocrystal surface modification (UNSM), ultrasonic shot peening (USSP), severe shot peening (SSP), and severe vibratory peening (SVP) to investigate their efficacy on the fatigue behavior of hourglass AlSi10Mg specimens manufactured via laser powder bed fusion (LPBF) were considered. Experimental characterizations involving microstructural approach, porosity level and surface texture, hardness and residual stresses measurements, as well as tensile and fatigue testing, were conducted. The results exhibited considerable improvement in mechanical/physical performances leading to substantially enhanced fatigue performance of the mechanically treated specimens. Based on a cost-performance analysis, it was found that UNSM, while having reasonable cost, presented considerable improvement on fatigue behavior.

Enhanced strength and sliding wear properties of gas nitrided Ti-6Al-4V alloy by ultrasonic shot peening pretreatment

Abstract: A novel ultrasonic shot peening (USP) was performed on Ti-6Al-4V alloy as a pretreatment prior to gas nitriding (GN). The samples treated by USP/GN composite processes were systematically investigated in terms of microstructure, strength and sliding wear properties. The results indicated that a surface nitriding layer composed of TiN, Ti2N and α-Ti(N) phases with a thickness of 20–30 μm was formed on the samples after USP/GN composite process treatment. The USP pretreatment could significantly improve the microhardness and thickness of nitriding layer, and the enhancement is positively correlated with the intensity of USP Almen. Compared with conventional GN without pretreatment, the maximum microhardness (∼810HV0.025) and thickness of nitriding layer were increased by 30.43 % and 26.92 % by USP/GN composite treatment with Almen intensity of 0.356 mmA, respectively. Meanwhile, the wear resistance was significantly enhanced, and the width of abrasive mark was reduced by 51 %, compared with that without pretreatment. This work offers a potential approach to improve the nitriding process of Titanium alloys.

The influence of laser shock peening on corrosion-fatigue behaviour of wire arc additively manufactured components

Abstract: The need for increased manufacturing efficiency of large engineering structures has led to development of wire arc additive manufacturing (WAAM), which is also known as direct energy deposition (DED) method. One of the main barriers for rapid adoption of the WAAM technology in wider range of industrial applications is the lack of sufficient performance data on the WAAM components for various materials and operational conditions. The present study addresses this essential need by exploring the effects of laser shock peening surface treatment on corrosion-fatigue crack growth (CFCG) life enhancement of WAAM components made of ER70S-6 and ER100S-1 steel wires. The experimental results obtained from this study were compared with the CFCG trends from nominally identical specimens without surface treatment and prove the efficiency of the examined surface treatment method for corrosion-fatigue life enhancement and crack growth retardation of WAAM built steel components, regardless of the material type and specimen orientation. Furthermore, the residual stresses in the WAAM built specimens with and without surface treatment were measured to validate the influence of beneficial residual stresses, arising from surface treatment, on subsequent CFCG behaviour of the material. The residual stress profiles show the beneficial compressive stress fields in the surface treated areas which result in CFCG life enhancement. The results from this study make significant contribution to knowledge by evaluating the suitability of WAAM built steel components for application in offshore environments.

Effects of constrained groove pressing and temperature-assisted ultrasonic shot peening on microstructure and mechanical properties of a two-phase Mg-Li alloy

Abstract: Two passes of constrained groove pressing (CGP) were conducted on a two-phase Mg–Li alloy followed by temperature-assisted ultrasonic shot peening (TA-USP) with different peening durations and temperatures. The effects of TA-USP and CGP on microstructural evolution and mechanical properties were investigated in details. Surface gradient microstructure including nanocrystalline and partial amorphization is introduced by TA-USP. Grain refinement is more significant with longer durations and lower temperatures. Pretreatment by CGP before TA-USP introduces fine and homogeneous microstructure in the alloy due to severe plastic deformation. The average grain sizes of α-Mg and β-Li are refined from the as-annealed 31.6 μm and 12.9 μm to 2.5 μm and 2.2 μm, respectively. The depth of USP-affected region increases with the increase of peening duration and temperature, and a depth of about 300 μm is achieved by direct TA-USP at room temperature with 400 s. The microstructure gradient is reduced at elevated temperatures. The hardness and strength increase while the ductility decreases with the increase of peening duration. The decrease in hardness with the increase of peening temperature is more significant than peening duration. Compared with direct TA-USP, pretreatment by CGP before TA-USP can obviously enhance the surface strengthening. When processed by TA-USP at 200 °C with 100 s, the tensile strength and yield strength increase from 141.9 MPa and 106.2 MPa to 158.3 MPa and 134.7 MPa, respectively. The elongation to failure decreases from 29.1% to an acceptable value of about 16.1%.

