Shot Peened Surface Research Articles

Influence of Ultrasonic Surface Rolling Process and Shot Peening on Fretting Fatigue Performance of Ti-6Al-4V

At present, there are many studies on the residual stress field and plastic strain field introduced by surface strengthening, which can well hinder the initiation of early fatigue cracks and delay the propagation of fatigue cracks. However, there are few studies on the effects of these key factors on fretting wear. In the paper, shot-peening (SP) and ultrasonic surface rolling process (USRP) were performed on Ti-6Al-4V plate specimens. The surface hardness and residual stresses of the material were tested by vickers indenter and X-ray diffraction residual stress analyzer. Microhardness were measured by HXD-1000MC/CD micro Vickers hardness tester. The effects of different surface strengthening on its fretting fatigue properties were verified by fretting fatigue experiments. The fretting fatigue fracture surface and wear morphology of the specimens were studied and analyzed by means of microscopic observation, and the mechanism of improving fretting fatigue life by surface strengthening process was further explained. After USRP treatment, the surface roughness of Ti-6Al-4V is significantly improved. In addition, the microhardness of the specimen after SP reaches the maximum at 80 μm from the surface, which is about 123% higher than that of the AsR specimen. After USRP, it reaches the maximum at 150 μm from the surface, which is about 128% higher than that of AsR specimen. It is also found that the residual compressive stress of the specimens treated by USRP and SP increases first and then decreases with the depth direction, and the residual stress reaches the maximum on the sub surface. The USRP specimen reaches the maximum value at 0.18 mm, about − 550 MPa, while the SP specimen reaches the maximum value at 0.1 mm, about − 380 MPa. The fretting fatigue life of Ti-6Al-4V effectively improved after USRP and SP. The surface integrity of specimens after USRP is the best, which has deeper residual compressive stress layer and more refined grain. In this paper, a fretting wear device is designed to carry out fretting fatigue experiments on specimens with different surface strengthening.

Fatigue behaviour of PBF additive manufactured TI6AL4V alloy after shot and laser peening

Additive manufacturing (AM) of metallic parts is a relatively new manufacturing procedure. Many industry sectors, such as the aerospace or automotive sectors, have started to apply this technology to produce some elements, thus reducing costs and weight. Several metallic alloys have been employed for AM. Due to the high strength-to-density ratio, Ti6Al4V alloy is probably the alloy most used for AM in the aerospace industry. This alloy usually shows good static strength properties. However, the presence of internal defects and the surface roughness result in a fatigue strength that is clearly lower than that of materials produced by traditional processes. Moreover, the scatter of the fatigue results is generally higher than in the case of wrought pieces.Different treatments have been proposed to improve the fatigue behavior by reducing internal defects and roughness or generating a favorable residual stress field. In this work, selected surface treatments were considered to improve the fatigue strength of AM parts, including shot and laser peening as well as a combination of shot peening plus chemical assisted surface enhancement (CASE®). Three groups of specimens, each with one of the surface treatments, were fatigue tested to compare the results produced by these treatments. The residual stresses, roughness and hardness produced by the treatments were analyzed. After testing, the fracture surfaces were also analyzed to better understand the fatigue process of the different groups of specimens. The results indicate that laser peening produced the best results, followed by shot peening plus CASE and shot peening. In all three cases, the fatigue strength was much higher than that of the reference group without surface treatment. It was also observed that all failures initiated from an interior defect in the shot peening plus CASE group, four out of six failures in the laser peened group, but only one failure in the case of shot peened group and none in the reference group. Failures of specimens with initiation from internal defects started from defects located deeper than the compressive residual stress layer produced by the treatments.

Numerical modeling and experimental verification of surface roughness of 12Cr2Ni4A alloy steel generated by shot peening

Shot peening produces a high-speed shot flow acting on the sprayed surface, which not only produces residual compressive stress, but also changes the microstructure of the rough surface of the parts. Surface roughness affects the fatigue strength of the parts. In order to study the influence of shot peening time on the surface morphology of 12Cr2Ni4A alloy steel, the number of craters and the shot diameter are measured under the given peening parameters. A random multiple-shot model is established with ABAQUS to obtain the rough surface profile under the peening parameters, and the rough surface profile is processed by Gaussian filtering to calculate the roughness of the shot peening surface. The results show that the numerical calculation value of the shot peening surface roughness proposed in the paper is highly consistent with the experimental measurement value. Based on the calculation model of the rough surface, this paper analyzes the relationship between different roughness parameters and shot peening time, and investigates the influence of initial surface roughness on the surface morphology after shot peening. This paper provides a new idea for calculating and predicting rough surface in shot peening process . • A numerical simulation model based on experiments is developed to study surface roughness of shot peening. • Roughness parameters are calculated based on the profile in the simulation processed by Gaussian filtering. • Based on the simulation model, the relationship between different roughness parameters and shot peening time is analyzed. • The influence of initial surface roughness on the surface morphology after shot peening is discussed.

