Severe Shot Peening Research Articles

Effects of conventional, severe, over, and re-shot peening processes on the fatigue behavior of mild carbon steel

The present study investigates experimentally the effects of different shot peening treatments, including conventional, severe, over, and re-shot peening on microstructure, mechanical properties, and fatigue behavior of AISI 1050 mild carbon steel. Different shot peening treatments were performed using various effective parameters by considering the influences of increasing Almen intensity and coverage. Optical microscopy and field emission scanning electron microscopy observations and X-Ray diffraction measurements were carried out to analyze grains refinement in each shot peening treatment. Microhardness and residual stress measurements were taken from shot peened surfaces to the core material to investigate the mechanical properties. The fatigue behaviors of the specimens were examined by using the axial fatigue test. The results indicated that post-grinding, re-shot peening, and severe shot peening processes have significant effects on fatigue life improvement.

Modelling of Conventional and Severe Shot Peening Influence on Properties of High Carbon Steel via Artificial Neural Network

Shot peening (SP), as one of the severe plastic deformation (SPD) methods is employed for surface modification of the engineering components by improving the metallurgical and mechanical properties. Furthermore artificial neural network (ANN) has been widely used in different science and engineering problems for predicting and optimizing in the last decade. In the present study, effects of conventional shot peening (CSP) and severe shot peening (SSP) on properties of AISI 1060 high carbon steel were modelled and compared via ANN. In order to networks training, the back propagation (BP) error algorithm is developed and data of experimental test results are employed. Experimental data illustrates that SSP has superior influence than CSP to improve the properties. Different networks with different structures are trained with try and error process and the one which had the best performance is selected for modeling. Testing of the ANN is carried out using experimental data which they were not used during networks training. Distance from the surface (depth), SP intensity and coverage are regarded as inputs and microhardness, residual stress and grain size are gathered as outputs of the networks. Comparison of predicted and experimental values indicates that the networks are tuned finely and adjusted carefully; therefore, they have good agreement.

Effect of severe shot peening and ultra-low temperature plasma nitriding on Ti-6Al-4V alloy

In this study, the fatigue behavior of Ti-6Al-4V alloy is tend to be improved by severe plastic deformation via shot peening and plasma nitriding. Shot peening with sub-branches: Conventional shot peening (A12-14), severe shot peening (A28–30 and A34-36) and repeening (N6-8) are exposed. Besides plasma nitriding is implemented at 500 °C, 550 °C and 600 °C with the durations of 4, 8 and 16 h. Due to utilization of shot peening as prior severe plastic deformation during diffusion of nitrogen, two methods are applied in sequence. Severe shot peening forms ultra-fine crystals and oriented grains by disintegrating of α and β phases just below the surface and increases surface roughness. Plasma nitriding temperature increase the compound layer thickness and the treatment leads to vanish of β particles through a certain line for diffusion layer. Prior severe plastic deformation by severe shot peening generally triggers the formation of thicker compound layer and emerges distinct diffusion depth with finer and oriented precipitation. The phase's intensity obtained from XRD peaks has been amplified by the application of prior shot peening. Each shot peening provides fatigue improvement on the other hand plasma nitriding application regardless of being pre or post treatments diminish the fatigue resistance.

Effects of nanofeatures induced by severe shot peening (SSP) on mechanical, corrosion and cytocompatibility properties of magnesium alloy AZ31.

A major challenge for most commonly used metals for bio-implants is their non-biodegradability that necessitates revision surgery for implant retrieval when used as fixation plates, screws, etc. Magnesium is reported among the most biocompatible metals that resorb over time without adverse tissue reactions and is indispensable for many biochemical processes in human body. However, fast and uncontrolled degradation of magnesium alloys in the physiological environment in addition to their inadequate mechanical properties especially under repeated loading have limited their application in the biomedical field. The present study providesdata on the effect of a relatively simple surface nanocrystallziation method with high potential to tailor the mechanical and chemical behavior of magnesium based material while maintaining its cytocompatibility.

