Micro-shot Peening Research Articles

Synergetic effects of micro-shot peening and gas nitriding on the fatigue performance of AISI 4140 steel

Gas-nitriding was performed to enhance the surface hardness and fatigue performance of 4140 steel pre-treated with micro-shot peening (MSP). The 4140 steel was solutionized and tempered at 200 °C/1 h, named as the base metal (BM) with the hardness of 500 HV0.05. Some BM samples were subjected to MSP (i.e., SPBM), and subsequently gas-nitrided at 520 °C/6 h (i.e., NBM). A compound layer of about 10 μm thickness formed on the surface of the NBM sample consisted of nano-grained Fe3N and Fe4N. The NBM sample showed a decline in hardness from the nitrided surface (750 HV0.05) to the matrix (300 HV0.05). In the as-peened condition, the peak residual compressive stress (RCS) was close to −500 MPa, and a very shallow stress field was obtained. After gas-nitriding, the peak RCS decreased to less than −400 MPa, while the affected depth expended to 300 μm. Defects in the compound layer did not deteriorate the fatigue strength/life of the nitrided 4140 steel. The RCS field effectively suppressed fatigue crack initiation and propagation at the surface of the NBM and SPBM samples. By contrast, surface cracks resulted in the fatigue failure of the BM sample.

The oil lubricated fretting wear behavior under different sliding displacements and frequencies of Ti6Al4V titanium alloy as affected by micro-shot peening

The fretting wear behavior under oil lubricants is of great practical significance since oil is usually used to regulate fretting regime for minimizing wear. In this study, micro-shot peening (MSP) was performed on Ti6Al4V titanium alloy, in which 0.6 MPa injection air pressure, 60 s shot time and high-speed steel particles with an average diameter of 50 μm were used. Surface topography, microstructure, hardness and compression residual stress of test samples were examined. Oil lubricated fretting wear tests were then conducted between titanium alloy sample and GCr15 counterbody under different sliding displacements and frequencies. The test results show that the surface structure of MSP treated samples experienced severe plastic deformation, the surface hardness was increased from 310.8 HV to 433.5 HV, and a compression residual stress of −303.5 MPa was introduced within surface layer. Moreover, MSP treatment reduced the coefficients of friction through producing a micro-dimpled surface. Thereby, the fretting wear resistance of MSP treated sample under oil lubricated condition was improved. By comparison, at higher sliding displacement and frequency, the ability of MSP treatment to resist fretting wear was improved more significantly since more better lubricating effect can be obtained. Fretting damage of untreated sample under oil lubrication was mainly attributed to fatigue wear, delamination wear, abrasive wear and oxidation wear, while that of MSP treated sample was mainly regional peeling off and abrasive wear.

Microstructure Evolution and Strengthening Mechanisms of Mg–Steel Welds Subjected to Multiple Microshot Peening Treatment

Microstructure Evolution and Strengthening Mechanisms of Mg–Steel Welds Subjected to Multiple Microshot Peening Treatment

Investigation on Improving the Fretting Wear Properties of Ti6Al4V Alloy via Micro-shot Peening to Produce Surface Asperities and Surface Hardening Layer

Investigation on Improving the Fretting Wear Properties of Ti6Al4V Alloy via Micro-shot Peening to Produce Surface Asperities and Surface Hardening Layer

Correlation between the micro-shot peening coverage and surface microstructural evolution and fluoride-induced corrosion behavior in Monel 400 alloy