Surface Shot Peening Post-processing of Inconel 718 Alloy Parts Printed by Laser Powder Bed Fusion Additive Manufacturing

Surface Shot Peening Post-processing of Inconel 718 Alloy Parts Printed by Laser Powder Bed Fusion Additive Manufacturing

Effect of High-Energy Shot Peening on Surface Nanocrystallization and Integrity of AISI 4140 Steel: A Numerical and Experimental Investigation

High-energy shot peening (HESP) can introduce not only compressive residual stresses but also nanocrystalline layer close to the surface. Surface nanocrystallization leads to great improvement of surface hardness and fatigue property of treated metallic components. In this paper, a finite element method (FEM) was proposed to investigate the effects of HESP parameters, including surface coverage, shot diameter and shot velocity, on the grain refinement phenomenon. The quantitative relationship between the grain size and the equivalent plastic strain (PEEQ) was obtained by comparing the data from FEM simulation and x-ray diffraction in experiments. The surface topography and the depth profiles of microhardness and full width at half maximum were analyzed with the aim of assessing and verifying the surface integrity and nanostructure formation after HESP treatment. The results showed that appropriate increment of surface coverage, shot diameter and shot velocity was beneficial to grain refinement and nanostructure formation on a treated surface after HESP treatment. Through reasonable process control of HESP, microcracks did not appear on a treated surface even when the shot peening surface coverage reached up to 1000%.

Fatigue study on AISI/SAE 1015 steel with shot peening under corrosive environments

This work evaluates alternative four-point bending fatigue stress in 2 < pH < 4 corrosive media of AISI/SAE 1015 steel subjected to shot peening surface treatment. A tri factorial experimental design with replications was used. The intervening factors were: i) load levels, 0.96, 0.85, 0.73, 0.65; ii) corrosive media; pH2, pH4, ambient; iii) shot-peening surface treatment; without any shot peening, S230 shot peening and CW-41 shot peening, for which a total of 108 specimens were tested with a reliability level of 95% and a probability of failure of 3%. Tests were performed on a universal machine in a three-point bending assembly with an electro-pneumatic system. The cycle counting and control were performed by a programmable logic controller. The results of the stress-life method in each one of the scenarios show that the best condition was shown in the probes with shot peening S230 and CW-41 treatment under atmospheric conditions, where the material tends to increase its fatigue behavior; the number of cycles reached 36990 and 37773 respectively. The corrosive effect of pH2 and pH4 reduced on probes without shot peening treatment with a maximum of 9862 and 8670 cycles respectively; however, for S230 and CW-41 shots, an increase in cycle number in pH2 and pH4 was evidenced, with the best result for S230 shot at pH4 with a maximum range of 21568. Likewise, the fractography analysis shows mixed fractures with fatigue failure mechanism; the characteristics found were beach marks, secondary cracks, localized oxidation (filiform, plates, pitting, stress, and compression corrosion), nucleation, microvoids, cleavage facets, intergranular and transgranular cracks.

Study on Shot peening Coverage of Metal Surface Based on Deep Learning

The surface shot peening coverage of industrial parts will affect the performance of the parts. Therefore, it is of great significance for the identification of the metal surface shot peening coverage area and the uncovered area for the metallurgical process. This paper uses the idea of image semantic segmentation, using CCD industrial camera to select and shoot the metal surface of 67%,89% and 98% shot peening coverage. Based on UNet and UNet++ model, the shot peening area is segmented. After training 200 epoch, the network converges and the training accuracy can reach 98.45%. Comparing the two kinds of network training results, using the UNet++ model with good results to predict the selected 18 metal surfaces, the proportion of shot peening coverage area and uncovered area is counted, and then the K-means clustering algorithm is used to classify. The classification accuracy can reach 100%.