Correlation between the surface coverage of severe shot peening and surface microstructural evolutions in AISI 321: A TEM, FE-SEM and GI-XRD study

Severe shot peening (SSP) as a surface severe plastic deformation (S2PD) process over a wide range of coverages was applied to generate gradient microstructures with the grain size increasing from nanometer- and micron-scale to initial grain size on the surface layers of 321 stainless steel. The microstructural evolutions including the grain size distribution and phase transformation were systematically investigated in-depth for different surface coverages. GI-XRD, FE-SEM and TEM techniques were used to reveal the microstructure modification mechanisms as a function of the surface coverage. Experimental results show that dislocation slip plays a key role in the grain refinement of this alloy so that with increasing the surface coverage, different structures including dislocation walls, dislocation tangles, and lamella-shaped cells sequentially appear in the initial coarse grains. The results confirmed that these dense dislocation structures during ultrahigh plastic deformation produce ultrafine- (115–192nm) and nano-grains (68–82nm) to minimize the total energy of the system. In line with the grain refinement, the γ (austenite)→α′ (straininduced martensite) phase transformation is more affected as the plastic strain increases. So that the volume fraction of α′ phase increases to 58.4% for ultrahigh strains. Gradient variation of microhardness with the depth was also obtained for various samples.

Thermal stability of nanocrystalline surface layer of AISI 321 stainless steel

A nanocrystalline layer with an average grain size of 75 nm was formed on the top surface layer of 321 stainless steel (321SS) alloy via severe shot peening (SSP). Grazing incidence X-ray diffraction (GI-XRD) and transmission electron microscopy (TEM) were applied to characterize the grain size changes, phase compositions and microstructure evolution after vacuum annealing at temperatures ranging from 200 °C to 1000 °C. The results revealed that nanograins slowly grow to ≈411 nm as the temperature increases to 600 °C. Dislocation annihilation is shown to be responsible for the changes in grain size up to 600 °C. However, an abnormal grain growth is observed at annealing temperatures of 800 °C and 1000 °C in which grains grow to ≈1267 nm and ≈2012 nm, respectively. This abnormal grain growth is attributed to the synergistic effect of dislocation annihilation in grain boundaries and triple points, re-arrangement of dislocations, and formation of middle angle (13°–17°) grain boundaries. Transformation of stress induced martensite (α′) to austenite (γ) and microhardness evolution in the nanocrystalline top surface layer during annealing are also discussed.

Improvement of fatigue endurance of welded S355 J2 structural steel by severe shot peening

ABSTRACTThis work deals with the fatigue resistance of welded joints manufactured from EN S355 J2 structural steel and the possibility of improving fatigue characteristics by the severe shot peening (SSP) surface treatment. Fatigue testing was carried out by the rotating bending test on specimens manufactured from the base material (BM), welded material and welded material treated by SSP. Results have shown big scatter in obtained results from as-welded material and overall reduction of fatigue endurance when compared to the BM. SSP applied on the welded joints has reduced the scatter of experimental data and increased the fatigue strength. Obtained results of fatigue tests are compared, discussed and supported by correlation with results of additional experiments, e.g. metallographic analyses, microhardness tests, residual stresses measurements and surface roughness measurement.

Effect of Shot Peening Coverage on Surface Nanostructuring of 316L Stainless Steel and its Influence on Low Temperature Plasma-Nitriding

Abstract Air-blast shot peening (ABSP) is a cost effective and industrially viable technique to produce nanostructured surface layer on metallic materials. In the present study, 316L stainless steel samples were subjected to shot peening at different peening coverage, from conventional to severe peening. Nanocrystalline structure was observed on the sample surface after peening and mechanical twins; intersection of multidirectional twins producing rhombic blocks were observed in the subsurface layer. Peening process led to the formation of strain induced martensite (α‘), and its fraction was found to increase with the coverage. Depth of nanostructured layer and surface microhardness also increased with the increase in coverage, whereas surface roughness followed an opposite trend. Both peened and un-peened samples were subjected to plasma nitriding at 400°C for 4 h. Uniform and appreciably high case depth of about 45 μm was observed in severely pre-peened (1000 % coverage) sample after nitriding treatment. No precipitation of CrN was observed. This highlights the marked influence of severe shot peening as a pre-treatment for low temperature plasma nitriding of austenitic stainless steels.