Microstructural response and surface mechanical properties of TC6 titanium alloy subjected to laser peening with different laser energy

Abstract: • Laser peening (LP) can induce high amplitude compressive residual stresses. • LP can induce the generation of mechanical twins, dislocations and staking faults. • Microstructural evolution and compressive residual stress improved the friction and wear resistance of TC6 titanium alloy. In this paper, the main purpose was to investigate the effects of laser peening (LP) on the microstructural evolution and frictional wear resistance of TC6 titanium alloy. The surface topographic features, microhardness and residual stress distribution in the depth direction of differently treated specimens were measured using three-dimensional topography instrument, digital microhardness tester and residual stress instrument. The frictional wear test was carried out using a multifunctional friction wear tester. Meanwhile, X-ray diffraction (XRD), optical microscope (OM) and transmission electron microscopy (TEM) were utilized to investigate the effects of LP on the microstructural response of TC6 titanium alloy. The results indicated that the micro-pits induced by LP increased the surface roughness to a maximum of 6.94 μm. LP technique effectively improved the microhardness and frictional wear resistance of TC6 titanium alloy, and the wear form changed from abrasive wear, adhesive wear and fatigue spalling wear to abrasive wear at the laser energy of 8 J. Compared to the untreated specimens, the surface microhardness of the specimens treated by LP with 8 J increased from 356 HV to 442 HV, and the affected layer depth was approximately 500 μm. Moreover, the friction coefficient decreased from 1.2 to 0.5, the abrasion depth of the abrasion track was reduced by approximately 32 % compared to the untreated specimen. Additionally, the surface compressive residual stress induced by LP with 8 J reached about −510 MPa. The microstructural evolution of the specimens processed by LP was dominated by twin formation and dislocation slip, while the intercalation between multidirectional twins and the formation of sub-grain boundaries promoted grain refinement of TC6 titanium alloy. Refined grains, high density of dislocations, mechanical twins and the implantation of compressive residual stresses effectively improved the friction and wear resistance of TC6 titanium alloy.

Effects of Micro-Shot Peening on the Fatigue Strength of Anodized 7075-T6 Alloy

Abstract: Micro-shot peening under two Almen intensities was performed to increase the fatigue endurance limit of anodized AA 7075 alloy in T6 condition. Compressive residual stress (CRS) and a nano-grained structure were present in the outermost as-peened layer. Microcracks in the anodized layer obviously abbreviated the fatigue strength/life of the substrate. The endurance limit of the anodized AA 7075 was lowered to less than 200 MPa. By contrast, micro-shot peening increased the endurance limit of the anodized AA 7075 to above that of the substrate (about 300 MPa). Without anodization, the fatigue strength of the high peened (HP) specimen fluctuated; this was the result of high surface roughness of the specimen, as compared to that of the low peened (LP) one. Pickling before anodizing was found to erode the outermost peened layer, which caused a decrease in the positive effect of peening. After anodization, the HP sample had a greater fatigue strength/endurance limit than that of the LP one. The fracture appearance of an anodized fatigued sample showed an observable ring of brittle fracture. Fatigue cracks present in the brittle coating propagated directly into the substrate, significantly damaging the fatigue performance of the anodized sample. The CRS and the nano-grained structure beneath the anodized layer accounted for a noticeable increase in resistance to fatigue failure of the anodized micro-shot peened specimen.

