Showing papers on "Peening published in 2019"

Laser Shock Peening, the Path to Production

Abstract: This article describes the path to commercialization for laser shock peening beginning with the discovery of the basic phenomenology of the process through to its implementation as a commercial process. It describes the circumstances leading to its invention, the years spent on exploring and defining characteristics of the process, and the journey to commercialization. Like many budding technologies displaying unique characteristics, but no immediately evident application, i.e., “a solution looking for a problem”, there were several instances where its development may have been delayed or ended except for an unanticipated event that enabled it to move forward. An important contributor to the success of laser peening, is that nearly 15 years after its invention, universities world-wide began extensive research into the process, dramatically broadening the knowledge base and increasing confidence in, and understanding of its potential. Finally, a critical problem in need of a solution, laser peening, appeared, culminating in its first industrial application on aircraft turbine engine fan blades.

The effect of surface plastic deformation produced by shot peening on corrosion behavior of a low-alloy steel

Abstract: Shot peening treatment is a well-known and practical method to improve surface properties of materials. In this method, surfaces of materials are peened by small steel shots and thus, surface hardening is provided. Although it is used in a wide range of applications, this process could affect the electrochemical behavior of materials because of changing surface properties. Therefore, the effects of shot peening process on the electrochemical properties of a low-alloy steel were examined in the present study. AISI 4140 low-alloy steel samples were shot peened in different intensities of 16 A, 18 A, 20 A and 24 A. Afterwards, corrosion tests were carried out at room temperature in a 3.5% NaCl solution. Open circuit potential (OCP) electrochemical polarization and electrochemical impedance spectroscopy (EIS) analysis were performed in corrosion tests. The microstructural, morphological and surface properties of samples were analyzed by XRD, SEM and 3D surface profilometer. The structural analyses showed that grain structure of the material was affected by shot peening treatment. A plastically deformed zone, which have extended and refined grain structure, formed after shot peening processes. Electrochemical analyses indicated that the corrosion resistance of the material increased with the increasing shot peening intensity owing to grain refinement and formation of sub-grains. Also, examinations on the corroded surfaces showed that crevice corrosion was the main mechanism for shot peened samples.

Healing cracks in selective laser melting by 3D laser shock peening

Abstract: Selective Laser Melting (SLM) of Ni-based superalloys such as CM247LC is prone to weld-cracking. This paper investigates how to suppress cracks by repeatedly applying Laser Shock Peening (LSP) during the building phase of SLM. Samples made of CM247LC were processed with different LSP parameters, and the influence on bulk crack density has been quantified. It was observed that for all chosen conditions, a significant decrease of up to 95% could be achieved, demonstrating the potential of the new hybrid 3D LSP method in improving SLM processability of alloys sensitive to cracking.

Laser Shock Peening and its Applications: A Review

Abstract: In this paper Laser Shock Peening (LSP), as a surface treatment technique for metals and alloys is reviewed. A brief introduction covering LSP process, LSP on various materials and some innovative applications of LSP have been discussed. Critical laser parameters for LSP such as laser energy, pulse width, wavelength, overlap rate, role of sacrificial coating and transparent overlay are presented towards parameter optimization perspective. A small section has been devoted to detail the development of a pulsed Nd:YAG laser that was built in house, exclusively for the LSP applications. Role of LSP in improving the material properties such as fatigue, Stress Corrosion Cracking (SCC), Inter Granular Corrosion (IGC) besides, rejuvenation of fatigue life of pre fatigued specimens and hybrid technique to rejuvenate the SCC damaged components are discussed. Further, results on oblique laser peening along with its successful application to the interior of cylindrical geometry specimens for improving the SCC resistance are also discussed.

Study on the effect of multiple laser shock peening on residual stress and microstructural changes in modified 9Cr-1Mo (P91) steel

Abstract: This paper presents an experimental study on the effect of laser shock peening (LSP) parameters on resultant surface residual stress and microstructural evolution in P91 steel. P91 steel samples were subjected to single and multiple LSP treatments. Single LSP treatment was performed with laser power density (LPD) in the range of 3.9–5.5 GW cm−2 while multiple LSP treatment was carried out a fixed LPD of 3.9 GW cm−2. The surface of laser shock peened samples was investigated with respect to residual stress, microstructure and micro-hardness through X-ray diffraction (XRD), scanning and transmission electron microscopy and micro-hardness measurements. Single LSP treatment produced significant increase in the magnitude of compressive residual surface stress (−570 to −610 MPa) with respect to unpeened sample with compressive surface stress of around ±85 MPa. However with increasing the LPD beyond 3.9 GW cm−2, the compressive residual surface stress has marginally increased. On the other hand, in case of multiple LSP treated samples, the magnitude of compressive residual surface stress has been observed at increased depth of 975 μm (double LSP) and ~1200 μm (triple LSP) compared to single LSP impact (~750 μm). Further, microstructural analysis carried out using electron microscopy of laser peened samples demonstrated that in the near surface region, martensite lath structure under gone severe refinement with respect to the unpeened sample having average lath width ~1.2 μm. It has also been noticed that grain refinement is found be more prominent in the case of multiple LSP treated samples. The grain refinement in LSP treated samples was also confirmed by XRD peak broadening which progressively increases with an increase in laser impacts. Electron microscopic characterization revealed that in triple LSP treated P91 samples, well-defined polygonal subgrains of average size ~115 ± 10 nm have been observed at near surface (20 μm depth from top).

