Compressive Residual Stress Profile Research Articles

Effect of compound surface modification of shot peening and DLC coating on surface integrity and fatigue properties of gear steel 16Cr3NiWMoVNbE

We conducted a study on the surface compound modification of shot peening and pure carbon DLC coating to simultaneously meet the requirements of wear resistance and fatigue resistance of spline structure. The effects of surface compound modification were investigated on the surface morphology, residual stress profile, microstructure, and nano-indentation hardness of 16Cr3NiWMovNbE gear steel, and conducted a comparative study on fatigue performance. The results show that the surface compound modification inherits the surface morphology and compressive residual stress gradient of shot peening, while the surface residual stress is slightly smaller than that of shot peening. In addition, surface compound modification still reflects the characteristics of high hardness and high fracture resistance of DLC coatings. Under the bending load based on spline tooth root, compared to the original specimen, the fatigue life after shot peening, pure carbon DLC coating, and surface compound modification is increased by 3.68, 2.35, and 3.36 respectively. Although the compound modified surface still maintains the shot peening morphology with a increasing surface roughness and stress concentration coefficient, the 100 μm-depth compressive residual stress profile and the subgrain refinement layer introduced, as well as the hard surface layer with good load-bearing capacity, have played the role of fatigue strengthening.

An analytical model for predicting residual stress in shot peening with strain energy method

In this study a model by novel analytical approach is developed and experimentally verified for shot peening residual stress distribution. The residual stress field induced by single shot impact is calculated by using Glinka–Molski energy-based method and kinematic hardening model. The formulation of the compressive residual stress (CRS) distribution is often based on plane strain or plane stress. It can be determined from the derived relation presented in this paper, the final residual stress in the full coverage conditions is the average of the two strain and stress plane expressions proposed by previous researchers. The distribution of residual stress is one of the key differences between the profiles produced by the results of the current model. There is a significant distinction between surface residual stress and maximum CRS, because the CRS profile near the surface is more curved compared to profiles obtained in earlier analytical models. The experimental data obtained by XRD analysis indicate the correctness and precision of the current model. Another goal of this study is to increase the fatigue life of GTD-450 stainless steel by shot peening at two different peening intensities. The fatigue life of samples were obtained by rotary bending test. Analytical results that confirmed by experimental findings shown bigger maximum compressive residual stresses occurred in higher shot peening intensities. This incident can improved fatigue life by deeper plastically deformed layer.

Effect of shot peening with different peening intensity and coverage on surface integrity of Inconel 718 alloy

Shot peening, which usually serves as a final treatment on the components’ surface, greatly alters the surface geometrical and mechanical states. In this study, shot peening experiments using ceramic beads with a diameter of 0.3 mm are performed on the Inconel 718 alloy with varied peening intensity and coverage. The surface roughness, microhardness, and residual stress from shot peening and turning are characterized by a laser scanning confocal microscope, Vickers hardness tester, and X-ray diffraction to evaluate the influence of peening parameters. The results show that the shot peening treatment decreases the surface roughness of the specimens, and the roughness decreases with increasing intensity in the range of 0.13-0.17 mmA. Moreover, the shot peening intensity has a greater influence on the microhardness and residual stress of the shot peening surface compared with coverage. A surface with a large compressive residual stress profile (-1221 MPa in the axial direction) and a high hardness gradient (538.3 HV0.2 at a depth of 50 μm) is formed after the TPI3C3 process (shot peening with the peening intensity of 0.17 mmA and coverage of 300% after turning). The results of this research will provide guidance for developing more effective shot peening strategies.

