Shot Peened Layer Research Articles

Surface Residual Stress Release Behavior of Shot-Peened Springs

Shot peening is the primary method used to improve the fatigue life of springs. In this study, we aimed to quantify the reduction in residual stresses in the shot-peened layer by considering factors such as surface roughness, cyclic loading, and the helix angle, based on the spring’s periodic variation and curvature characteristics. We developed an equivalent replacement algorithm to address the challenge of characterizing the dynamic accumulation and attenuation of residual stresses under cyclic multiaxial stresses. This algorithm accurately modeled the dynamic attenuation of residual stresses and was incorporated into the spring life prediction model. Experimental validation demonstrated the high accuracy of the model for predicting fatigue life.

Effect of Various Processes on Microstructure of CoCrFeNiAlx High-Entropy Alloy Shot Peening Layer

The change in microstructure caused by shot peening can strengthen the material and play an important role in improving the fatigue properties of the material. In order to investigate the related properties such as plastic strain anddislocation activity, the microstructure of CoCrFeNiAlx alloy shot peening layer under different processes was studied. The material exhibited a single austenitic phase, and the FCC crystal structure remained unchanged despite variations in shot peening intensity. Microstructure analysis indicates that with the increase in shot peening intensity, the grain size of the shot peening layer decreases obviously, and the content of microscopic distortion on the surface of the shot peening layer is the highest, and gradually decreases with the increase in depth. At the same time, the roughness of the sample surface is also reduced, which can enhance the fatigue strength and life of the sample. A TEM study revealed the microstructure of the shot peening layer. During the impact of shot peening, the twins produced gradually subdivided the initial grain into smaller slices. With the accumulation of plastic strain, dislocation activity begins to dominate the deformation process. The deformation-induced dislocations accumulate gradually in the small pieces and accumulate into dislocations perpendicular to the secondary twins. These results could be conducive to providing reference and theoretical basis for improving and strengthening the mechanical properties of a series of materials such as high-entropy alloy.

Effect of Shot Peening on Oxidation and Precipitation in Inconel 718

In this study, the effect of the surface state on the behaviour of Inconel 718 alloy exposed to 640 ^{circ }C and 700 ^{circ }C environments for times varying between one and one hundred hours was investigated. In particular, the focus was set on the evolution of oxidation and precipitation phenomena during thermal exposure. Three surface states were considered: two generated through shot peening treatments featuring different coverage levels, while the third condition is a non-peened one. Shot peening treatments modify the surface condition and introduce higher residual stresses and microhardness values than in the non-treated condition. The morphology of the oxides appears to be different depending on the condition observed. Regarding the kinetics, over time the oxidation process follows a parabolic trend and appears to be influenced by the surface state; in particular, severe shot peening treatment is characterized by the highest intensity of the phenomenon. However, the order of magnitude of the weight gains measured suggests that the observed variations can be neglected, and that the positive effect of shot peening can be exploited without introducing oxidation problems. From the point of view of the microstructural evolution, an increase in the coarsening kinetics of gamma” phase was observed in the shot peened layer.

Characterization of Distribution of Microstructure and Micro-mechanical Properties of Nickel-Based Single Crystal Superalloy Within the Shot-Peened Layer

Characterization of Distribution of Microstructure and Micro-mechanical Properties of Nickel-Based Single Crystal Superalloy Within the Shot-Peened Layer

Characterization of distribution of residual stress in shot-peened layer of nickel-based single crystal superalloy DD6 by nanoindentation technique

Hardness, elastic modulus, yield strength, work hardening exponent, and residual stress within shot-peened layer of nickel-based single crystal superalloy DD6 were experimentally obtained by nanoindentation under a maximum load of 100 mN. The residual stresses calculated by different models have similar variation with the depth, but the values differ significantly with Wang's model most suitable for shot-peened DD6. It is found: the maximum residual compressive stress is 1.23 GPa at the depth of 40 μm; and the total depth of residual compressive stress layer is 140 μm. Mechanical properties such as indentation hardness and yield strength are affected by residual stress, which has little effect on elastic modulus. The effects of residual stress on various indentation parameters such as indentation work/displacement and contact depth/stiffness were quantified by linear expressions. The microstructural change in the shot-peened layer was found to be associated with the distribution of residual stress.

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.