Improvement of strength-ductility synergy of Mg–Al–Mn alloy using laser shock peening-induced gradient nanostructure

Abstract: The trade-off between strength and ductility of magnesium alloy is a general bottleneck. Herein, we presented a method, laser shock peening (LSP), to overcome this problem. The key is the preparation of plastic strain-induced gradient nanostructure along the depth direction. Gradient nanostructure has unique deformation mechanism in the process of tensile deformation. Due to the cooperative effects of deformation twinning, dislocation movement, and dynamic recrystallization, the gradient nanostructured AM50 magnesium alloy contributed to ∼12% improvement of ultimate tensile strength, while ∼3% reduction of tensile ductility. Furthermore, the formation mechanisms of LSP-induced gradient nanostructure at initial plastic deformation stage, severe plastic deformation stage, and surface nanocrystalline stage were explored.

State of the Art and Perspectives on Surface-Strengthening Process and Associated Mechanisms by Shot Peening

Abstract: Shot peening is a surface-strengthening process that is widely used in various industries, such as aerospace, automotive, and biomedical engineering. The process involves the impact of small, spherical media, called shots, onto the surface of a material, resulting in residual compressive stress and improved surface properties. This review aims to provide an overview of the state of the art and perspectives on surface strengthening by shot peening. The review covers various aspects of shot peening, including process parameters, shot materials, and quality control techniques. The advantages and limitations of shot peening in comparison to other surface-strengthening techniques are also discussed. The findings of this review indicate that shot peening is a versatile and effective surface-strengthening technique with numerous applications, and further research is needed to fully realize its potential. In conclusion, this review provides insights into the current status and future perspectives on surface strengthening by shot peening, and it is expected to be useful for researchers, engineers, and practitioners in the field of material science and engineering.

A Critical Review of Laser Shock Peening of Aircraft Engine Components

Abstract: Many aviation accidents have been caused by the failure of aircraft engine components, and engine blades are especially vulnerable to high-cycle fatigue fracture in severe working environments as well as to impact damage caused by foreign objects. To address this problem, the United States took the lead and has been successful in implementing laser shock peening (LSP) as a surface treatment for aircraft engine components to enhance their fatigue performance. This review provides an overview of the development of LSP for use in treating aircraft engine components over the past three decades, with a brief introduction to the development of high-energy pulsed lasers for LSP. A particular focus of this review is on the limitations and challenges associated with the application of LSP for treating critical aircraft engine components. It is hoped that this review will serve as a reference for future research and development that can lead to better performance of these components. This article is protected by copyright. All rights reserved.

Effect of Laser Peening on the Corrosion Properties of 304L Stainless Steel

Abstract: Dry canisters used in nuclear power plants can be subject to localized corrosion, including stress corrosion cracking. External and residual tensile stress can facilitate the occurrence of stress corrosion cracking. Residual stress can arise from welding and plastic deformation. Mitigation methods of residual stress depend upon the energy used and include laser peening, ultrasonic peening, ultrasonic nanocrystal surface modification, shot peening, or water jet peening. Among these, laser peening technology irradiates a continuous laser beam on the surface of metals and alloys at short intervals to add compressive residual stress as a shock wave is caused. This research studied the effect of laser peening with/without a thin aluminum layer on the corrosion properties of welded 304L stainless steel. The intergranular corrosion rate of the laser-peened specimen was a little faster than the rate of the non-peened specimen. However, laser peening enhanced the polarization properties of the cross-section of 304L stainless steel, while the properties of the surface were reduced by laser peening. This behavior was discussed on the basis of the microstructure and residual stress.

Tribological, Corrosion, and Microstructural Features of Laser-Shock-Peened Steels

Abstract: The degradation due to high friction, wear, and corrosion of mechanical components for industrial applications has invoked substantial economic loss. In recent years, scientists and engineers have developed techniques to mitigate the issues associated with this deterioration potentially. Among these developed techniques, controlling the coefficient of friction (COF), wear rate, and corrosion using laser shock peening (LSP) is a preeminent and popular innovation. This paper aims to summarize the existing literature on the LSP of steels, discuss the current state-of-the-art LSP, and demonstrate the mechanisms that dictate the enhanced tribological and corrosion properties. More specifically, the influence of LSP on COF, wear rate, corrosion potential, surface hardening, and surface morphological changes on various materials used for aerospace, automotive, biomedical, nuclear, and chemical applications is explained. In addition, grain refinement and the gradient microstructure formation during LSP are discussed. Additionally, recent advances and applications of LSP are elucidated.

