Effect Of Shot Peening Research Articles

The effect of shot peening on the corrosion behaviour of Ti-6Al-4V alloy made by DMLS

Abstract Additive Manufacturing processes are being used increasingly in the scope of medicine and dentistry. As indicated by literature data, the durability and quality of medical implants is decisively influenced by surface modification. Insufficient quality of surface finishing leads, among others, to reduced service life of applied implants and to increased number of necessary revision surgeries. Furthermore, various types of finishing processes e.g. cleaning, shot peening or abrasive techniques are suggested by the manufacturers of products made by means of DMLS processes. Due to this fact, the analysis of proper formation of the surface layer of titanium products made by means of the method consisting in the direct laser sintering of metal powders (DMLS) was the subject matter of our research. Therefore, Ti-6Al-4V titanium alloy has been used for tests. The samples have been produced by means of EOSINT M280 system dedicated for laser sintering of metal powders. The surfaces of prepared samples have been subjected to shot peening process at three different values of working pressure (0.2, 0.3 and 0.4 MPa) by means of three different working media i.e. CrNi steel shot, crushed nut shells and ceramic balls. The characteristics of the materials used for shot peening process have been determined by means of Zeiss Ultra Plus scanning electron microscope. The samples have been subjected to profilometric measurements on Bruker Contour GT optical profilometer and the corrosion behaviour of Ti-6Al-4V titanium alloy in Ringer solution has been determined in electrode impedance spectroscopy (EIS) measurements by means of Atlas 0531 set dedicated for corrosion testing. The overall results of all tests indicate to favourable influence of the shot peening process on the corrosion behaviour of titanium alloy.

Effect of Shot Peening on Oxidation Behavior of SS304H Upon Long Term Steam Exposure.

Specimens of austenitic stainless steel 304H (SS304H) were shot peened and exposed to steam at 600, 650, and 700 °C for 10,000 h, 15,000, and 20,000 h. After steam exposure, un-peened SS304H has three oxide layers, Fe-O, Fe-Cr-O and Cr2O3, while shot peened specimens have an Fe-Cr-O layer, a Cr2O3 and an amorphous Fe-Si-O layer. The evolution of the oxide layers as a function of duration of steam exposure and temperature reveals that the growth of the Fe-O and the Fe-Cr-O layers is inhibited by shot peening. The oxide layers in shot peened specimens are much thinner, indicating that shot peening enhances the oxidation resistance of SS304H. Grain refinement during shot peening enhances the diffusion of Cr and Si to help form a protective, oxidation resistant surface.

Microstructural Evolution of Super304H Upon Ultrasonic Shot Peening and Subsequent Annealing.

In this study we analyze the effect of shot peening on the microstructure and mechanical properties of Super304H, which is widely used for boiler tubes. Specimens were shot peened for 5, 10, and 15 minutes, and then heat treated at 600, 700, and 800 °C for 15 minutes. Vickers hardness was measured and the microstructure of cross sectional specimens was analyzed by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). Heat treatment led to particle refinement on the upper layer of Super304H. In this region, nanograins, twins, and dislocations were generated to a depth of ~400 μm. The microstructure of the shot peened specimen did not change even after a heat treatment at 700 °C. However, rapid grain growth was observed after rapid annealing at 800 °C. Precipitation hardening occurred after heat treatment at 800 °C.

Effect of severe shot peening on corrosion behavior of AZ31 and AZ91 magnesium alloys

Severe shot peening (SP) was performed on the AZ31 and AZ91 Mg alloys to obtain a nanostructured surface layer. The microstructure, micro-hardness and corrosion behavior of AZ31 and AZ91 Mg alloys after SP treatment were studied using transmission electron microscopy, micro-hardness tester and corrosion tests, respectively. Results showed that SP treatment produced a plastic deformation layer with α-Mg grains at the nanometer scale in the surface of AZ31 and AZ91 Mg alloys. After SP treatment, the micro-hardness in the near surface region displayed an obvious increase for two alloys, owing to the combination of the grain refinement and the work-hardening. The corrosion resistance of AZ31 alloy was improved by SP treatment, because a relatively compact passive film formed rapidly on the nanostructured surface. Unfortunately, SP treatment played a minor role in enhancing the corrosion resistance of AZ91 alloy, because it had little effect on size and distribution of β-phases.

