Ultrasonic Shot Peening Treatment Research Articles

Effect of Ultrasonic Shot Peening on Microstructure and Corrosion Properties of GTA-Welded 304L Stainless Steel

Austenitic stainless steels used in structural applications suffer from stress corrosion cracking due to residual stresses during welding. Much research is being conducted to prevent the stress corrosion cracking of austenitic steels by inducing compressive residual stresses. One method is ultrasonic shot peening (USP), which is used to apply compressive stress by modifying the mechanical properties of the material’s surface. In this study, 304L stainless steel was butt-welded by gas tungsten arc welding (GTAW) and subsequently subjected to compressive residual stress to a depth of 1 mm from the surface by a USP treatment. The influence of USP on microstructural changes in the base metal, the HAZ and weldment, and the corrosion properties was analyzed. A microstructural analysis was conducted using SEM-EDS, XRD, and EBSD methods alongside residual stress measurements. The surface and cross-sectional corrosion behavior was evaluated and analyzed using a potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS) measurements, a double-loop electrochemical potentiokinetic reactivation (DL-EPR) test, and an ASTM A262 Pr. C test. The surface was deformed and roughened by the USP. The deformed areas formed crevices, and the inside of the crevices contained some cracks. The crevices and internal cracks caused pitting, which reduced the resistance of the passivation film. The cross-section was subjected to compressive residual stress to a depth of 1 mm from the surface, and the outermost area of the cross-section had fine grain refinement, forming a solid passivation film that improved the corrosion resistance.

Effect of surface strengthening by ultrasonic shot peening on TC17 alloy

This paper investigates the effects of ultrasonic shot peening (USP) on surface morphology, microstructure, and residual stress field distribution of TC17 alloy under different process parameters. The aim is to reveal the surface strengthening mechanism of TC17 alloy caused by USP. The results suggest that the use of the 2.5 mm projectile diameter leads to an increase in surface roughness, plastic deformation, and a deeper grain refinement layer compared to the 1.5 mm projectile diameter. Additionally, it results in a greater depth of the compressive residual stress layer and maximum compressive residual stress. The crack initiation sites under two projectile diameters are located below the compressive residual stress layer. The USP treatment introduces compressive residual stress on the surface, inhibiting the initiation of surface cracks, and the deeper compressive residual stress layer offsets the early fatigue failure caused by higher roughness.

Ultrastrong gradient M50 bearing steel with lath-shape nano-martensite by ultrasonic shot peening and its enhanced wear resistance at elevated temperature

This investigation delves into the intricacies of the process mechanism for generating a gradient nanostructured surface (GNS) layer on M50 bearing steel, with the aim of augmenting its surface hardness and wear resistance under elevated temperature. The electron backscatter diffraction and transmission electron microscopy substantiate the successful formation of a GNS layer, surpassing 200 µm in thickness, on the M50 bearing steel treated by Ultrasonic shot peening (USP) technology. The severe plastic deformation (SPD) induced by the USP process resulted in a significant refinement of the martensite in M50 bearing steel, leading to a remarkable 32.25 % increase in surface hardness compared to its untreated coarse-grained (CG) counterpart. Pin-on-Disk wear tests were conducted at an elevated temperature of 300 °C on both the as-received CG-M50 and USP-treated M50 bearing steel samples to evaluate the impact of USP treatment on the wear resistance of M50 bearing steel. Experimental results reveal that the volume loss of the USP-treated M50 bearing steel is 94.9 % less than that of the untreated CG-M50 bearing steel after 4 h of wear tests. The improved wear resistance of the USP-treated M50 bearing steel can be attributed to the creation of an ultrastrong and stable GNS layer facilitated by USP.

Effect of surface contamination on electrochemical corrosion behavior of ultrasonic shot peened TA2 alloy

Ultrasonic shot peening (USSP) is a technique to tune the performance of metallic materials by generating gradient nanocrystalline structure (GNS) as well as residual compressive stress. However, surface contamination can also be introduced during USSP. The nature of this surface contamination layer and how it influences the corrosion behavior of alloy require further investigation. In this work, we found that a Fe-rich oxide layer with a thickness of around 50 nm, mainly in an amorphous state, was introduced on the topmost surface layer of TA2 alloy during USSP treatment. Electrochemical corrosion results indicate that this Fe-rich oxide significantly decreases the corrosion resistance of TA2 alloy. By polishing off this surface contamination layer, the corrosion resistance of the peened sample becomes superior compared to the untreated counterpart, indicating that the introduction of the Fe-rich oxide layer conceals the beneficial effect of GNS caused by USSP. Additionally, the corrosion resistance of TA2 alloy after USSP treatment exhibits a downward trend with the increasing repeated use of steel shots. The corrosion mechanism and potential use of this surface contamination layer are also briefly discussed.