Surface Layer Strengthening Mechanism of 2060 Aluminum-Lithium Alloy after Shot-Peening

Abstract: The microstructure evolution and strengthening mechanism of materials after shot peening have always been the focus of research. In this paper, a novel coupled constitutive model was proposed to predict the depth of fine-grain of the 2060-T8 aluminum-lithium (Al–Li) alloy after shot peening. Besides, combining the numerical and experimental methods, the influences of shot size on yield stress, dislocation density, and crystal orientation of Al–Li alloy were systematically studied to reveal the strengthening mechanism. The results show that larger shot sizes can significantly improve the depth of the dislocation density layer and the fine-grain layer of 2060 Al–Li alloy. The depth of the refinement layer increases from 50 μm to 80 μm when the shot size grows from 0.3 mm to 0.6 mm. It is found the depth of the grain refinement layer in the experiment is consistent with the depth where is a sudden change of grain size in the simulation. Additionally, electron backscatter diffraction (EBSD) shows that many sub-grains are produced in the material due to high dislocation density, and the proportion of low-angle grain boundaries (LAGB) increases significantly, from 48.3% to more than 98.4%. The crystal orientation in the grain has changed obviously and Goss texture {100}<001> obtained in the deformation band. In contrast, with the increase in shot size, the proportion of the Schmid factor with a high-level trend increases. However, the hardening effect of the material is much greater than the softening effect which results in higher yield stress and microhardness of the top surface.

Effect of multiple laser shock peening without coating on residual stress distribution and high temperature dry sliding wear behaviour of Ti-6Al-4 V alloy

Abstract: The effect of laser peening without coating (LPwC) on the tribological behaviour of Ti-6Al-4 V alloy at ambient (28 °C) and elevated temperatures (300 °C) was investigated. The influence of residual stress, microhardness, microstructure, and surface roughness is discussed. The samples show maximum compressive residual stress of –550 MPa and hardness of 395 HV after peening. Electron back scattered diffraction (EBSD) analysis shows the reduction in average grain size and increase in Low-angle grain boundaries fraction for LPwC samples compared to unpeened samples. The average friction coefficient and wear volume loss were found to be significantly reduced after the laser peening process. At ambient temperature, a severe abrasive wear mechanism was identified in unpeened samples, and a mild abrasive wear mechanism was observed for LPwC samples. LPwC samples show a relatively smooth worn surface than the unpeened samples, resulting in reduced wear volume loss of 30, 24.75 and 17.08 % than the unpeened samples at 10, 20 and 30 N loading conditions. At elevated temperature, unpeened samples show severe abrasive wear and mild oxidative wear mechanism, whereas, in LPwC samples, the wear mechanism shifted from severe abrasive to oxidative and mild abrasive wear resulting in reduced wear volume loss of 30.3, 19.58 and 13.43 % compared to unpeened samples at 10, 20 and 30 N loading condition respectively.

A study on bending deformation behavior induced by shot peening based on the energy equivalence

Abstract: Shot peening is an essential process for forming large thin-walled components in aerospace industries. However, it is challenging to determine directly the mapping relationship between shot peening parameters and deformation response because of the complex elastic–plastic deformation of shot-peened components. In this paper, a computational model of bending deformation of peened plate samples is established by examining the shot peening behavior from the aspect of energy equivalence, in which the deformation energy of the shot-peened plate is determined by the total kinetic energy input due to the shot impacts and a correction factor that takes into account the influences of oblique impact, shot interaction and shot overlap on the peen forming process in practice. It is proven that the square of curvature radius is proportional to the cube of the thickness but inversely proportional to the indentation coverage and the average kinetic energy input of a single shot. For the effect of a single shot impact in peen forming, the average kinetic energy input of a single shot is a power function with the indentation diameter.