Elasto-Plastic Fracture Mechanics Analysis of the Effect of Shot Peening on 300M Steel.

A modified J-integral calculation method is adopted to fix the problem of the quantitative evaluation of the crack propagation of shot-peened structures. Considering the residual stress, residual strain, and residual strain energy, the effect of shot peening on the J-integral parameters of semi-elliptic surface crack fronts is quantitatively calculated and a method is provided for the performance evaluation of the shot peening layer. First, the shot peening process is simulated, then the fatigue crack is generated by changing the constraint condition and a far-field load is applied to calculate the J-integral parameters, crack propagation rate, and crack kinking angle. The effects of different crack depths and shot velocities on the fracture parameters are analyzed. The results show that the reduction in the J-integral value after shot peening decreases with the increase in the crack depth when the shot velocity is a certain value, which indicates that shot peening is more beneficial for suppressing the fatigue crack propagation. When the crack depth is greater than the depth of the compressive stress layer, shot peening accelerates the crack propagation. The reduction in the J-integral value decreases with the increase in shot velocity when the crack depth is a certain value; therefore, increasing shot velocity is more beneficial for retarding fatigue crack propagation.

Determination of surface mechanical property and residual stress stability for shot-peened SAF2507 duplex stainless steel by in situ X-ray diffraction stress analysis

In this study, SAF2507 duplex (austenite–ferrite) stainless steel was processed by shot peening. The depth–profile variations of the stress state and work hardening in the shot-peened layer were investigated by X-ray diffraction and microhardness tests. The evolutions of surface morphology and microstructure were investigated using scanning and transmission electron microscopy. The stress–strain relations of the shot-peened surface and surface residual stress relaxation caused by cyclic stresses were experimentally determined by in situ X-ray diffraction stress analysis combined with tensile tests. Results showed that shot peening (SP) has induced severe plastic deformation in the surface layer, with the attendant work hardening and high compressive residual stresses (CRS). Nevertheless, there were incompatibilities in plastic deformation between the phases, and more property improvements represented by higher CRS, peak breadth and microhardness were conferred into austenitic phases. SP notably enhanced the surface yield strength of this two-phase alloy. The surface yield strength σ0.2 of ferrite and austenite were around 780 and 1100MPa after SP, which were 59% and 104% respectively higher than that of the untreated surface. The surface stress relaxation under cyclic tensile loadings consisted of a two-stage process. The surface residual stresses relaxed dramatically within the first cycle (N=1), then decreased linearly with the logarithm of loading cycles (N>1). The more severely deformed microstructures in austenite resulted in higher surface yield strength and contributed to higher cyclic stability of residual stress.

Thermal relaxation of residual stress in shot-peened CNT/Al–Mg–Si alloy composites

A carbon nanotubes (CNTs)-reinforced Al–Mg–Si alloy composite was made and shot peened. After shot peening, a compressive residual stress field was generated in shot peened layer. The change law of residual stress and microhardness with annealing time at elevated temperatures (150°C, 200°C, and 250°C) was investigated. An Al–Mg–Si alloy without CNT addition is prepared in the same process to compare with the CNTs/Al–Mg–Si alloy composite to verify the effect of CNTs on residual stress relaxation. Results showed that for the both materials, macro and micro residual stresses in the shot-peened layers decreased firstly due to thermal recovery and then trend to be stable during annealing process. Increasing the annealing temperature could accelerate the speed of stress release and increase the decrement rate. Specially, the addition of CNTs could improve the thermal stability of the macro residual stress created by shot peening.

Surface mechanical properties of shot-peened CNT/Al–Mg–Si alloy composites

A carbon nanotube (CNT)-reinforced Al matrix composite was fabricated and treated by shot peening. After shot peening, isotropic compressive residual stress fields were induced in surface shot-peened layers. As the mechanical properties of the peened layers were improved and therefore varied from the base metal, a specific in-situ X-ray stress analyzer combined with the tensile test technique was used to measure the stress–strain relationship of the strengthened surface layer. On the basis of the measurement and the Von Mises stress criterion, the surface yield strength was calculated and improved by 25% relative to that of the matrix. Moreover, a relaxation behavior of compressive residual stress was observed under cyclic loading. The results showed that the rapid relaxation of surface residual stress chiefly occurred in the first few cycles and then stabilized gradually in subsequent cycles. The retained residual stress under all given applied cyclic loadings possibly occurred in the compressive state consistently.