Cumulative Fatigue damage of AA7075-T6 under Shot Peening and Ultrasonic Surface Treatments

One of the important aspects of mechanical design is improving fatigue life.; In this work, the effect of Ultrasonic impact treatment (UIP) and shot peening (SP)on constant cumulative fatigue life and fatigue strength of AA7075-T6 were studied; The sample group was machined and primed, and some specimens were treated using ultrasonic impact therapy (UIT) with one line of peening. Fatigue experiments were conducted under constant and variable amplitude (R=-1) at ambient temperature to determine the fatigue life of the S-N curve and fatigue strength during treatment 3.46% and 8.57% at 107 cycles for (UIT) and (SP). Cumulative fatigue damage testing was carried out for two steps loading it is observed that the fatigue life for SP and UIP treated specimens was improved compared to the unpeeled results. The fatigue endurance limit was enhanced by 35% for UIT and 54% for SP. The fatigue life for both treatments was much improved compared to as-received metal. These results also show a strong tendency of increasing fatigue strength after application of (UIT) and (SP) with an increase in mechanical properties of the material used.

Effect of shot peening on augmenting the thermo-fluid characteristic of a concentric tube water-to-air counter flow heat exchanger

The current work focuses on heat transfer and pressure drop performance and determines the thermal enhancement factor in a concentric tube heat exchanger (HEX), whereby the external profile of the copper inner tube is modified via shot peening. The Reynolds number of the water-side varied from 6000 to 12,000 and the water temperature varied from 60 to 80 °C. The cold air mass flow rate was maintained at approximately 0.01 kg/s. The Nusselt number of a shot-peened surface HEX was improved by nearly 25.78%, compared with the normal copper tube HEX, where the water inlet temperature and Re were 80 °C and 10,000, respectively. The test outcomes displayed that the increase in surface roughness induces the rise in HTFs turbulence and, successively, an augmentation of Nusselt number. The shot peening process breaks the thickness of the viscid sublayer and it creates the local wall turbulence owing to flow separation and reattachment between the grain particles, which enhances the heat transfer to a considerable amount. The friction factor increased up to 26.82% when Re was 6000 and reduced as Re increased. The thermal enhancement factors were in the range 1.007–1.19 for surface roughness of 6.41 μm.

Effects of shot peening and artificial surface defects on fatigue properties of 50CrV4 steel

Shot peening processes are commonly used for improving the fatigue properties of steels. Shot peening introduces a compressive residual stress field in the near surface of steel, which can reduce or stop the growth of fatigue cracks and improve fatigue properties. This study experimentally investigated the effect of shot peening on the fatigue properties of 50CrV4 steel alloys with different artificial surface defects. Drilling tools were used to introduce different artificial defects with root radii of 0.585 mm and 0.895 mm on the surface of unpeened samples. The shot peening was applied to the drilled and undrilled samples. Scanning electron microscopy (SEM) observations, micro-hardness and X-ray diffraction residual stress measurements were conducted to analyse the characteristics of the shot-peened and unpeened samples. The results show that the shot peening leads to the transformation of the retained austenite to martensite in the near-surface microstructure. The hardness rates of the surface and near surface both increase by 8% after the shot peening. The peened samples exhibit compressive residual stresses with a high degree of isotropy in the near surface. The fatigue properties of samples were experimentally evaluated by conducting 3-point bending tests. The results indicate that the shot peening improves the fatigue life of drilled and undrilled samples. For the defects with the root radius of 0.895 mm, the shot peening leads to a 500% improvement in the fatigue life compared to unpeened samples regardless of defect depth. For the defects with the root radius of 0.585 mm, the improvement in fatigue life is 40% for the defect depth of 0.2 mm compared to unpeened samples. The improvement increases to 60% and 200% by increasing the defect depths to 0.4 mm and 0.6 mm. The fatigue properties are linked to the changes in the features of defects mainly caused by the deformation hardening and compressive residual stress after shot peening.