Fatigue life and microstructure of additive manufactured Ti6Al4V after different finishing processes

Abstract: Finishing methods of additive manufactured metal parts are becoming a key driver of industrial viability, increasingly with additive processes being challenged in demanding end-product applications. The same scenario stresses the requirements as to fatigue life of parts built by Additive Manufacturing (AsM). The paper addresses fatigue life of Ti6Al4V produced by Powder Bed Fusion in four finishing conditions: as-built, tool machined, after tumbling and after tumbling and subsequent shot-peening. Failure mechanisms at the micro-scale are observed in order to reinforce the mechanical results by identifying the role of different surface morphologies in crack initiation. X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques and microanalysis (EDX) are used to investigate microstructural modifications generated by the different finishing methods. Results show that tumbling alone does not improve fatigue life against the as built condition, whereas tumbling and subsequent shot peening allow matching the fatigue endurance of tool machined specimens. The shot peening process causes surface amorphization and implantation of the peening media turning into subsurface inclusions. Based on the results, an optimized finishing process can be envisaged, consisting in prolonged tumbling up to the removal of a stock allowance at least equal to the powder size, before shot peening.

Pore Closure Effect of Laser Shock Peening of Additively Manufactured AlSi10Mg

Abstract: This article reports on an exceptional insight provided by nondestructive X-ray tomography of the same samples before and after laser shock peening (LSP). The porosity in two additively ma...

Investigations on the tooth root bending strength and the fatigue fracture characteristics of case-carburized and shot-peened gears of different sizes:

Abstract: This paper contains data of the research project FVA 293 III by Schurer et al. and investigates the tooth root bending strength and the fatigue fracture characteristics of case-carburized and shot-...

Effect of laser shock peening on wear behaviors of TC11 alloy at elevated temperature

Abstract: Titanium alloy is regarded as a high performance material which has wide application prospect in aerospace and medical field. However, their poor wear properties may lead to failures in early service stages. In this paper, the microstructure, micro-hardness and residual stress of TC11 alloy treated by laser shock peening (LSP) are investigated. The sliding wear experiments are performed to study the influence of various temperature and applied load on the wear behaviors of TC11 alloy with and without LSP. The results indicate that the LSPed specimen has a superior wear properties to that of as-received specimen under the same wear test conditions. The tribological properties are greatly dependent on wear testing temperature and applied load. For the specimens tested under 15 N, the variation trend of friction coefficient and wear rate reduces first (25–500 °C) and then increases (500–600 °C) with increasing the test temperature. When the sliding wear test conducted at 400 °C, the larger the applied load, the more the friction coefficient and wear rate. The prominent tribological performances of LSPed TC11 alloy is ascribed to the high compressive residual stress and grain refinement induced by LSP.

Use of an Abrasive Water Cavitating Jet and Peening Process to Improve the Fatigue Strength of Titanium Alloy 6Al-4V Manufactured by the Electron Beam Powder Bed Melting (EBPB) Additive Manufacturing Method

Abstract: Metal components made by additive manufacturing have large inherent surface roughness, and, as such, their strength and fatigue life can be reduced significantly versus wrought products. In order to improve these properties, a novel mechanical surface treatment that introduces compressive residual stress while simultaneously reducing the surface roughness is proposed. The proposed treatment uses cavitation peening combined with an abrasive slurry. The impact of the kinetic energy-charged abrasive particles, induced by collapsing water cavitation vapor bubbles, produces compressive residual stress, while the abrasive reduces the surface roughness. Plane-bending fatigue tests were carried out to determine the effectiveness of this treatment on the fatigue life and strength of titanium alloy Ti6Al4V manufactured by electron beam melting. It was demonstrated that the fatigue strength of an as-built specimen was improved from 169 MPa to 280 MPa by the proposed treatment.