This study examines the influence of micro-shot peening (MSP) on Monel 400 alloy, focusing on surface microstructural evolution and fluoride-induced corrosion behavior compared to its solution annealed (SAed) counterpart. MSP treatments were conducted at various surface coverages (100%, 200%, 500%, 1000%, 1500%, and 2000%). Characterization encompassed microhardness, surface roughness, grazing incidence x-ray diffraction (GI-XRD), field emission scanning electron microscopy (FE-SEM) with electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). With increasing the MSP coverage to 2000%, the surface crystallite size decreased from approximately ∼30 µm in the SAed sample to 60 nm. TEM analysis emphasized dislocation slip and formation of dislocation structures as the primary mechanisms for the grain refinement. However, the 2000% coverage exhibited microcrack formation, compromising its hydrofluoric (HF) corrosion resistance. Electrochemical tests revealed severe localized corrosion in all MSP-treated samples except the 1500% coverage, which exhibited a minimum passive current density of 0.2–1.0 µA/cm2. Inductively coupled plasma optical emission spectroscopy (ICP-OES) of immersion solutions showed lower copper and nickel ion concentrations (<150 ppm) in the 1500% MSP-treated sample, indicating its enhanced corrosion resistance. X-ray photoelectron spectroscopy (XPS) identified NiO, NiF2, CuO, CuF2, and Cu(OH)2 phases in SAed and 1500% MSPed samples, with a higher concentration of copper oxide (CuO) in the corrosion film of the 1500% MSP-treated sample, contributing to its superior corrosion resistance.

Mitigating Stress Corrosion Cracking of 304L and 316L Laser Welds in a Salt Spray through Micro-Shot Peening

Two austenitic stainless steel (ASS) plates, 304L and 316L, were cold-rolled (304R and 316R) with a 10% reduction in thickness and then subjected to laser welding. Cold rolling caused slight surface hardening and introduced residual tensile stress into the ASS plates. The susceptibility to stress corrosion cracking (SCC) of the welds (304RW and 316RW) was determined using the U-bend test pieces in a salt spray. To highlight the stress concentration at the weld’s fusion boundary (FB), the top weld reinforcement was not ground off before bending. Moreover, micro-shot peening (MSP) was performed to mitigate the SCC of the welds by imposing high residual compressive stress and forming a fine-grained structure. Cold rolling increased the susceptibility of the 304R specimen to pitting corrosion and intergranular (IG) microcracking. Moreover, pitting corrosion and SCC were found more often at the FBs of the 304RW. The corrosion pits of the peened 304RW (304RWSP) were finer but greater in amount than the those of the un-peened one. The results also indicated that the 316L ASS welds with MSP were resistant to the incidence of pitting corrosion and SCC in a salt spray. The better reliability and longer service life of dry storage canisters could be achieved by using 316L ASS for the construction and application of MSP on it.

Investigation on Surface Characteristic and Tribological Behavior of BS960 Steel by Using Micro-shot Peening and Traditional Shot Peening

Investigation on Surface Characteristic and Tribological Behavior of BS960 Steel by Using Micro-shot Peening and Traditional Shot Peening

Effect of micro-shot peening on microstructure and fluoride-induced corrosion performance of AISI 904L superaustenitic stainless steel

Micro-shot peening (MSP), as an efficient surface engineering technique, is employed to create a severely deformed surface consisting of nanograins on AISI 904L alloy. The fluoride-induced corrosion performance of the micro-shot peened (MSPed) AISI 904L and its solution-annealed counterpart is comparatively investigated using electrochemical techniques, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses. Based on the DC and AC electrochemical measurements, MSPed AISI 904L exhibits a corrosion film with higher resistance and lower passivity current density at the expense of a higher initial corrosion rate. Both samples suffer corrosion in HF solution; however, the solution-annealed one shows deeper and larger localized attacks. The dense distribution of crystallographic defects on the MSPed sample significantly increases the diffusion of alloying elements to the corrosion front. The XPS results reveal that: (i) a corrosion film with a higher contribution of alloying elements (namely, Cr and Mo) is developed on the MSPed one, and more importantly, (ii) its corrosion film contains more oxide compounds and fewer fluorides and hydroxides. A physical model is suggested, and the protection mechanism induced by MSP is discussed.

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

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.