The Influence of Surface Shot Peening on the Isothermal Oxidation Behavior of NiCrAlYSi Coating

The Influence of Surface Shot Peening on the Isothermal Oxidation Behavior of NiCrAlYSi Coating

A study on pre-treatment with rotation accelerated shot peening in multi-NbN films by double glow plasma surface metallurgy

Multi-NbN films manufactured by a hybrid process comprising pre-treatment rotation accelerated shot peening (RASP) and double glow plasma surface metallurgy (DG technique) and designed to protect titanium alloys were assessed to determine their tribological and mechanical properties. The surface microstructures of a modified TA15 alloy were characterized using X-ray diffraction, scanning electron microscopy, 3D-profilometer and micro-Vickers hardness testing. The results reveal that the distribution of N concentration on layers was influenced by the pre-treatment with RASP, in which a dense nitride gradient layer was formed inside the films and a new phase β-Nb2N occurred at the film surface. This is because a large number of defects on the surface layer were generated by the pre-treatment with RASP. While multi-NbN films on the original sample without new phase detected can be divided into three zones—NbTi interdiffusion layer, Nb-Ti-N interdiffusion layer, and NbN layer. Strong increase in surface hardness was verified in correspondence of elevated peening velocity, and the hardest RASP-60 m/s sample is up to 30.1803 GPa. However, the thickness of films cannot keep increasing trend in agreement with increasing shot peeing velocity. The thickest films occurred on the RASP-40 m/s sample, is 5.85 μm. The results show that the RASP-treated samples exhibited more serious damage than the untreated sample, due to the formation of β-Nb2N phase with brittle structure which bonding on the course surface are incapable of overcoming the damage of shearing stress from counterparts. And once starting to crack, the films that are supposed to protect the substrate are turned into hard abrasive particles that adversely affect the wear resistance of the substrate.

Effects of constrained groove pressing, severe shot peening and ultrasonic nanocrystal surface modification on microstructure and mechanical behavior of S500MC high strength low alloy automotive steel

S500MC high strength low alloy automotive steel is exposed to bulk severe plastic deformation (SPD) via constrained groove pressing (CGP) and surface severe plastic deformation (S2PD) via severe shot peening (SSP) and ultrasonic nanocrystal surface modification (UNSM). SSP and UNSM could create a nanocrystallization layer till 50–100 µm away from outmost surface. EBSD investigations showed average nano-grain size obtained via SSP and UNSM was found to be below 100 nm regime. The strength was improved via 1st to 4th pass of CGP, but elongation percentage decreased abruptly. UNSM achieves both strength-ductility improvement with gradient structure. SSP improves the total elongation however a slight decrease on strength is observed. SSP and UNSM showed better wear and friction resistance particularly at lower loads compared to CGP and untreated specimens. Nevertheless, wear and friction behavior at higher loads showed better responses for Bulk-SPD applications regardless of pass numbers. The frictional load increase played a detrimental role in removing a nanocrystallization surface layer and diminishing the positive influence of SSP and UNSM.

Effect of shot-peening on the passive film formation and corrosion of carbon steel in LiBr aqueous solution

In absorption chillers using LiBr aqueous solution, corrosion problems of carbon steel heat exchangers become more serious as the temperature of the generator increases. To reduce the corrosion problems, various surface treatment methods are applied such as a shot-peening. In this study, corrosion characteristics were investigated for untreated and shot-peened surfaces. Pyrex tube samples containing the specimens and LiBr aqueous solution with Li2MoO4 were made and put into a high temperature oven at 200 °C After 2000 hours, the surface and cross section of carbon steel specimens were observed using field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDS). It was found that the passive films have the characteristic of a double layer consisting of a thick MoO2 layer and thin Fe3O4 layer. Thicker passive films were observed on the shot-peened surface than the untreated one. As a result of corrosion depth measurement, the shot-peened specimens showed a slightly smaller uniform corrosion depth, however, they showed a much smaller pitting corrosion depth than the untreated ones. It is supposed that the shot-peened surface is more effective in preventing the pitting corrosion than uniform corrosion. The results of this study are expected to be applied effectively to the absorption chillers using LiBr aqueous solution to estimate and reduce the corrosion.

Numerical Study of Fatigue Crack Propagation in a Residual Stress Field Induced by Shot Peening

Shot peening (SP) is a relatively traditional but highly effective mechanical surface treatment that produces a compressive residual stress field in a shot-peened (SPed) surface, which can effectively delay fatigue crack propagation (FCP) and prolong the service life of engineering materials and structures. A multistep analysis method was developed by combining a numerical simulation of the SP process and the LEFM-based (linear elastic fracture mechanics) superposition principle to study FCP behavior in an SP-induced residual stress field. The SP-induced residual stresses were first simulated by a symmetric cell model and then introduced into a finite element model of the CT specimen. The total stress intensity factors and stress ratios with respect to different crack lengths were calculated according to the LEFM-based superposition principle. The influences of external applied load ratios and SP conditions, including one-sided and double-sided SP, on the FCP behavior of the SPed CT specimen were investigated in detail.