Surface nanocrystallization and gradient microstructural evolutions in the surface layers of 321 stainless steel alloy treated via severe shot peening

The gradient nanocrystalline structure from the top surface to the subsurface layers of 321 austenitic stainless steel alloy was fabricated by means of severe shot peening. The microstructural evolutions including the grain size distribution and phase transformation were investigated in-depth. Experimental results showed that the dislocation slipping plays a key role in the grain refinement of this alloy and depend on the amount of imparted plastic strain, different structures including dislocation walls, dislocation tangles, mechanical twinning, lamella-shaped cells are sequentially appeared in the surface and/or subsurface grains. Due to imparting ultrahigh plastic deformation in the topmost surface, mentioned structures are converted to the nano-grains (68–82 nm) to minimize the total energy of the surface layer. In line with the grain refinement, austenite to strain induced martensite phase transformation is more affected as the plastic strain increases so that the volume fraction of latter phase reaches to 65% in the topmost surface. As a result of these evolutions, microhardness values are decreased from 281 to 120 HV in the surface layers.

An investigation of the properties of conventional and severe shot peened low alloy steel**This work was presented in the shot peening section during ‘The 30th International Conference on Surface Modification Technologies, 2016, Milan, Italy’ (SMT30, ID 61, entitled ‘Comparison of the effects of conventional shot peening and severe shot peening processes on the mechanical and tribological properties of shot peened

The effects of the conventional shot peening and severe shot peening process on the mechanical and tribological properties of shot peened AISI 4340 high strength steel were systematically investigated. Compared with the conventional shot peened sample, the ultrafine grain surface layer with a depth of about 20 µm generated by the severe shot peening process can enhance the hardness and wear resistance of the treated material. However, deeper dimples generated by the high media velocity in the severe shot peening process resulted in a higher surface roughness, which is considered as a side effect of this method reducing the fatigue life of the material. Applying a smaller shot size with an appropriate intensity can be used to peen the severe shot peened samples to not only reduce the surface roughness and friction coefficient but also improve the wear resistance for these samples.

Influence of Severe Shot Peening on the Surface State and Ultra-High-Cycle Fatigue Behavior of an AW 7075 Aluminum Alloy

The ever more pressing and concurrent requirements of light design, increased performances and reliability, energy savings together with acceptable costs, is always pushing researchers and engineers toward the definition and application of new materials and treatments, able to guarantee superior properties and adequate repeatability and reliability. This means that one step beyond the definition of a potentially successful solution, a complete characterization of the new materials is needed, in order to get the right data and use them in the design process. A promising severe plastic deformation surface treatment to improve the fatigue properties of materials and metal parts is considered in this paper. The used treatment is called the severe shot peening, and it is derived from the conventional shot peening but with use of unusually high peening parameters. It was proven that it is able to generate a nanostructured surface layer of material, which results in superior fatigue properties when applied to many structural materials. The severe shot peening is applied to an AW 7075 Al alloy, widely used in mechanical and aeronautic constructions and the effects of such a treatment on this material are investigated in this paper, with particular emphasis on the ultra-high-cycle fatigue behavior. The results address the choice of the correct treatment parameters for getting an evaluable advantage of this treatment and are critically discussed for a complete understanding of the mechanisms leading to the modified fatigue behavior, in view of the future developments and research in the field.

Influence of different shot peening treatments on surface state and fatigue behaviour of Al 6063 alloy

Shot peening is a surface treatment commonly used to improve the fatigue behaviour of mechanical components. It consists in bombarding metallic surfaces with spherical shots to induce plastic deformation in the surface layer of the material. Recent studies have shown that, if applied with unconventional parameters, namely severe shot peening, it can be considered a severe plastic deformation surface treatment, able to strongly modify the microstructure of the surface layer of material by generating grains in the scale of nanometers. In this paper, different shot peening treatments with conventional and severe parameters were performed on aluminium 6063 alloy in order to assess the differences induced in the microstructure of the surface layer, and to evaluate their effects on fatigue behaviour. Rotating bending fatigue tests were performed on shot peened hourglass specimens. Specimens’ microstructure, surface roughness, microhardness and residual stress profiles were carefully characterized. The obtained results evidence the notable influence of shot peening parameters on surface layer microstructure, which at the same time influences fatigue behaviour.