A comparative assessment of the effects of laser shock peening and ultrasonic shot peening on surface integrity and ratcheting fatigue performance of HSLA steel

In this work, a comparative assessment of the effects of laser shock peening (LSP) and ultrasonic shot peening (USP) on surface integrity and ratcheting fatigue performance of ASTM A588 Grade D high strength low alloy steel was done. Surface roughness, microhardness, microstructure, residual stress, and micro-texture analyses were used to describe the unpeened and peened surfaces. Three sets of tension-compression asymmetric cyclic loading tests were carried out at room temperature on unpeened and peened specimens to evaluate the effects of the applied treatment on strain accumulation and fatigue life. The quantitative dislocation densities of selected specimens were calculated in order to examine the mechanism underlying the softening behavior of USP-treated specimens during fatigue testing. The results are presented in light of the substantial surface roughness, lower compressive residual stress, and weakening of texture intensity revealing an unexpectedly large drop in fatigue strength following USP treatment compared to the unpeened and laser-peened specimens.

Ultrastrong gradient nanostructured CSS-42L bearing steel and its enhanced wear resistance at elevated temperature

A gradient nanostructured surface layer was successfully fabricated on the CSS-42L(15Cr14Co12Mo5Ni) aerospace bearing steel by ultrasonic shot peening (USP) technology at room temperature. The original austenite in the as-received (AR) CSS-42L bearing steel was fully transferred into lath martensite by quenching and two cryogenic tempering cycles. The lath martensitic structure at the surface of the bearing steel was refined into nanoscale martensite phases with an average size of 33.9 nm after USP treatment. The microhardness of the gradient heterogeneous nanostructured CSS-42L bearing steel increased by approximately 39 % compared to that of the tempered bearing steel. The mechanisms of martensite refinement during the USP process were analyzed and discussed using advanced materials characterization methods. Dry sliding wear tests at elevated temperatures (500 °C) were conducted on the tempered and USPed CSS-42L bearing steel samples, respectively. The wear resistance of the USPed sample was significantly enhanced compared to that of its untreated coarse-grained counterpart. The wear rate coefficient of the USPed CSS-42L was reduced by 80.42 % compared to the AR sample. The superior wear resistance of the USPed CSS-42L bearing steel was attributed to the formation of an ultrastrong surface layer with a gradient heterogeneous nanostructure fabricated by USP technology.

Understanding the recrystallization and phase transformation of gradient nanostructured M50 steel under the athermal effect of electrical pulses

M50 steel is a commonly used material for aeroengine main shaft bearings. In this study, a gradient nanostructured M50 steel was fabricated by an efficient surface nanocrystallization method, i.e., ultrasonic shot peening (USP) technology. The recrystallization behavior and phase transformation of gradient nanostructured M50 steel under the athermal effect of electrical pulses were investigated. Compared with the USPed sample, the ferrite structure size was 32.5% smaller, and the structure size uniformity was 51.5% greater in the 0–50 μm region after USP treatment and electrical pulsing treatment (EPT) with 38 A/mm2–1 s. Athermally induced ferrite recrystallization by EPT accompanied with obvious precipitation of VC and Mo2C carbides, and decomposition of austenite occurred during ferrite structure coarsening. EPT has different responses to different depths of gradient M50 steel, and there is an optimal current density to achieve structure refinement in different depths. However, the coarse-grain tempered M50 steel did not undergo obvious ferrite structure refinement under the same EPT parameters. The results revealed that the EPT promoted static recrystallization of incompletely recrystallized structures after USP processing by activating the release of stored deformation energy. Static recrystallization under the athermal effect of EPT was achieved by promoting the migration of the subgrain boundary to absorb the surrounding dislocations and increase the misorientation between itself and the surrounding ferrite structure. The mechanism of the athermal effect of EPT was based on electron-defect interactions, such as dislocations and lattice distortions. High-density nonequilibrium grain boundaries, acting as “active sites”, accelerating the process of recrystallization under the effect of electric pulses. This study proposed a method for optimizing EPT parameters through the change in instantaneous resistance to evaluate the degree of recrystallization of the gradient structure.