Effects of post-processing route on fatigue performance of laser powder bed fusion Inconel 718

Fatigue performance of Inconel 718 (IN718) parts built using laser powder bed fusion (L-PBF) is often poorer than that of the cast and wrought alloy parts. This is because of detrimental effects arising from the microstructures such as brittle phases and anisotropy as well as porosities. To improve fatigue performance of L-PBF IN718, two types of post processes namely hot isostatic pressing (HIP) (performed at 980 °C, 100 MPa and 4 h) and shot peening (performed at 0.45 mmA intensity and 200 % coverage) were employed individually as well as sequentially on different specimens in addition to a standard processing route consisting of L-PBF build followed by solution annealing and double aging heat treatment. Porosities were considerably reduced by HIP-ing (from 0.39 % to 0.08 % porosity volume ratio) but this did not translate to improvements in fatigue performance. This can be attributed to the presence of inclusions and yield strength reduction resulting from γ” solutionisation. High compressive residual stresses of close to 1 GPa were recorded following shot peening regardless of whether HIP-ing was carried out prior to the shot peening. Improvement in fatigue lives particularly at high stress levels was observed on shot peened specimens without HIP-ing (H + SP) which can be explained by the compressive residual stresses that delay the onset of fatigue crack initiation. Shot peening applied on the HIP-ed specimens (H + HIP + SP) however, resulted in fatigue performance deterioration. This is related to the harmful tensile stresses that must exist alongside the compressive residual stresses in a shot peened surface, as evident from the location of the sub-surface crack initiations near the residual stress transition region approximately 300 μm from the free surface. In this case, detrimental effects arising from tensile stresses appear to have outweighed the benefits from compressive stresses on fatigue performance.

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.

An improvement in fatigue behavior of AISI 4340 steel by shot peening and ultrasonic nanocrystal surface modification

Individual and synergy effects of shot peening (SP) and ultrasonic nanocrystal surface modification (UNSM) on rotary bending fatigue (RBF) behavior of AISI 4340 steel were systematically investigated at various bending stress levels in the range of 275–600 MPa. The results revealed that the fatigue behavior of the as-received sample was enhanced by SP and it was further enhanced by SP and UNSM combination, while the UNSM-treated one exhibited the highest enhancement in fatigue behavior. The fatigue behavior of the SP + UNSM sample was enhanced after SP, but it was found to be detrimental after UNSM. Apart from RBF experiments, individual and synergy effects of SP and UNSM on surface roughness, hardness, residual stresses and grain size were analyzed as well. Fractography of the samples was characterized by scanning electron microscope (SEM) and fatigue mechanisms of each sample were discussed based on the obtained observations. The finest grain size and highest compressive residual stress (CRS) obtained by UNSM in comparison with those of the SP and SP + UNSM was responsible for the best fatigue performance.

Enhancement in microstructural and mechanical performance of AA7075 aluminum alloy via severe shot peening and ultrasonic nanocrystal surface modification

In this experimental study, AA7075 aluminum alloy was subjected to pure severe shot peening (SSP), pure ultrasonic nanocrystalline surface modification (UNSM) and the combination of these two treatments. The treated specimens were analyzed with detailed microstructure analysis, micro-hardness, surface roughness, XRD investigations and wear-friction tests. The results demonstrated that UNSM exhibited fine surface finish and provided minimum surface roughness with the Ra value of 0.8 µm. Moreover, UNSM played an important role in the reduction of Ra as a secondary treatment. Electron back scatter diffraction (EBSD) analysis, full width at half maximum (FWHM) evaluations and compressive residual stress (CRS) measurements showed that the deformed layer structure was converted into a nanocrystallized and compressively stressed zone via SSP and UNSM. The hardness on the topmost layer was effectively enhanced by UNSM + SSP and SSP + UNSM processes. The wear and friction performance were particularly improved by two-stage operations of UNSM + SSP and SSP + UNSM. The performance was also compatible with the hardness, residual stress and nanocrystallization investigations.

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.