Peening Treatment Research Articles

Use of Power Series Expansion for Residual Stress Determination by the Incremental Hole-Drilling Technique

The integral method of incremental hole-drilling is used extensively to determine the residual stress distribution in isotropic materials. When used with Tikhonov regularization, the method is robust and produces accurate results with minimal uncertainty. Alternatively, an optimal hole depth distribution can be found using the method of Zuccarello to improve the conditioning of the calibration matrices. If substantial measurement noise or a steep variation in stress exists, however, considerable uncertainty in, or distortion of, the calculated residual stress distribution can occur. Series expansion offers an alternative solution, but it has been reported to become unstable before meaningful accuracy can be achieved. Investigate the use of series expansion to determine a rapidly changing throughthickness residual stress distribution in an aluminium alloy 7075 plate subjected to laser shock peening treatment. Power series expansion of eigenstrains is used in finite element modelling to calculate the calibration coefficients. Monte Carlo simulation is used to determine robust uncertainties in the residual stress distributions. This allows the series order with the lowest RMS uncertainty in stress to be selected from those series orders that have converged. The best estimate of the residual stress distribution is thereby obtained. Series expansion is shown to be stable up to 8th order and convergence to a stress solution can be found before instability dominates. The method is insensitive to measurement errors due to the least-squares approach employed by the inverse solution. The use of series expansion reduces the RMS uncertainty in stress when compared to the regularized integral and Zuccarello methods.

Effect of warm shot peening treatments on surface properties and corrosion behavior of AZ31 magnesium alloy

Magnesium alloys are considered as a suitable choice for temporary biodegradable implants due to their biocompatible and biodegradable properties, able to avoid a second surgery when implant removal is needed. Nevertheless, nowadays one of the shortcomings of magnesium-based materials is their poor corrosion resistance and the associated high corrosion rate. This fact considerably hinders their application in biomedical field. The aim of this work is to induce a severe plastic deformation on the upper layer of the AZ31 Mg alloy in order to modulate its surface properties to slow down the kinetics of the corrosion damage. Specimens were submitted to conventional and severe shot peening treatments at room temperature, 240 °C (near recrystallization temperature) and 360 °C (above recrystallization temperature); the specimens were then analyzed in terms of grain refinement, surface roughness, work hardening, and residual stresses. Potentiodynamic polarization tests were also performed to evaluate the influence of the shot peening treatments on the specimens' corrosion resistance. The results evidenced surface roughness as the most influential factor in corrosion behavior, although for the specimens with similar roughness, also the effect of grain size is notable.

Comparison Between Confined and Unconfined Laser Peening Effect on the Fatigue Life of Composite Materials

Mechanical Engineering Department/ University of Technology- Baghdad.
 Confinement layer is considered as the most important parameter during the laser shock peening (LSP) treatment. In this paper, its effect on the surface treatment effectivity of composite materials was investigated. The composite used in this research was fabricated using hand lay-up as a manufacturing process. The matrix material was built from unsaturated polyester resin and reinforced with 2.5% volume fraction of micro particles of aluminum powder. Fatigue test was conducted at room temperature with constant amplitude stress and a stress ratio of R =-1, before and after LSP treatment. LSP was applied with and without confinement layer at the same level of energy after the specimens were coated with a black paint. The results manifested that the laser peening without confinement layer increased the endurance limit by about 13.296% compared with the untreated state. Whereas using water as a confinement layer during treatment reduced the endurance strength by about 18.133% compared to the untreated state. Also, it was observed that the difference between confined and unconfined LSP effects on the endurance limit was about 31.429%.

The Effects of Shot Peening on the Surface Characteristics of 35NCD16 Alloy Steel

Shot-peening is a surface mechanical treatment, widely used to treat metallic parts in the aerospace and automotive industries. This mechanical surface treatment should not be confused with other common applications of other peening treatments, oriented towards cleaning, preparation or surface finishing. Shot peening is a mechanical treatment used to improve the service life of metallic components, especially when they are submitted to cyclic loads. The effect of shot peening on the surface work hardening and residual stress profile of a 35NCD16 steel was studied in this work.