Effect of shot-peening treatment on the bio-tribological properties of a Ni+ implantation layer formed on the surface of Ti6Al4V

To improve the bio-tribological properties of the Ti6Al4V surface, the Ti6Al4V alloy was subjected to a shot-peening treatment and a subsequent Ni+ implantation process. The phase composition, phase content and grain size of the resulting Ni+ implantation layer formed on the surface were evaluated via x-ray diffraction. The nano-hardness of the modified layer was measured with a nano-micro mechanical probe. Moreover, after bio-tribological testing, the scratch morphology of the layer was observed with a scanning electron microscope. The results revealed that this layer was composed mainly of Ti2Ni. The shot-peening pretreatment yielded a significant increase in the Ti2Ni content and the nano-hardness of the layer, resulting in grain size refinement of the formation phase. When a Ni+ implantation energy of 45 keV was employed, the Ti2Ni phase content and the grain size of the shot-peened layer increased by 33.6% and decreased by 65.9%, respectively. The corresponding friction coefficients under artificial saliva and a sodium hyaluronate pure water solution decreased by 20.9% and 29.3%, respectively. In the case of samples implanted at an energy of 40 keV, the nano-hardness of the shot-peened layer was 50.8% higher than that of the non-peened layer. Therefore, a shot-peening pretreatment can yield a significant improvement in the properties of the single Ni+ implantation layer on the Ti6Al4V surface.

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

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

Preparation of an Anodized Shot-Peened Layer on Steel and Its Controllable Wettability

In this work, we have presented a detailed study on the effect of shot peening on anodization of medium carbon steel. Anodization has been conducted on both non-shot-peened and shot-peened steel. The results show that shot peening procedure facilitates the subsequent anodization significantly. The mechanism for promoting anodization by shot peening has been discussed. After anodization, the shot-peened steel forms an amorphous α-Fe2O3 film with a geometric pattern. More importantly, the α-Fe2O3 film and the shot-peened layer constitute an anodized shot-peened layer, which exhibits a multi-scale structure. Due to this multi-scale structure, the anodized shot-peened layer shows a controllable wettability. It can be used as a hydrophilic or a hydrophobic coating.

The dual role of shot peening in hydrogen-assisted cracking of PSB1080 high strength steel

The influence of shot peening (SP) treatment on reversible and irreversible hydrogen embrittlement of PSB1080 steel was investigated using slow strain rate tensile tests and electrochemical hydrogen charging-induced cracking tests, respectively. The results demonstrate that SP plays the dual role in hydrogen-assisted cracking. On the one hand, the resistance to hydrogen embrittlement increases as the SP pressure increases for reversible hydrogen embrittlement. This is ascribed to the fact that the shot peening layer acts as a barrier from hydrogen invasion, which is illustrated by hydrogen permeation tests and fracture surface observation. On the other hand, the susceptibility to hydrogen-induced cracking increases with an increase in SP pressure for irreversible hydrogen embrittlement. The crack initiation is associated with inclusions rich in O, Fe, Al and Si or in O, Fe, Si and S for no shot peening sample, while for SP specimen both inclusions and crater rim serve as crack origins. In addition, the hydrogen-induced crack path exhibits a long strip shape for no shot peening sample, whereas the branch-type cracks are observed in SP specimens.

Assessing Shot-Peening Residual Stresses by Using the Incremental Hole-Drilling Technique and Laser Interferometry (DSPI)

The incremental hole-drilling technique was applied to determine residual stress profiles in shot-peened steel layers. The accuracy of using an enhanced Digital Speckle Pattern Interferometry technique for measuring the strain relaxation arising around the drilled holes and, consequently, the in-depth residual stress distribution induced by shot-peening, was evaluated. The experimental results were systematically compared with those determined using standard electric strain-gauges. The X-ray diffraction technique was chosen as reference due to its high accuracy to determine shot-peening residual stresses.