Severe Shot Peening to Get a Nano-Structured Surface Layer in Low-Alloy Steel

Shot peening is a cold work treatment that consists in impacting a metallic surface with a flux of spherical shots with the aim to introduce compressive residual stresses field and work hardening on the surface layer. Both aforementioned parameters are responsible for improved fatigue behaviour of treated components. Recent studies have shown that if applied using severe parameters (severe shot peening), this treatment can be categorized as a severe plastic deformation surface treatment. Severe shot peening is able to strongly modify the microstructure of the surface layer of material by increasing the dislocation density that define new grain boundaries and progressively form ultrafine structure. In this work, conventional shot peening and severe shot peening treatments were applied to 39NiCrMo3 steel samples with the aim to study the microstructural changes. The samples were also characterized in terms of surface roughness, micro hardness, residual stresses, and surface work-hardening. Particular attention was focused on the microstructural analysis as a function of the coverage level, with the aim to assess the evolution of grain size from the surface to the inner material and induced gradient microstructure. The results indicated that severe shot peening causes a more remarkable improvement of the general surface mechanical characteristics with respect to conventional shot peening, and revealed a notable microstructural alteration induced by the treatment.

On the effectiveness of surface severe plastic deformation by shot peening at cryogenic temperature

The effect of cryogenic temperature (CT) on the graded microstructures obtained by severe shot peening using surface mechanical attrition treatment (SMAT) was investigated for two austenitic steels that used different mechanisms for assisting plastic deformation. For the metastable 304L steel, the depth of the hardened region increases because CT promotes the formation of strain induced martensite. Comparatively, for the 310S steel that remained austenitic, the size of the subsurface affected region decreases because of the improved strength of the material at CT but the fine twinned nanostructures results in significant top surface hardening.

Microstructural characterization of low temperature plasma-nitrided 316L stainless steel surface with prior severe shot peening

Surface nanocrystallization by severe deformation has proven beneficial as pre-treatment to plasma nitriding. It aids in achieving thicker nitride layers at lower temperatures thus making the process more economical. In austenitic stainless steels, severe deformation leads to formation of strain induced martensite on the surface while plasma nitriding alone forms expanded austenite. However, structural characteristics of surface layer of pre-deformed steel after plasma nitriding is still a matter of debate. In present study, 316L stainless steel was subjected to severe shot peening: followed by plasma nitriding at 400°C for 4h. Characteristics of sample surface before and after treatment were analyzed by scanning electron microscopy, X-ray diffractometry and transmission electron microscopy techniques. Results showed that, this duplex treatment leads to formation of about 45μm thick nitride layer; without CrN precipitation. This is significantly high compared to reported data considering the temperature and duration of nitriding treatment employed. Selected area electron diffraction pattern from topmost surface confirmed the co-existence of austenite and martensite while subsurface layer was predominantly consisting of lath martensite. This indicates that major phase in the nitrided layer is martensitic in nature and nitrogen supersaturation leads to transformation of small fraction of martensite to expanded austenite.

Novel Type Shot Peening Applications on Railway Axle Steel

In this study, novel type shot peening applications such as severe shot peening (SSP) and dual step peening -DSP- (severe shot peening followed by re-peening -RP-) have been applied to AISI 4340 railway axle steel. Microstructural and mechanical properties are compared with conventionally shot peened (CSP) ones. The new treatments influence thicker surface layer and improve mechanical properties (microhardness and fatigue) by the way of Almen intensity enhancement. Disadvantageously, SSP increase surface roughness to the values that can be hazardous to the expected fatigue life of critical machine parts. However, DSP reduces the values and new approaches could be designed for making surface roughness values comparable with CSP in the aspect of the experimental outputs.

Synergetic effect of thicker nanocrystalline structure with high amount of strain induced martensite on surface characteristics of plasma nitrided austenitic stainless steel