Influence of high-energy shot peening on the microstructure and mechanical properties of Ti–6Al–4V welded joints

In this study, Ti–6Al–4V welded joints were subjected to a high-energy shot peening (HESP) treatment. The structural characteristics of the Ti–6Al–4V welded joints were investigated by optical microscopy (OM) and x-ray diffraction (XRD). The Rockwell hardness and residual stress in different regions of the Ti–6Al–4V welded joints were assessed before and after treatment. Tension tests were then performed to investigate the effect of HESP on the welded samples. Experimental results showed that an Surface nanocrystallization (SNC) layer can be prepared on a Ti–6Al–4V welded joint via HESP. The average grain size of the SNC layer was approximately 30 nm after HESP. HESP also resulted in a higher surface hardness compared with that of the original sample. After treatment, surface compressive residual stresses formed in welded joints, and the residual peak stress of the weld zone was decreased from 650 MPa to −638 MPa. The surface hardness and surface residual stress were distributed more uniformly on the surface of the welded joint. After treatment, the tensile properties were improved.

Improvement the Mechanical Characteristics of Alloy Steel DIN 41Cr4 by Shot Peening

The effects of shot peening treatment (SPT) were studied at (10,20, and 30) minutes on the rotating bending fatigue behavior and the behavior of the alloy steel DIN 41Cr4 vibrations. The hardness test, tensile test, constant amplitude fatigue tests, and the vibration measurements were performed on samples with and without cracks at room temperature (RT), also, the fracture surface was examined and analyzed by a Scanning Electron Microscope (SEM). The results of the investigations, for example, Stress to Number of cycles to failure (S-N) curves, fatigue strength improvement factor of 5% to 10%, the decreasing percentage of maximum Fast Fourier Transform (FFT) acceleration of the shot-peened condition were compared to untreated conditions ranging between 25% and 40%. All these improvements occurred for up to 20 minutes of shot peening time (20 SPT), exceeding that time the fatigue behavior tended to decrease due to high roughness and the generation of tensile residual stress.

Fatigue life enhancement in alpha/beta Ti–6Al–4V after shot peening: An EBSD and TEM crystallographic orientation mapping study of surface layer

Shot peening is a well-established surface treatment technique to improve metallic components’ fatigue lives by introducing compressive residual stress at their surface layers. Using α/β Ti–6Al–4V alloy as an example, the fatigue life of Ti64 was significantly enhanced after a compressive residual stress was introduced to a depth of 208 µm via shot peening treatment. The top ~24 µm layer from surface was found interestingly unable to be indexed under electron backscatter diffraction (EBSD), a depth coinciding with the presence of maximum compressive residual stress as revealed by center hole drilling method. Transmission electron microscope (TEM) with crystallographic orientation mapping was therefore employed to probe the top surface layer in order to unveil the origin of such thick non-indexed region observed in EBSD after shot peening and its effect on enhancement of component's fatigue life.

Experimental investigation on ultrasonic shot peening of WC-Co alloy

ABSTRACT Ultrasonic surface shot peening (USSP) treatment was conducted on the WC-8Co composite. The effects of different USSP-treated time on surface roughness, microstructure, mechanical and corrosion resistance were investigated. The results show that continuous bombardment on the surface of WC-8Co cemented carbide induced by high kinetic energy particles during USSP makes the WC particles and Co phase broken and refined. A nanostructured layer is generated on the top-surface of WC-Co cemented carbide and the thickness is about 3.14 µm. Due to the polishing and washing of all samples, the results of surface roughness don’t change much. Microhardness of nanostructured surface layer increases by 15.8% compared with the untreated sample. Electrochemical experiment results indicated that the refinement of grain are the main reasons for the enhanced corrosion behavior of the samples. At the same time, the most suitable shot peening time of USSP for WC-8Co cemented carbide is 30 min.