Optimization of USSP duration for enhanced corrosion resistance of AA7075

This investigation was carried out following our earlier work on the effect of ultrasonic shot peening (USSP) on corrosion resistance of the 7075 aluminium alloy in 3.5 wt% NaCl solution to optimize the duration of USSP. The samples not treated with USSP and different samples treated with USSP were subjected to potentiodynamic polarization and electrochemical impedance spectroscopy. Among the specimens USSP treated from 5 to 30 s, the one USSP treated for 15 s (USSP 15) was found to exhibit highest corrosion potential (Ecorr) and lowest corrosion current density (icorr). Corrosion products were characterized by Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). Scanning Kelvin Probe Force Microscopy (SKPFM) was used to measure the surface free potential. The enhanced corrosion resistance of the USSP 15 sample was found to be due to combined effect of surface nanostructure of the matrix, homogeneity and refinement of second phase precipitates. There was enhancement in formation of adherent passive layer in the USSP15 specimen.

Thermal growth of exclusive alumina scale on a TiAl based alloy: Shot peening effect

Shot peening, although generally accepted as a useful surface treatment method to improve oxidation resistance of Ni-, Co- and Fe-based alloys, has been less applied to TiAl based alloys. This work shows that a shot peening treatment converts the Ti-45Al-2Nb-2Mn-1B alloy from thermally growing TiO2-Al2O3 mixed oxides to an exclusive Al2O3 in air at 900 °C. The basic reason for this is that the shot peening catalyzes formation of an α-Al2O3 thin film, which prevents Ti of the alloy from oxidation at the high temperature. The slow oxidation of the shot-peened alloy mitigates the degradation of typical γ/α2 lamellar microstructure.

The negative effect of high-intensity shot-peening on the intergranular corrosion behavior of the Super304H austenitic stainless steel

The influences of high-intensity shot-peening (SP) on the microstructure and intergranular corrosion susceptibility (IGCS) of the Super304H stainless steel during aging were investigated. The high-intensity SPed samples exhibited a quicker sensitization and desensitization process when aging at 650 °C, in comparison with the low-intensity SPed and coarse grained counterparts. With aging time increase from 24 h to 168 h, however, their IGCS increased again because the high energy stored inside the highly deformed surface promoted the recrystallization process and the formation of σ-phase was accelerated at the recrystallizing interfaces with low nucleation energy barrier and induced additional Cr-depleted zones.

Effect of Ultrasonic Shot Peening on Microstructural Evolution of Duplex Stainless Steel S32750

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The effect of high energy shot peening on microstructure and joining strength of TIG welded AZ31B weldment

The effects of high energy shot peening on the microstructure and mechanical properties of TIG welded AZ31B magnesium (Mg) alloy joints were investigated. The surface characteristics, surface residual stress, tensile strength, grain size and dislocation density were characterized by the experimental observations. Results show that the surface defects were eliminated, tensile residual stress was turned into compressive residual stress and superior joining strength were obtained after HESP treatment under the pressure of 0.15 MPa. A nanoscale layer was obtained in the surface layer and the hardness was significantly increased in the surface layer. Large amounts of dislocations also generated with the aid of HESP treatment. All these factors contributed to the significant improvement in mechanical performance of the Mg alloy joints, leading to a notable enhancement (14.0%) in tensile strength of treated joints to 262.3 MPa over the joints without HESP treatment (230.08 MPa).

Do corrosion pits eliminate the benefit of shot-peening?