Residual Stress Relaxation of Shot-Peened Deformation Surface Layer on Duplex Stainless Steel Under Applied Loading

The relaxation of residual stress in shot-peened surface layer of duplex stainless steel S32205 under static and cyclic loading was investigated. The results reveal that the compressive residual stress is relaxed under applied tensile stress. The relaxation of residual stress in longitudinal direction is more obvious than that in transverse direction in both austenite and ferrite. When the applied stress is beyond the yield strength of the materials, the relaxation of the residual stress becomes drastic. Under cyclic loading, the residual stress relaxation occurs fast in the first few cycles, it then becomes stable gradually. A model was used to quantitatively calculate the residual stress under cyclic loading with different applied tensile stresses. The relaxation behavior is determined by the applied loading, the number of cycles, dislocation density, and the residual stress gradient. The relaxation behavior difference under cyclic loading between ferrite and austenite is discussed.

Microstructure thermostability of shot peened duplex stainless steel surface layer

Shot peening treatment was employed to introduce deformation into the surface layer of duplex stainless steel S32205, and the microstructure thermostability during isothermal annealing was investigated using X-ray diffraction line profile analysis. Microstructure variation in shot peened layer is observed with the extension of annealing time. The domain growth activation energy and microstrain relaxation energy in both ferrite and austenite were calculated by computer regression analysis. Compared to ferrite, the shot peened austenite exhibits a higher dislocation density, a larger driving force for recrystallisation and relaxation; however, it has higher activation energy of domain growth and higher microstrain relaxation energy. The results show that the microstructure thermostability of austenite is higher than that of ferrite.

Study of anti-laser irradiation performance of shot-peened 40CrNiMoA alloy steel

In this paper, shot-peening treatment was introduced to reinforce an alloy surface to protect it from laser irradiation, and experiments were carried out on 40CrNiMoA alloy steel. Macro-mechanical properties were studied and compared before and after both shot-peening and laser irradiation by conducting tensile and hardness measurements. Experimental results showed that the shot-peened alloy showed better mechanical properties after laser irradiation when compared to the alloy without shot-peening treatment. The enhanced ability of the shot-peened alloy for anti-laser irradiation was explained as due to the large residual compressive stress distributions over the shot-peening layer greatly reducing the thermal shock effect introduced by the laser. On the other hand, the growth of microstructures in specific shape absorbed the thermal energy during irradiation, giving a higher probability for the alloy to resist damage.

The recrystallization behavior of surface deformation layer of (TiB+TiC)/Ti–6Al–4V composite during isothermal annealing

The recrystallization behavior of surface deformation layer of (TiB + TiC)/Ti–6Al–4V and Ti–6Al–4V were both investigated during isothermal annealing using X-ray diffraction line profile analysis. The surface deformation layer was introduced by shot peening treatment. The results revealed that with increasing the time of isothermal annealing, the microstructure variations at shot peened layer were obvious. Based on the results of line profile analysis, the recrystallization activation energies were calculated by computer regression analysis, and it showed that the recrystallization activation energy of (TiB + TiC)/Ti–6Al–4V was larger than that of Ti–6Al–4V, which was ascribed to the effect of reinforcements hindering the movements of dislocations, grain and subgrain boundaries in the process of recrystallization. The hindrance effect of reinforcements as sink sources of dislocations gliding resulted that the decrease rate of dislocation density of the composite was slower than that of the matrix. In addition, the relaxation activation energies were obtained according to the analysis of microstrain relaxation, and after isothermal annealing, the depth distribution of domain sizes from the top surface was investigated and discussed in detail. According to above analysis, the results showed that the thermostability of the composite was higher than that of the matrix because of the effect of reinforcements.

Thermal Relaxation of Residual Stresses in Shot Peened Surface Layer of SiCw/Al Composite

The residual stress relaxation of the shot peened layer on the SiCw/Al composite during isothermal annealing was investigated. The results showed that the residual stresses relaxed in the whole deformation layer especially when the annealing temperature was higher than 200 °C. The relaxation process during isothermal annealing could be described precisely using Zener-Wert-Avrami function. Because of high intensity dislocation around reinforcements producing a large amount of stored energy, the residual stress relaxation activation enthalpy of shot peened SiCw/Al was smaller than self-diffusion activation enthalpy of pure aluminum. According to the analysis of full-width at half-maximum (FWHM) of the shot peened composite in different annealing temperatures, it can be concluded the recovery and recrystallization behavior became intensely when anneal temperature was larger than 200 °C. The small relaxation of residual stress in low annealing temperature was mainly due to partly recovery and recrystallization in a very low level.