Enhanced Tribological Properties of CrN Coatings on Densified Surfaces of Fe-Based Porous Materials Obtained Through Powder Metallurgy and Ultrasonic Shot Peening Treatment

Enhanced Tribological Properties of CrN Coatings on Densified Surfaces of Fe-Based Porous Materials Obtained Through Powder Metallurgy and Ultrasonic Shot Peening Treatment

Nanostructure evolution of reticular nano-TiB whiskers reinforced titanium matrix composite subjected to ultrasonic shot peening

Titanium matrix composites (TMCs) have drawn widespread attention because of their superior mechanical properties. In this study, nano-TiB whiskers reinforced TMC was fabricated using a direct laser deposition technique and then subjected to ultrasonic shot peening (USP) for different durations. The microstructure characterization results indicated that the surface grain refinement of αTi was dominated by complicated dislocation motion. The primary grain refinement mode during the microstructure evolution was the transverse splitting of the elongated lamellae. By interacting with dislocations, the TiB whiskers facilitated the evolution of nanostructures. After USP treatment, TiBw exhibited obvious fractures, but the TiB-Ti interface remained sharp and clear, showing excellent interfacial properties. The use of USP resulted in a significant compressive residual stress field, which increased with peening time. Surface hardness also increased as a result of fine grain and strain strengthening. When compared to the initial sample, the maximum microhardness of the sample after USP treatment increased by 48%.

Influence of ultrasonic shot peening on the microstructure and impression creep performance of squeeze-cast AZ91 alloy reinforced with graphene nanoplatelets

The present investigation explores the influence of graphene nanoplatelets (GNPs) (0.5, 1.0, and 2.0 wt %) addition as well as ultrasonic shot peening (USP) for 10, 20, and 30 s on the microstructure, hardness, and impression creep response of AZ91 alloy fabricated by squeeze-casting for transmission housing applications. The as-cast AZ91-xGNPs nanocomposites displays lower grain size, lesser Mg17Al12 phase fraction, and higher dislocation density. The USP technique induces compressive residual stress (CRS) and high strain hardening at the surface followed by high dislocation density that increases with time. Both surface roughness as well as the dimple size and thickness after USP treatment are lower for the nanocomposites than for the AZ91. The hardness and creep resistance of the as-cast AZ91-xGNPs nanocomposites are superior to the monolithic alloy, which further improved after USP treatment. In contrast to the base alloy, the GNC3 nanocomposite displays the best hardness and impression creep resistance both in the as-cast and USP-treated condition. Dislocation climb regulated by pipe diffusion is the dominating creep mechanism in the as-cast and USP-treated materials. The improvement of impression creep performance for as-cast nanocomposites is attributed to the reduced Mg17Al12 phase content, high dislocation density, and strengthening from the GNPs. In contrast, the superior creep performance of USP-treated nanocomposites is attributed to the presence of CRS along with high dislocation density and work hardening on the surface.

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

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.

Effect of ultrasonic shot peening duration on the microstructure and mechanical properties of CrMnFeCoNi high-entropy alloy

In this work, ultrasonic shot peening (USP) was performed for a CrMnFeCoNi high-entropy alloy with an equal atomic ratio to improve the mechanical performance at room temperature. The microstructure evolution and mechanical properties of the CrMnFeCoNi high-entropy alloy under different USP durations were studied. The effects of USP-induced grain refinement, phase transformation, strengthening, and fracture morphologies were analyzed. The results indicated that a certain thickness of compressive residual stress layer with nanocrystalline was formed on the surface of the alloy. After USP, the phase was transformed from the FCC phase to the mixed dual phases FCC+BCC. The alloy exhibited a strength-ductility balance, with hardness and strength enhanced significantly, while elongation to failure remained at around 30%. Additionally, the sample before USP exhibited a typical ductile fracture, while after USP, it was transformed into a mixed fracture of dimple and quasi-cleavage or cleavage. The crack initiated from the sub-surface rather than the initial surface, and then propagated to the interior structure after coming into contact with the surface strengthening layer, effectively delaying the failure of the material. It was demonstrated that the ultrasonic shot peening treatment is a general and efficient physical strengthening method for high-entropy alloy at room temperature.