The impact of corrosion pits on the beneficial effect of shot-peening of 12Cr steam turbine blade steel has been evaluated under fatigue loading conditions in air. The fatigue limit was measured for pits of depth in the range 50 μm–300 μm, typical of depths to be expected in a reasonably well-managed operating plant but with occasional transient excursions in water chemistry. X-ray diffraction (XRD) measurements indicated that the compressive residual stress approached zero at a depth of about 250 μm, yet a significant benefit of this residual stress on the fatigue limit was still retained with the pit of depth 300 μm. An explanation could be found in finite element analysis, which predicted a reduced net tensile stress range and mean stress at the base of the pit in the shot-peened specimen. The fatigue crack growth rate from a corrosion pit was also reduced by the residual stress, until the crack attained a depth of 0.9 mm. well beyond the depth of compressive residual stress. An explanation based on constraint to lateral crack propagation near the surface and its impact on stress intensity factor at the crack base is proposed.

Local microstructure inhomogeneity and gas temperature effect in in-situ shot-peening assisted cold-sprayed Ti-6Al-4V coating

In the cold spraying process, previously deposited particles are hammered by the following particles, and gas temperature plays an important role in coating properties. In this study, By adding large shot peening particles to original Ti-6Al-4V (TC4) powder, five in-situ shot peening assisted cold sprayed coatings were obtained using nitrogen accelerating gas at different temperatures, and microstructure and the mechanical properties of coatings were evaluated. No phase transformation occurred during the spraying process, and the deposition efficiency was generally more than 60%. The cross-section morphology showed that the coating became denser with the increase in temperature, and the coating showed a structure of alternating dense and porous regions. Local regions struck by large shot-peening particles were denser than other regions. Therefore, the porosity, microhardness, and elastic modulus were divided into two categories. These two categories showed the same trend with temperature: The porosity decreased, whereas the microhardness and elastic modulus gradually increased. The highest values of the latter two properties were 443.4 HV0.3 (tamped region)/390 HV0.3 (nontamped region) and 124.8 GPa (tamped region)/110.2 GPa (nontamped region), respectively. Moreover, the bonding and shear strengths increased as the temperature increased, and the fracture morphology showed that brittle fracture was the main type of failure. In addition, by analyzing the microstructure and action depth of shot at different temperatures, it was found that the auxiliary effect of shot peening on the deformation of particles was limited at high gas temperature.

Effect of shot peening on microstructure, hardness, and corrosion resistance of AISI 316L

Purpose: This research conducted to analyse the effect of shot peening on surface structure, hardness, and resistance to corrosion of AISI 316L. Design/methodology/approach: The shot peening process is carried out on the surface of 316L stainless steel samples with four peening durations, and they are 2, 4, 15, and 30 minutes. Shot ball steel with diameter 0.4 mm for metal shot blasting and model S110 of ISO 11124/3 and SAEJ827, with the chemical composition, are C (0.8-1.2 wt.%), Mn (0.6-1.2 wt.%), Si (min. 0.4 wt.%), S (max. 0.05 wt.%), P (max. 0.05 wt.%), with a hardness of steelball, about 40-50 HRC. The pressure of compressor kept constant at 8 bar with a diameter of the nozzle is 5 mm, and the distance between the nozzle and the sample surface variated by 6 cm and 12 cm for each shooting duration. Findings: The result shows that the shot peening increases the surface hardness of the material, changes the microstructure on the surface layer and increases the resistance to corrosion. Shot peening with 30 minutes of shooting duration and 6 cm of shooting distance can improve the metal surface properties, which has a surface hardness of 772.23 HV and good on corrosion resistance. Research limitations/implications: The results of this experiment show that shot peening distance of 6 cm for 30 minutes achieved the highest surface hardness of AISI 316L. The corrosion rate decline with increasing duration and nearer distance of shooting balls. Practical implications: In the development of the implant material, AISI 316L need to be improved, its material properties, so it can be used safely and compatibly. Shot peening is a cold working process of metal to increase the material properties by shooting the steel ball into the surface of a material. Originality/value: Based on the experimental results it was obtained that variations shot peening distance and shot peening duration can change grain morphologies, subsequently affect hardness and corrosion resistance on AISI 316L.