Surface Characteristic and Friction Behavior of Plasma Sprayed FeCoNiCrMo0.2 High Entropy Alloy Coatings on BS960 High-Strength Steel with Subsequent Shot Peening Treatment

The FeCoNiCrMo0.2 high entropy alloy coatings were deposited on BS960 high strength steel by plasma spraying method with four different current intensities (250 A, 350 A, 450 A, 550 A). These coatings were then subjected to a subsequent micro-shot peening treatment. Surface characteristics including surface morphology, microhardness and phase composition were characterized, and the wear resistance of the coatings was assessed by reciprocal friction and wear tests. The results showed that the high entropy alloy coatings had FCC structure. XRD results showed that no new phase was formed during the spraying process. At the same time, shot peening treatment could effectively improve the hardness of the coating surface. Under the four processes, the coating surface prepared with the current intensity of 350 A had the highest microhardness and uniformity before and after shot peening, and the hardness values were 473 ± 10.21 and 504 ± 8.62 HV0.2, respectively. The friction and wear test results showed that the friction coefficients of the four coatings were close to each other at 10 N load, which was about 0.4. When the test load reached 25 N, the friction coefficient of the coating with current intensity of 350 A was lower, and it showed better friction performance. After shot peening, the friction coefficient of the four coatings further decreased to about 0.3 under 10 N loading due to the existence of hardened surface layer. When the test load reached 25 N, the hardened layer would be worn through and the friction coefficient would suddenly rise. Under the 25 N test load, the hardened layer of the high-entropy alloy coating with current intensity of 350 A illustrated better friction resistance.

Influence on Fatigue Strength of Post-Process Treatments on Thin-Walled AlSi10Mg Structures Made by Additive Manufacturing

This work aims to study the fatigue behavior of thin-walled structures and the possible influence of post-process treatments. Specimens with novel geometry were manufactured in AlSi10Mg with different inner diameter values using selective laser melting (SLM) technology and then treated. The different processes applied to the specimens were T6 quenching, microshot peening, and controlled roughness machining. The fracture data were analyzed to obtain the fatigue strength values at 2×106 cycles. The results showed that the mechanical treatments and the T6 quenching improved the fatigue strength by over 55% and over 80%, respectively. Relative density and per cent porosity were measured, and microscopic observations by electron microscope, metallographic microscope, and scanning electron microscope (SEM) were performed. It was possible to conclude that thickness did not affect fatigue life in the studied cases.

Effect of Microshot Peening on Tensile Properties of Water-cooled Stainless Steel

Effect of Microshot Peening on Tensile Properties of Water-cooled Stainless Steel

Effects of Micro-Shot Peening on the Stress Corrosion Cracking of Austenitic Stainless Steel Welds

Micro-shot peening on AISI 304 and 316 stainless steel (SS) laser welds was performed to evaluate its effect on the susceptibility to stress corrosion cracking (SCC) in a salt spray containing 10% NaCl at 80 °C. The cracking susceptibility of the welds was disclosed by testing U-bend specimens in a salt spray. Micro-shot peening caused an intense but narrow deformed layer with a nanocrystal structure and residual compressive stress. Austenite to martensite transformation occurred heavily on the top surface of the micro-shot peened welds. SCC microcracks were more likely to be initiated at the fusion boundary (FB) of the non-peened welds. However, fine pits were formed more easily on the micro-shot peened 304 fusion zone (FZ), which was attributed to the extensive formation of strain-induced martensite. The nanograined structure and induced residual compressive stress in the micro-shot peened layer suppressed microcrack initiation in the 304 and 316 welds in a salt spray. Compared with the other zones in the welds in a salt spray, the high local strain at the FB was the cause of the high cracking susceptibility and could be mitigated by the micro-shot peening treatment.