Ultrasonic Peening Treatment Used to Improve Stress Corrosion Resistance of AlSi10Mg Components Fabricated Using Selective Laser Melting

Abstract: As a rapidly evolving advanced digital manufacturing technology, additive manufacturing (AM) has its advantages including short manufacturing cycle, material saving, and complexity for free. It has great potential for application in marine and offshore engineering. However, stress corrosion damage will be a big threat for the additively manufactured metal parts in the ocean environment due to large residual stresses generated in the building process. This paper focuses on the effect of ultrasonic peening treatment (UPT) on stress corrosion resistance of AlSi10Mg components fabricated using Selective Laser Melting (SLM). Firstly, AlSi10Mg specimens were prepared using an SLM machine, and UPT was conducted on the specimen’s top surface. Then, a series of measurements and analyses were carried out for the specimens before and after the UPT process. The residual stresses and hardness of the specimens were measured, and the surface morphology was observed using a scanning electron microscope (SEM). The resistance of stress corrosion was evaluated by the electrochemical corrosion test. The experimental results show that UPT can significantly improve stress corrosion resistance of SLM-fabricated specimens.

Effects of shot peening pre-treatment and plasma nitriding parameters on the structural, mechanical and tribological properties of AISI 4140 low-alloy steel

Abstract: In recent years, hybrid surface treatments which include plasma nitriding combined with pre-shot peening operations have been proposed for the improvement of nitriding efficiency. The main objective of this study is to characterize the effects of dual process on the friction and wear behavior of metallic materials. For this purpose, AISI 4140 steel samples were shot peened at various densities of 16, 20 and 24 A. The pre-treated samples were plasma nitrided at a temperature of 500 °C for 1 and 4 h. The structural and mechanical properties of samples were analyzed by XRD, SEM and microhardness tester. Wear tests were performed under dry sliding conditions to determine the tribological properties of the samples. This study showed that the shot peening treatment formed finer grains, compressive residual stresses on the surface and increased the diffusion kinetics of the samples. The surface hardness and residual stresses increased with increasing shot peening density. It was evidence that the finer grains, increased dislocation density and surface defects increased the case depth obtained from plasma nitriding by enabling easier diffusion of nitrogen. The depth of the diffusion zones in shot peened plus plasma nitrided specimens was found almost two times thicker than that of the diffusion zones in specimens treated only by plasma nitriding. The highest surface hardness values were obtained from pre shot peened and plasma nitrided samples in consequence of the interactive effect from nitride phases/layers and increased surface compressive residual stress. As a result, pre-shot peened plus plasma nitrided samples exhibited higher wear resistance than specimens treated only by shoot peening and hybrid treating in glow a discharge atmosphere.

Effect of laser shock peening on the microstructure and corrosion resistance in the surface of weld nugget zone and heat-affected zone of FSW joints of 7050 Al alloy

Abstract: Laser shock peening (LSP) was used to strengthen the surface properties of friction stir welding (FSW) joint for 7050-T7451 aluminium alloys. The microstructure, precipitates, dislocations and electrochemical corrosion properties in the surface of weld nugget zone (WNZ) and heat-affected zone (HAZ) of FSW joints were analyzed. The microstructure experienced an obvious change in the cross-section region close to the upper surface of WNZ and HAZ after LSP. The number of precipitates near the grain boundary increased obviously after the LSP. The dislocation in the shock region mainly shows the dislocation line, dislocation tangle, dislocation walls and sub-grain structure (Grain size 2–3 μm). The surface of as-received shows the highest corrosion potential (−0.835 V) in a 3.5% NaCl solution, and the corrosion potential in the surface of WNZ (−0.898 V) and HAZ (−0.932 V) after LSP is higher than the one before LSP. Grain refinement, precipitates and high density dislocation could play an important role to improve the corrosion resistance in the surface of WNZ and HAZ after LSP.

Residual stress, phase, microstructure and mechanical property studies of ultrafine bainitic steel through laser shock peening

Abstract: The aimed study proposes laser shock peening without a coating of high strength ultrafine bainitic steel to mitigating the fatigue failures for automotive and structural engineering applications. Laser pulse density of 2500 pulses/cm2 (75% overlapping) was optimised based on the induced residual stresses for employing the wide range of characterisations. The roughness and topographic results showed that surface roughening was controlled by tuning the laser pulse density. The High-Resolution X-ray Diffraction analysis confirmed the lattice misorientation resulting peak shift and the trend towards martensite phase transformations. The electron microscopic micro/nanostructure analyses revealed the grain refinement features such as nano-twins, micro shear bands and shear cells. The work hardening depth analysis indicates the significant enhancement in the mechanical properties. Completely reversed (R = −1) high-cycle fatigue tests extended the lifespan by an average of five times than the untreated. Also, it has potential to repair the structural components effectively.