Abstract Severe shot peening is a simple and effective method to synthesize nanocrystalline layer on metallic surfaces. A new reactor to synthesize thicker nanocrystalline layers on metallic surfaces by shot peening is presented. In this cylindrical reactor air enters inside the reactor tangentially, propels shots on the specimen to be shot peened and leaves the reactor after multiple rotations. Air vortex and very high turbulence formed inside the reactor dissipate heat generated during shot peening and thus suppress dynamic recovery which promotes formation of refined and thicker nanocrystalline structure on a metallic surface. Experiments were conducted on 5specimens of austenitic stainless steel with different shot velocities in the reactor. Characterization (X-ray diffraction profiles, cross-sectional optical micrographs, TEM and micro-hardness profiles) of shot peened surfaces showed that thicker nanocrystalline/nano-twinned layers were developed during all peening conditions used in the experiments. Microstrain in the lattice, dislocation density and volume fraction of strain induced martensite observed to increase with rise in shot velocity. Specimens with thicker nanocrystalline layers were prepared. These specimens contained high amount of strain induced martensite deep down the surface. Plasma nitriding of these pre-shot peened specimens were done at 425 °C and 500 °C for six hours. Presence of thicker nanocrystalline layer with high amount of martensite at the surface of austenitic stainless steel observed to have synergetic effect and significantly influenced kinetics of nitriding process leading to higher surface hardness and 6-fold thicker nitrided layers compare to untreated nitrided surface. Presence of nanocrystalline structure, however, also effects on precipitation of chromium nitrides during nitriding.

Nanoscale surface modification of AISI 316L stainless steel by severe shot peening

Surface nanocrystallization is gaining increased attention due to its high potential of enhancing mechanical functionality and modulating material's interaction with the surrounding environment. Among mechanical approaches, severe shot peening has recently shown to be a very promising technique for surface grain refinement, considering its efficiency, eco-friendliness, relative low cost and minimum geometrical restrictions. This study evaluates the effect of severe shot peening on microstructural and mechanical properties of 316L stainless steel, which is widely used in biomedical, food preparation, structural and marine applications. 316L samples, shot peened with different peening parameters, were studied in terms of morphological and structural features, defect density, grain size, phase transformation, surface topography, surface wettability, residual stresses and microhardness. The results indicated that severe shot peening induced near surface grain refinement to nano and sub-micron range and transformed the austenite phase into strain-induced α’- martensite in a layered deformation band structure. Severe shot peening also induced compressive residual stresses and work hardening in the top surface layer. Surface roughness and surface wettability, both of which favorably contribute to modulating the interaction of material with biological environment, were also notably enhanced by severe shot peening.

Influence of different combined severe shot peening and laser surface melting treatments on the fatigue performance of 20CrMnTi steel gear

In this paper, the effect of severe shot peening combined with laser melting (LSMSSP for short) on the fatigue resistance of 20CrMiTi steel gears is investigated in comparison with the effect of traditional shot peening on the fatigue resistance of the laser surface melted (LSMTSP for short) 20CrMiTi steel gear. The surface characteristics of the gear have been analyzed by a scanning electron microscope (SEM) and an X-ray diffractometer (XRD). The Forschungsstelle für Zahnräder und Getriebebau (FZG) back-to-back spur gear test rig was used for fatigue experiments. Experimental results showed that the residual stresses, full width at half maximum (FWHM), microhardness and retained austenite of the LSMSSP gears and LSMTSP gear were entirely different. Although the LSMSSP gears had higher surface roughness than the LSMTSP gear, the LSMSSP gears still had better fatigue resistance than the LSMTSP gear and laser surface melted gear. The nanocrystallized surface layer on the gear tooth flank created by severe shot peening might be a very important factor for improving the fatigue property of the LSMSSP gears.

Modeling of Severe Shot Peening Effects to Obtain Nanocrystalline Surface on Cast Iron Using Artificial Neural Network

Severe plastic deformation methods such as severe shot peening are used in order to improve mechanical properties of the components by surface microstructure nanocrystallization. Severe shot peening is one of the popular mechanical surface treatments generally aimed at generating nanograined layer and compressive residual stress close to the surface. Moreover, artificial neural network has been used as an efficient approach to predict and optimize the engineering problems. In present study effects of conventional and severe shot peening on cast iron were modelled by means of artificial neural networks and they were compared. The obtained results indicate that severe shot peening has superior effects on improvement of materials mechanical and metallurgical properties than conventional shot peening. Back propagation error algorithm and data of experimental tests on nodular cast ironwith ferrite-pearlite matrix were employed to train networks. Neural network testing was carried out using different experimental data which they were not used during networks training. In present paper distance from the surface is regarded as an input parameter and microhardness, residual stress and full width at half maximum are gathered as output parameters. The predicted values for full width at half maximum, microhardness and residual stress have the least statistical errors, respectively. The results demonstrate that there is a reasonable and applicable agreement among the experimental and predicted values, illustrating that the developed neural network can be employed to model the conventional and severe shot peening processes.