Effects of ultrasonic shot peening on fatigue behavior of TA15 titanium alloy fabricated by laser melting deposition

Due to the influence of tensile residual stress and pores, the fatigue resistance of titanium alloy fabricated by laser melting deposition (LMD) still needs to be improved. In this study, ultrasonic shot peening (USP) was utilized to strengthen the TA15 titanium alloy manufactured by LMD. The surface topography, microstructure, microhardness, residual stress and fatigue behavior were analyzed. After USP treatment, the root-mean-square deviation of the three-dimensional profile (Sq) and the local stress concentration factor (Kst) increased. High-density dislocations (dislocation tangles, dislocation walls, dislocation cells) and deformation twins were generated on the specimen subsurface. The existence of high-density dislocations improved the surface microhardness. Meanwhile, changes in microstructure affected the state and distribution of residual stress. The surface tensile residual stress was completely transformed into compressive residual stress. The fatigue behavior was significantly influenced. Under 720 MPa and 760 MPa stress levels, the safe fatigue life (reliability R = 0.95, confidence level C = 0.95) of TA15 titanium alloy manufactured by LMD increased by 200 % and 43 %, respectively. In the pore-profile valley competition, the pore showed greater fatigue sensitivity. The high-density dislocations and compressive residual stress accounted for the improvement in fatigue life. The high-density dislocations hindered the crack nucleation and short crack propagation at pores near the surface. The compressive residual stress reduced the crack propagation rate in the stable crack propagation stage. The results indicated USP as an effective method to improve the fatigue performance of the TA15 titanium alloy manufactured by LMD.

Residual stress and microhardness evolution induced by conventional and ultrasonic shot peening

Very limited comparative research has been conducted on microstructure evolution induced by different peening methods. Herein, the 2024T351 aluminium alloy was subjected to conventional shot peening (CSP) and ultrasonic shot peening (USP) under the identical Almen height to investigate the differences in surface roughness, residual stress and microhardness. The results demonstrated that under the same Almen height, the CSP treatment resulted in a rougher surface with higher surface roughness and more surface defects, and higher surface and maximum compressive residual stress (CRS) than the USP treatment. In contrast, the CRS depth was relatively lower for the CSP treated samples. In addition, the USP treatment produced more significant microhardness and hardened layer than the CSP treatment.

Enhanced Wear Resistance of the Ultrastrong Ultrasonic Shot-Peened M50 Bearing Steel with Gradient Nanograins

The enhancement of the wear resistance has long been important for bearing steels, hampered in part by the lack of suitable surface strengthening techniques. In this study, ultrasonic shot peening (USP) is employed to enhance the wear resistance of the M50 bearing steel by generating an ultrastrong surface layer with gradient nanograins. The effects of USP treatment on the surface integrity, microstructures, and wear behavior of M50 steel are investigated. The microstructural observation shows that the gradient nanograined surface layer is over 200 μm thick. The lath martensite is refined to nano-martensitic subgrains with few low angle boundaries in the USP-treated M50 steel. Additionally, the microhardness of the nanostructured M50 steel is increased from 795 HV to 987 HV with a penetrating depth of around 800 μm. Wear tests show that the wear rate of the USP-treated M50 steel is reduced by 50.4% under sliding conditions compared to that of the untreated samples. The significantly enhanced wear resistance of the USP-treated M50 is attributed to the ultrastrong gradient nanograined surface layer. The wear mechanism of the USP-treated M50 steel changes from oxidative wear and severe plowing wear to mild plowing wear. Additionally, the thickness of the plastic deformation layer generated during the friction process is reduced. This work provides the materials scientists and engineers with an efficient surface treatment method to enhance the wear resistance of high-strength steels.