Experimental Analysis of Residual Stress and Bending Strength of Gear Tooth Surface after Shot Peening Treatment

The fatigue strength of a gear tooth surface is affected by various factors, which subsequently impacts the transmission performance of gears. Usually, shot peening treatment is carried out during processing to improve the performance of gears. Most current studies focus on theoretical descriptions and simulation analyses of shot peening treatment. However, in this paper, the relationships among shot peening treatment, residual stress, and bending fatigue strength of a gear tooth surface are discussed, through experimental methods. Based on X-ray stress analysis, at select locations on the test samples, the residual stresses on gear tooth surfaces with and without shot peening treatment are determined and contrasted. The results show that shot peening treatment can effectively increase the residual stress on gear tooth surfaces. In addition, an electromagnetic resonance fatigue tester is used to analyze the bending fatigue strength of gear tooth surfaces. The test results indicate that the bending fatigue strength of the gear teeth with shot peening is higher than that of the gear teeth without shot peening. The obtained conclusions lay the foundation for further practical engineering applications of gears.

Optimization of Shot Peening Effective Parameters on Surface Hardness Improvement

Shot peening is well-known process for mechanical properties integrity in metallic materials. In present study influences of different shot peening treatments on the surface hardness of different carbon steels were investigated experimentally and then alternative approach by using artificial neural network is presented for hardness prediction of the shot peened surface. After modeling a comprehensive parametric investigations and sensitivity analysis were applied according to the influence of the related effective parameters on surface hardness improvements.

Microstructural evolution and mechanical properties of selective laser melted a nickel-based superalloy after post treatment

Although additive manufacturing (AM) has developed significantly due to its numerous process advantages, some adverse effects include large columnar grains and detrimental tensile residual stress, which can weaken the performance of the final part. In this study, a new post-treatment method combining heat treatment and laser shock peening was employed to alter the microstructure and mechanical properties of AM-processed Inconel 625 alloy (IN625). The microstructural evolution of IN625 after different treatments was studied. Results showed that many γ′' precipitates were formed after heat treatment. After heat treatment followed by laser shock peening treatment, gradient microstructure along depth direction was generated. High-density dislocation structures and refined grains were produced in the subsurface layer after heat treatment followed by laser shock peening treatment. Moreover, the precipitates interacted with dislocations. High levels of compressive residual stress could be generated after heat treatment followed by laser shock peening treatment, resulting in high ultimate tensile strength and large elongation. This combined heat treatment and laser shock peening method is helpful in enhancing the mechanical performance of AM parts through changing their microstructure and residual stress distribution.

Laser processing of Mg-10Li-3Al-3Zn alloy：Part II- Improving corrosion resistance of multi-phase Mg alloys by laser surface processing

In Part Ⅰ of this series, it can be found that the corrosion resistance of metals in the welded seam zone (WSZ) was far higher than that of the base metal (BM) of MBLS10A-200 Mg-Li alloy. Therefore, the feasibility of improving the corrosion resistance of MBLS10A-200 Mg-Li alloy through laser surface melting (LSM) was further explored. Meanwhile, laser shock peening (LSP) treatment was also used for contrast. The results showed that the surface melted zone with the corrosion resistance through LSM superior to that of metals in WSZ of MBLS10A-200 alloy through laser welding can be prepared by controlling heat input through increasing the scanning speed of laser beam, while LSP has limited impact on the electrochemical corrosion resistance of MBLS10A-200 alloy. The corrosion current density (Jcorr) of the samples subjected LSM declined by two orders of magnitude compared with the base metal (BM) while the charge transfer resistance increased by 17 times compared with BM. An analysis indicated that owing to the fast cooling rate during laser processing, the multi-phase microstructures (i.e. α phase, β phase and Li2MgAl) of BM were transformed into β single-phase microstructure in WSZ and surface melted zone. In this way, not only solid solution strengthening of the metals in WSZ was realized but also the micro-galvanic coupling generated due to the difference of electric potentials of multi-phase microstructures were reduced, thus improving the corrosion resistance of surface melted zone.