Discrete element-periodic cell coupling model and investigations on shot stream expansion, Almen intensities and target materials

Shot peening is a cold-working process widely used to enhance the fatigue life of metallic components. This process consists of propelling thousands of spherical particles onto a ductile metallic surface. This paper presents a sequential coupled discrete element (DE)-periodic cell based finite element (FE) model to predict the shot peening effects, in terms of residual stresses and surface roughness. Shot stream expansion was accounted for and distribution of shots impacting velocities was extracted in discrete element model (DEM). Shot peening effects were computed on an impacting zone represented by a periodic cell. A cyclic material model was used to describe the plastic properties of the targets. Shot peening on IN718, 300M and AA7050 with CW14, S230 and Z425 shots at 4A and 8A Almen intensities were simulated to investigate their influences on the distribution of shot impacting velocities, residual stress profiles and surface roughness at full coverage. Numerical results show that accounting for shot stream expansion leads to residual stress profiles that are closer to those experimentally measured than assuming a cylindrical shot stream. The predicted residual stress profiles and surface roughness are comparable to the experimentally measured values, for the three materials studied.

Comparative study of the effects of surface mechanical attrition treatment and conventional shot peening on low cycle fatigue of a 316L stainless steel

In this work, the effects of surface mechanical attrition treatment (SMAT) and conventional shot peening (CSP) are comparatively studied on the surface characteristics and low cycle fatigue (LCF) properties of a 316L stainless steel. For this purpose, surface topography, residual stress and work hardening are evaluated on the treated samples. Both CSP and SMAT are performed with the same Almen intensity and the same coverage. Total strain controlled LCF tests are carried out in order to compare the effects of these two techniques on the fatigue properties of the studied steel. The results show that the samples treated by SMAT and CSP exhibit similar trends of cyclic stress amplitude evolution, and higher mechanical strength than the untreated samples. However, the samples treated by CSP manifest higher fatigue life under low strain amplitude (±0.5%), but lower fatigue life under high strain amplitude (±1.25%), compared to the SMATed samples. The fatigue life results are discussed based on the analysis of different characteristics including surface topography, microstructure, residual stress and its relaxation, as well as fracture surfaces.

Effect of Shot Peening on the Surface Integrity and Notched Fatigue Properties of a Single-crystal Superalloy at Elevated Temperature

The surface integrity and notched fatigue property of a shot-peened single crystal superalloy were investigated. The surface texture of the peened material was determined using a white light interferometer, while the microstructural characterization was performed using a scanning electron microscopy, high resolution transmission electron microscopy from the plane and cross-section view directions and electron backscatter diffraction. The gains, expressed in term of high temperature fatigue limit, were established by rotating-bending fatigue tests and discussed in relation to the microstructure evolution in the shot peening states. Results show that the beneficial effect provided by shot peening is more than 14.8% against the as-machined in a temperature range from 760 °C to 850 °C because of the high-density tangled dislocation, cold work and disorientation. Furthermore, the stress concentration coefficient is reduced by the shot peening procedure while the average profile height Ra increases according to the calculation of the surface stress concentration.

Microstructure and nanoindentation hardness of shot-peened ultrafine-grained low-alloy steel

The effect of shot peening (SP) on microstructure and hardness of ultrafine-grained (UFG) low-alloy steel was investigated. With increasing shot-peening time from 0.5 to 1.5 h, grain size of UFG low-alloy steel decreases from 400 to 280 nm at surface whilst that of the layer with a depth of 160 μm decreases from (230 ± 15) to (75 ± 5) nm. Interestingly, nanoindentation shows that hardness increases linearly with increasing the SP duration, reaching a value as high as (7.10 ± 0.1) GPa at the depth of 160 µm after the SP duration of 1.5 h. The thickness of the SP treated layer is measured as ~ 300 μm. The Hall–Petch (H–P) relationship was established for the hardening layer. Correspondingly, abrasion resistance should be ~ 51% higher than that of as-prepared UFG low-alloy steel. As shown in SP processing, grain refinement is the key factor responsible for the strengthening of the studied steel.