Nanoscale corrosion investigation of surface nanocrystallized 7150 Al alloy in 3.5 wt% NaCl solution by using FIB-TEM techniques

Nanocrystalline grains were fabricated on the surface layer of 7150 Al alloy by using ultrasonic shot peening treatment. The nanoscale corrosion behavior of this surface nanocrystallized 7150 Al alloy in 3.5 wt% NaCl solution was studied by combining focused ion beam (FIB) and transmission electron microscopy (TEM) techniques. It was found that, compared with the untreated substrate alloy, pit corrosion is largely inhibited and intergranular corrosion (IGC) is eliminated on the surface nanocrystallized layer. The transition from IGC to uniform corrosion caused by ultrasonic shot peening can be attributed to the disappearance of precipitate free zone (PFZ) along grain boundaries.

The influence of ultrasonic shot peening on the surface roughness, microstructure, and mechanical properties of TC2 thin-sheet

The research aimed to find a physical strengthening method for thin-sheet metal parts using an ultrasonic shot peening (USP) method at room temperature. Herein, the influence of the USP treatments on the surface roughness, microstructure, micro-hardness, and tensile strength of the TC2 thin-sheet with a thickness of 0.5 mm was investigated systematically. The results showed that the Ra of the TC2 thin-sheets increased to 0.374, 0.418 and 0.479 μm after the USP treatments with the intensities of 0.189, 0.277 and 0.360 mmA, respectively. Compared with pneumatic shot peening (PSP) of similar Almen intensity, the surface quality of the alloy after USP treatment was significantly improved. The cross-sectional micro-hardness curves of the USP-treated TC2 thin-sheet showed ‘V’ shapes, and the micro-hardness of the surface layer increased as the shot peening intensity increased. When the Almen intensity was 0.360 mmA, the corresponding maximum micro-hardness of the surface layer was 362.9 HV0.025, which was 67.9 HV0.025 larger than that of the initial alloy. The USP treatment also improved the tensile strength of the TC2 thin-sheet, and the tensile strength increased as the shot peening intensity increased. When the Almen intensity was 0.360 mmA, the tensile strength was increased by about 6.23%, reaching 799.3 MPa. Therefore, the USP treatment method is a potential physical strengthening method for thin-walled parts at room temperature.

Characteristics of friction and wear of Al-Zn-Mg-Cu alloy after application of ultrasonic shot peening technology

7A52 aluminum alloys were treated by ultrasonic shot peening (USSP) technology. Then, friction and wear behavior of 7A52 aluminum alloys was obtained by a ball-on-disk friction and wear test. The surface grains of the 7A52 aluminum alloys were refined into nanocrystals with an average size of about 23 nm, and a severe plastic deformation zone with a thickness of about 100 μm was produced by USSP treatment. Compared with the un-USSP specimen, the coefficient of friction (COF) values of the USSP-treated specimen were obviously decreased by 18.04%, 9.09%, 8.67%, 15.79% under the friction load of 5 N, 10 N, 30 N and 50 N. As the wear load increases, the specimens before and after treatment show different wear mechanisms.

Enhanced corrosion resistance of the surface modified Ti-13Nb-13Zr alloy by ultrasonic shot peening

The near-β Ti-13Nb-13Zr alloy was processed by ultrasonic shot peening (USSP) for different durations of 15–120 s to develop surface nanostructure. The effect of the USSP was studied on its corrosion behaviour in Ringer's solution, by electrochemical impedance spectroscopy and potentiodynamic polarization tests. The electrochemical study revealed reduction in corrosion of the USSP treated samples. There was maximum passivation in the 30 s of USSP treatment, while it decreased with an increase in USSP duration. The improvement in the corrosion resistance from USSP was due to grain refinement and the associated compressive residual stresses in the surface region.

Effect of ultrasonic shot peening on microstructure evolution and corrosion resistance of selective laser melted Ti–6Al–4V alloy

The ultrasonic shot peening (USP) treatment was adopted to improve the compressive residual stress, microhardness and corrosion resistance of Ti–6Al–4V (TC4) titanium alloy fabricated by selective laser melting (SLM). The optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and hardness test were used to investigate the microstructure evolution. The effect of the USP on electrochemical behaviour of the SLM TC4 alloy in a 3.5 wt. % NaCl solution was studied using potentiodynamic polarization. After USP treatment, compressive residual stress was induced and microhardness significantly increased. Proper USP treatment can effectively improve corrosion resistance of the SLM TC4 alloy, which is manifested by the increase in corrosion potential and decrease in corrosion current density.