A study of the corrosion behavior of AZ31 Mg alloy in depth direction after surface nanocrystallization

The ultrasonic shot peening (USSP) treatment formed a nanocrystalline surface layer and a gradient microstructure of 200 μm depth. Corrosion test of the USSP treated and certain layers of surface materials being removed by polishing was performed. It was found exfoliated Fe particles during USSP increased the corrosion rate. The Fe particles provided more cathodic reaction sites during the corrosion process, leading to an obviously increased current density of the cathodic reaction. The nanocrystalline resulted in a fast formation of protective film and the high density of grain boundary acted as an effective corrosion barrier, which reduced the current density of the anodic reaction. The work provides an efficient way to investigate the effect of grain size and other factors on the corrosion resistance by measuring the corrosion rate of the gradient nanostructure along the depth.

Effect of shot peening coverage on residual stress and surface roughness of 18CrNiMo7-6 steel

Shot peening is becoming a widely used surface strengthening technique for various key mechanical components for its enhanced influence on the fatigue performance. This technique allows to strengthen the mechanical properties of material via introduce a certain depth of compressive stress layer and change the surface topography. The relation of the shot peening processing parameters, the surface integrity including residual stress and the surface roughness remains a large unmet practical need. In this paper, the residual stress and surface topography obtained by various shot peening treatments were experimentally and theoretically examined. A random multi-shots peening model of a carburized roller, accounting for the initial hardness gradient and residual stress was developed. The measured residual stress and surface roughness present good agreements with the predicted results. Both the experimental and simulated results reveal that the axial and tangential residual stress components tend to be consistent after shot peening. In addition, the influence of peening coverage on detailed evolution of surface topography and residual stress is investigated. It is found that the ratio between the layer thickness of compressive stress and the critical depth of maximum stress generally lies in the regime of 3.6–4.3 after shot peening. As the coverage increases from 100% to 400%, surface roughness parameters Sa, Sq, S5z, Sku decrease, while the maximum magnitude of compressive stress fluctuates in the range of 1105∼1230 MPa. This work could act as an advisory reference for shot peening engineering practices.

Strengthening the FeCoCrNiMo0.15 high entropy alloy by a gradient structure

In present work, a gradient structured FeCoCrNiMo0.15 high entropy alloy (HEA) is processed by shot peening treatment. Microstructures of the gradient structured HEA are characterized by electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI) and transmission electron microscopy (TEM). Complex microstructures consisting of nanograins, nanotwins, with high densities of dislocations are formed on the surface of the shot peening treated HEA. With the increase of depth from surface to center, a planar dislocation slip occurs while no deformation twin is observed. Un-deformed grains were observed in the regions of ∼100 μm–150 μm depth from the surface. Such gradient structured HEA shows an increase of yield strength from 418 MPa to 486 MPa when compared to the one with homogeneous structure, with a slight decrease in tensile elongation from 50.9% to 46.8%. During tensile deformation, strong deformation twinning including the formation of hierarchical nanotwins occurs in the gradient structured HEA. These unique deformation microstructures are associated with high strain hardening and show increased ductility, which creates excellent combination of strength and tensile elongation. Our work offers valuable insight into achieving high-performance HEAs.

Surface Grain Refinement of 304L Stainless Steel by Combined Severe Shot Peening and Reversion Annealing Treatment

The present study proposes a novel method, i.e., combined severe shot peening (SP) and reversion annealing treatment, to grain-refine the surface layers of 304L austenitic stainless steel. Steel specimens were shot-peened at 0.7 MPa for 30 min, introducing 40% vol. α′ martensite, and then were annealed at 700 or 800 °C for different durations (30 s). As annealing reversed α′ martensite to austenite, the obtained surface layers consist of fully austenitic ultrafine grains. The smallest grain size obtained is about 500 nm at the top surface. SP elevates the microhardness to more than 500 HV. Although the grain-refined surface layers produced by the combined method are not as hard as that treated by only SP, they are harder (e.g., the specimen annealed at 700 °C for 30 s using a heating rate of 50 °C/s exhibited a peak microhardness of 400 HV) than the untreated surface layer (225 HV) due to grain refinement. Moreover, due to the absence of α′ martensite, they have higher corrosion resistance in H2SO4 solution than that treated by only SP.