Surface characteristic and corrosion resistance of different plasma-sprayed coatings (Zn, Al6061and Zn/23Al) on S960 high strength steel with subsequent micro-shot peening

The pure Zn, Al6061 alloy and Zn/23Al coatings were prepared on S960 high strength steel by plasma spraying method respectively, then these coatings were treated with subsequent micro-shot peening. The surface characteristics including surface morphology, micro-hardness, and residual stress were characterized, and the corrosion resistance of the coatings was evaluated by an electro-chemical test, salt spray test and immersion corrosion, respectively. The results showed that the coatings were densified and the surface micro-hardness was improved in the range of HV 20–30 after the micro-shot peening treatment. Taking Al6061 alloy coating as an example, after micro-shot peening, the surface residual stress changed from tensile stress (17 MPa) to compressive stress (−102 MPa). The corrosion testing results showed that the corrosion resistance of Zn coating could be improved by adding Al element and micro-shot peening in the polarization tests. According to EIS results, the impedance of Zn, and Al6061 alloy coatings were improved after micro-shot peening in 3.5 wt% NaCl solution, while the charge transfer resistance of Zn/23Al coating was decreased. In the neutral salt spray test and immersion test, the corrosion resistance of the three coatings was enhanced by micro-shot peening, and the shot-peened Zn/23Al coating illustrated the best corrosion resistance. The improved corrosion resistance of the Zn/23Al coatings can be ascribed to the densification of micro-shot peening and the addition of Al.

Anti-fatigue strengthening mechanism of conventional shot peening and micro-shot peening on bare and micro-arc oxidation coated 6082-T6 aluminum alloy

Conventional shot peening (CSP) and micro-shot peening (MSP) are used to enhance the fatigue property of bare and micro-arc oxidation (MAO) coated 6082-T6 aluminum. The difference in the anti-fatigue strengthening mechanism of CSP and MSP on bare and MAO coated 6082-T6 aluminum alloy is revealed. Results show that MSP provides a more significant improvement in fatigue properties of bare specimens than CSP since the intensely inhibiting effect on crack initiation. Nevertheless, MAO coating impairs the surface integrity of MSP specimens, thus reducing the crack initiating life. In comparison, the effect of deeper affected layer induced by CSP on the improvement of crack propagating life is mostly retained after the MAO process. Hence, for the MAO coated specimen, the CSP prior-treatment is more effective in improving its fatigue property.

Improved fatigue strength of Cr-electroplated 7075-T6 Al alloy by micro-shot peening

The effects of micro-shot peening (MSP) on the rotating bending fatigue resistance of Cr-electroplated AA 7075-T6 Al alloy were investigated. Fe-based amorphous particles with sizes of 50–80 μm were used as the shot balls and peened under 100 % surface coverage. The shot-peen intensity, determined by the height of the N-type Almen specimen, was 0.110 mm. The Cr-electroplated layer consisted of a network of microcracks in the as-plated condition. Without the necessity of micro-crack initiation, the Cr-electroplated substrate had the shortest fatigue life and lowest fatigue strength among the tested samples. MSP significantly increased the fatigue strength/life of 7075-T6 Al alloy with or without Cr-plating. The introduction of high residual compressive stress combined with the formation of a nanograined structure in the MSP zone was responsible for the high resistance to fatigue crack growth of the MSP sample.

Effects of micro-shot peening on the defect tolerance of Al-Si-0.6Mg alloy containing artificial defect

The effects of micro-shot peening (MSP) and artificial surface defects were investigated in relation to the defect tolerance of Al-Si-0.6Mg alloy in the framework of fracture mechanics. The results indicated that coral-shaped casting defects inside the alloy could be effectively quantified using the X-ray synchrotron radiation technique. An affected layer with a surface roughness (Ra) of 1.25 and residual stress of − 125 MPa was introduced on the MSP specimen compared to the un-peened (UP) specimen. The fatigue strengths of the UP and MSP specimens containing the artificial defects decreased as the defect size increased under rotating bending fatigue tests, except in the case of defects with the equivalent size of 395 and 490 µm, respectively. MSP could shift the crack initiation site toward the subsurface, while all the cracks of the specimens with the artificial defects originated from the surface and maintained an aspect ratio of 0.66 during the crack growth process. The relationship between the defect sizes and the fatigue strengths could be reasonably assessed by the modified Kitagawa-Takahashi (K-T) diagrams. The critical defect size of the MSP specimens was increased from 450 to 542 µm compared with that of the UP specimens, owing to the beneficial effect of the compressive residual stress. The defect tolerance of the Al-Si-0.6Mg alloy was improved by the MSP process.