Turning/Shot peening of Nickel-based powder metallurgy superalloy: Effect on surface integrity and high-temperature low-cycle fatigue properties

In this study, a nickel-based powder metallurgy alloy was processed via turning, ceramic bead peening, and shot peening by high-intensity cast-iron shots and low-intensity ceramic beads (denoted as compound shot peening). We investigated the surface morphology (surface stress concentration factor, Kst), the surface residual stress profile, microstructure, and the hardness gradient of three surface states and compared the high-temperature low-cycle fatigue lives. The results showed that the surface stress concentration coefficients after turning, ceramic bead peening, and compound shot peening were 2.39, 1.98, and 2.12, respectively. The average surface roughness, Sa, after turning was low, but the bottom of the tool mark was sharp, so the Kst value was higher than that after shot peening, which formed a round bottom by bead blasting. Compared with ceramic bead peening, a surface structure with a deeper compressive residual stress profile and a higher hardness gradient was formed after compound shot peening, and nanostructured features appeared on the outermost surface. The estimated low-cycle fatigue lives after the ceramic bead peening and compound shot peening were 0.99 and 3.13 times longer than after the turning process respectively with strain amplitude 0.5% at 538℃. Moreover the gain of compound shot peening on low cycle fatigue performance gradually decreases with the increase of the strain amplitude.

A Multiscale Study on Machining Induced Surface Integrity in Ti-6Al-4V Alloy

This study adopted a multiscale surface integrity approach (macro, micro, and sub-micro scale) to study the effects of cutting conditions and varying cutting fluid applications on the final surface state in Ti-6Al-4V alloy. Surface integrity parameters that were studied in this work are surface roughness, subsurface microhardness, residual stresses, and microstructural alterations. The results show that there is some correlation between microstructural and mechanical characteristics of machining-induced surface integrity. Also, different residual stress profiles were obtained for TMQF (Targeted Minimum Quantity Fluid) machining (compressive residual stress profile) and flood machining (tensile residual stress profile), which underlines the importance of selecting the right cutting fluid application. This work could aid in choosing the right cutting fluid application for the finish machining operation of Ti-6Al-4V alloy to obtain a desired final superior surface integrity. TMQF application conditions produced better surface integrity metrics (lower surface roughness, compressive surface residual stresses, and no undesirable microstructural damage) compared to flood fluid application while finish machining of Ti-6Al-4V titanium alloy.

Optimal shot peening residual stress profile for fatigue

Shot peening (SP) is frequently used as a palliative measure against metal fatigue in many engineering components. The performance of this surface treatment depends on different factors including the material, shape and loading conditions of the component, as well as process parameters. Fatigue improvement due to SP depends to a great extent upon the in-depth compressive residual stress profile produced in the specimen.In this work, we study the optimum shape for a residual stress profile in terms of fatigue behaviour. For this task, we assume a residual stress profile that is qualitatively similar to that produced by SP in many metals. Based on this generic profile, we analyse the optimum shape for two simple, but noteworthy, fatigue cases: plain fatigue and notch fatigue. The analysis is conducted in the “fatigue damage tolerance design” framework, in which a certain initial defect is assumed to be present in the component under study.

A pragmatic approach for assessment of laser-induced compressive residual stress profiles

Laser hardening is a very efficient technique for local surface treatment, however, in case of complex and large components robust processing is highly challenging due to limitations in terms of the absolute size of the overall heat-affected zone. As is shown in the present work, an increased in-depth effect can be achieved by tailoring the laser parameters without melting the surface layer. Optimization of process parameters leads to an elaborate test design demanding numerous verification measurements to determine essential material properties. In this context, the evaluation of compressive residual stress values in the surface layer is very important, e.g. in case of fatigue loaded components. However, residual stress profile measurements obtained by X-ray diffraction are very time-consuming and, thus, can significantly impair the laser parameter development cycle. For this reason, the present study introduces a novel pragmatic approach allowing for qualitative evaluation of laser-induced compressive residual stress states, in particular for multiple laser pass processes based on a Gaussian-like intensity profile. Based on straightforward analytical evaluation, several characteristic features of the affected surface layer, e.g. the position of the residual stress transition zone, can be correlated to a change of the local energy input. A novel parameter referred to as modified area energy is established in present work for this purpose. This novel energy approach provides for an essential contribution to the field of laser hardening to considerably shorten the experimental effort within the laser parameter search.