FE analysis of shot-peening-induced residual stresses of AISI 304 stainless steel by considering mesh density and friction coefficient

ABSTRACT In order to investigate the effect of shot peening (SP) on residual stress distribution of AISI 304 stainless steel, a 3D dynamic model for describing single and multiple shot impact phenomenon was built via ABAQUS/Explicit 6.10 by considering the mesh density of treated component as well as the friction coefficient between shot and treated component and validated via X-ray residual stress measurement. The results show that an optimal surface element size about 1/18th of the dimple diameter and reasonable friction coefficient of μ > 0.2 are the key factors for the accuracy of residual stress estimation and the computational efficiency. The error of simulated residual stresses indicates the effect of the deformation-induced martensitic transformation phenomenon should be considered in AISI 304 stainless steel SP model. The effects of shot hardness, impact angle, velocity, diameter and coverage ratio on residual stress distribution were examined and discussed via the optimised SP model.

Enhancement of surface characteristics of direct metal laser sintered stainless steel 316L by shot peening

The present work deals with the enhancement of the surface characteristics of stainless steel (SS) 316L fabricated through use of direct metal laser sintering (DMLS) process. Centrifugal type shot peening was performed using cast steel shots for improvement to the as-built surface quality. Shot peening leads to significant enhancement on the surface topography, which provided a trough profile with roughly spherical dents. The needle-like surface peaks which are generally observed on the as-built DMLS surface was also eliminated. In addition, the effect of shot peening was found to be more significant on the roughness parameters leading to 50% of reduction in the average surface roughness. The micro Vicker's hardness test led to the observation of an increase in the average surface hardness of the shot peened layer from VHN 230 to VHN 324. Microstructural examination after peening showed severe plastic deformation with laterally stretched grains on the surface. Further, X-ray diffraction analysis confirmed the presence of surface grains with high dislocation density. There was no phase transformation following shot peening i.e. conversion of austenite into strain induced martensite. The observations made from the current investigation would find new applications for SS 316L fabricated through use of DMLS process.

Influence of Microstructure on Shot Peening Effects of Ti-6Al-4V Alloy

Ti-6Al-4V alloys with equiaxed, martensitic and lamellar microstructures, respectively, were shot peened. Microstructure observation, phase analysis and surface residual stress measurement were conducted to investigate the microstructure influence on shot peening effects. The experimental results indicate that after shot peening microstructure of surface layer became fine and homogeneous for the as-received alloy which showed equiaxial microstructure. Cracks were found in the surface layer for the sample with acicular martensitic microstructure. And the sample with coarse lamellar structure transformed to equiaxed microstructure in the surface layer. Surface residual stress showed obvious difference. The samples with equiaxed microstructure achieved a compressive residual stress of 660 MPa, the ones with acicular martensitic microstructure achieved 366 MPa, and the ones with coarse lamellar microstructure showed a residual stress only 125 MPa.

An Energetic Approach to Predict the Effect of Shot Peening-Based Surface Treatments

Almen intensity and surface coverage are well-known to be the defining parameters of shot peening-based surface treatments. These parameters are directly affected by material properties, the extension of the contact zone, the geometry of the impact pair, as well as the impact rate and velocity. Such intricate relationships have resulted in often dissimilar predictions of shot peening effects even while using an identical combination of Almen intensity and surface coverage. With the fast pace introduction of new generation impact-based surface treatments, there is a need to find a more widespread parameter that would facilitate the direct comparison of all different treatments and relate the main process parameters to the resultant mechanical characteristics. Herein, we propose to use an energy-based parameter to describe the peening process in a more widespread approach, which collectively incorporates the effects of the Almen intensity and surface coverage, as well as the diameter, material, and velocity of the impact media. A set of finite element analyses was developed to demonstrate the correlation of the peening process effects with this energetic approach. Comparisons with the experimental data served as proof of concept, confirming that the proposed method could provide a quite good estimation of the effect of peening parameters on the treated material.