정밀금형용 SKD61 강의 복합표면처리에 의한 표면신뢰성 향상

Purpose: The lifespan of a die-casting steel mold depends on its surface hardness and wear resistance. Gas nitriding treatments for forming surface hardening layers have been widely applied to fabricate reliable die-casting molds. In the present study, we propose a complex surface treatment consisting of a micro-shot peening process and a sulfo-nitriding treatment to improve the surface hardness of SKD61 mold steel.BRMethods: The cross-sectional microstructure of the complex surface-treated SKD61 mold steel was observed using an optical microscope and a scanning electron microscope. The phase of the surface hardening layer was analyzed using an X-ray diffractometer. The micro-hardness and residual stress of the complex surface-treated SKD61 mold steel were evaluated as well.BRResults: The surface hardening layer consisted of the top-most compound layer and a diffusion layer. The micro-shot peening pretreatment increased the thickness of the compound layer. The general nitriding (GN) treatment led to the formation of the FexN compound layer, while the sulfo-nitriding (SN) treatment led to the formation of the FexN and FeS composite compound layer, which was thicker than the compound layer of the GN specimen. The hardness of GN and SN hardening layers improved by 125% and 135%, respectively, relative to that of the as-received SKD61 mold steel with a hardness of 450 HV.BRConclusion: The SN treatment formed a reliable hardening layer with superior hardness than the GN treatment. Furthermore, the thicker sulfo-nitride compound layer produced by the SN treatment can further improve the lifespan of SKD61 steel molds.

Surface characteristics and stress corrosion behavior of AA 7075-T6 aluminum alloys after different shot peening processes

Shot peening is often reported as being beneficial to stress corrosion cracking resistance; however, the increased surface roughness induced by shot peening may promote localized corrosion pitting. Here, AA 7075-T6 aluminum alloys were treated by different shot peening processes, and the surface characteristic, including refined microstructure, residual stress and surface roughness, were characterized, then its effect on localized corrosion pitting and stress crack propagation behavior were investigated. Compared with single shot peening, the microstructure refinement was not further enhanced by dual shot peening with adding a subsequent low intensity of micro-shot peening. The surface residual stress distribution become more uniform, and the average surface residual stress value was increased from −158 MPa to −175 MPa. The maximum residual stress was synchronously increased from −302 MPa to −319 MPa. Meanwhile, the surface roughness (Ra) value was decreased from 4.05 μm to 2.05 μm. Compared with single shot peening, the degree of surface localized corrosion pitting was alleviated after dual shot peening due to its low surface roughness and more uniform compressive residual stress distribution. The depth of stress corrosion cracking for dual shot peening was decreased with a minimum value of 33 μm, which may be ascribed to the high maximum compressive residual stress at the subsurface.

Effect of Micro-Shot Peening on the Fatigue Performance of AISI 304 Stainless Steel

The effects of micro-shot peening on the rotating bending fatigue resistance of AISI 304 stainless steel (SS) were investigated in this study. The strain-hardening, surface roughness and induced residual stress were inspected and correlated with fatigue strength. Micro-shot peening caused intense strain-hardening, phase transformation and residual stress but was also accompanied by a minor increase in surface roughness. A nanograined structure, which was advantageous to fatigue resistance, was observed in the severe shot-peened layer. The absence of microcracks, minor increase in surface roughness, nanograined structure and induced high compressive residual stress in the shot-peened layer were responsible for the improved fatigue strength of AISI 304 SS.