Surface modification of NiTi alloy by ultrashort pulsed laser shock peening

This research paper presents the attempt at ultrashort pulsed laser shock peening with absence of absorptive layer and confining medium which could enhance surface microhardness and the abrasion property of NiTi shape memory alloy. The average roughness values of NiTi specimen were measured on the surface, because the roughness would affect the friction resistance. The microhardness and Young's modulus were investigated at different position of single laser spot by nanoindentation technique. The pin-on-plate sliding abrasion testing were performed with different load-force (0.5 N and 2 N) for different testing time. Results showed that ultrashort pulsed laser shock peening treatment would cause a significant improvement on friction coefficient and abrasion property, which was attributed to the change of surface modification, such as roughness, microhardness, microstructure and titanium oxide layer, but the ultrashort pulsed laser shock peening treatment did not enhance its tensile strength during present research.

A dislocation density–based comparative study of grain refinement, residual stresses, and surface roughness induced by shot peening and surface mechanical attrition treatment

A dislocation density–based comparative study of grain refinement, residual stresses, and surface roughness induced by shot peening and surface mechanical attrition treatment

Electrochemical corrosion behavior of a magnesium calcium alloy in simulated body fluids with different glucose concentrations

This paper investigates the effect of glucose concentration on the electrochemical corrosion behavior of a magnesium calcium alloy in Hanks’ simulated body fluid (SBF) using potentiodynamic polarization and electrochemical impedance spectrum (EIS) methods. The results indicate that the corrosion potential of magnesium calcium alloy decreased slightly from −1.34V to −1.49V with increasing the glucose concentration from 0.7g/L to 1.6g/L. Comparatively, the corrosion current density decreased from 2.038mA/cm2 to 0.031mA/cm2, indicating that the corrosion rate was inhibited effectively by a high glucose concentration. Crevice corrosion was found to be a dominant corrosion mode under all investigated glucose concentrations. In addition, wet peening treatment was proved to be a promising method to improve the corrosion resistance of magnesium calcium alloy. The corrosion rates were decreased by over 60% using wet peening treatment. The research provides a fundamental understanding of the corrosion behavior and associated corrosion mechanism of magnesium calcium alloy within different body fluid environments.

Improvement of high temperature oxidation resistance of additively manufactured TiC/Inconel 625 nanocomposites by laser shock peening treatment

Additive manufacturing has seen large growth due to its numerous process advantages, yet some undesirable defects in additive manufactured (AM) products include pores and micro-cracks. These defects weaken the high temperature oxidation resistance of the final parts. In this work, laser shock peening (LSP) is used as a post-treatment method to change the surface characteristics of selective laser melted (SLM) nano-TiC particle-reinforced Inconel 625 nanocomposites (TiC/IN625). The effects of LSP on surface morphology, residual stress, microhardness, microstructure, and high temperature oxidation behavior of fabricated parts are studied. The results indicate pores in the as-built sample can be closed by the severe plastic deformation, which is induced by LSP. The maximum hardness is found to reach 462 ± 7 HV with a ∼ 460 μm hardened layer, and the surface stress state transforms from tensile to compressive after LSP. The full width at half maximum (FWHM) values of the (111) and (200) diffraction broaden, which can be attributed to grain refinement and an increase in lattice strain in the LSP samples. It is found that LSP causes a large number of columnar dendritic structures in the as-built sample to transform into cellular dendritic structures. Dislocation walls and dislocation tangles with high dislocation density form in the LSP sample. Compared with as-built sample, the LSP samples exhibit lower mass gain after oxidation at 900 °C for 100 h, indicating that LSP samples have greater oxidation resistance at high temperature. The underlying mechanism governing the high temperature oxidation resistance is proposed based on the experimental results. This study shows that LSP can be used as an effective method to modify the surface characteristics of SLM TiC/IN625.