Effects of surface nanocrystallization on the anodic oxidation behavior of Aluminum

Gradient microstructures on the surface of metals induced by severe shot peening (SSP) is relatively a new research topic in the field of severe plastic deformation processing. The treated surface is known to show three distinct features: a spectrum of grain size from nanometer to sub-micron to micron regime, a work-hardened surface layer, and a compressive residual stress profile near the surface. The current study is defined to investigate the effects of SSP pre-preprocessing on the anodization behavior of Aluminum. Gradient microstructures were obtained on AA1050 Al substrate using SSP with different coverage levels. SSP was performed with ceramic media to prevent contamination of the treated surface. Then the treated surface was anodized at a constant voltage in a sulfuric acid solution. The current-time responses were recorded to study the reaction kinetics. The average grain size on the surface treated by SSP was evaluated to be 255.6 nm and 181.5 nm for 1000% and 2000% coverage levels, respectively, using X-ray diffraction; while the Vickers microhardness was increased from 10.8 HV for the untreated sample to 19.8 HV and 25.8 HV by SSP with 1000% and 2000% coverage levels, respectively. It was found that the nanocrystalline microstructure of Al substrate enhances the growth rate of anodic oxide. A variable growth rate is detected within the treated layer. The nucleation of anodic oxide nanopores is discussed in terms of underlying oxide formation mechanisms and the extent of surface grain refinement.

Investigation on residual stresses in milling of Ti-6Al-4V for both rake and flank application of different MWF strategies

Abstract This study investigates the effects of both rake and flank applications of different Metal Working Fluid (MWF) strategies on residual stresses in the machining of Ti-6Al-4V alloy. Cryogenic (Liquid CO2), Minimum Quantity Lubrication (MQL) and emulsion strategies were studied with modified CoroMill600 milling cutter via internal channels delivering media to insert rake face and flank face. The cutting force, minimum chip thickness and chip morphology were analyzed to understand more about this novel approach of rake and flank delivery of different MWFs in milling. The results reveal the formation of compressive residual stresses until 55-60µm beneath the machined surface irrespective of the type of MWF strategies. The highest value of compressive residual stress was observed at the machined surface of liquid CO2. The magnitude of the traced compressive residual stress profile shows a trend of positive slope gradient beneath the surface for both parallel and perpendicular to feed directional residual stress components. In contrast, residuals stresses in emulsion and MQL strategies were observed with a different trend in generation of compressive residual stress components, where the parallel to feed directional component shows an inflection point with a an initial negative slope gradient followed by a positive one to beneath the machined surface. An increase in the cutting forces and minimum chip thickness values were also observed for liquid CO2, due to the high shear resistance of Ti-6Al-4V alloy at machining zone, which was confirmed from the chip morphology analysis. Overall results show that cryogenic CO2 leads to higher compressive residual stresses at the surface and positive slope gradient beneath the material. The higher cutting forces in Z-axis and minimum chip thickness value in liquid CO2 are also attribute to the higher compressive stresses in Ti-6Al-4V workpiece at cryogenic CO2 environment.

Effect of low-temperature surface hardening by carburization on the fatigue behavior of AISI 316L austenitic stainless steel

The influence of low-temperature gaseous carburization on the fatigue behavior of AISI 316 L austenitic stainless steel was investigated. Tension-compression axial fatigue tests were performed under ambient conditions on untreated and carburized AISI 316 L. The results show that the carburized AISI 316 L has a 22% higher endurance limit compared to untreated AISI 316 L. Fractography investigations with scanning electron microscope (SEM) reveal that for the untreated AISI 316 L fatigue cracks initiate at the surface regardless of the applied stress level. For the carburized AISI 316 L fatigue cracks initiate at the surface for relatively high-level stresses; for relatively low-level stresses fatigue cracks initiate at inclusions beyond the carburized case. After carburization, the ductility in the outmost 10 μm of the carburized case has significantly reduced, leading to micro-crack occurrence during fatigue tests and associated relaxation of compressive residual stress in this region. Beyond this surface-adjacent region, no evident stress relaxation occurs due to the enhanced yield strength of the carburized case. The enhanced fatigue performance is mainly ascribed to the compressive residual compressive stress profile introduced by the carbon-concentration profile over the case. Moreover, solid solution strengthening by interstitially dissolved carbon contributes to improve the fatigue performance.

Effects of process combinations of milling, grinding, and polishing on the surface integrity and fatigue life of GH4169 components

The nickel-based superalloy GH4169 is widely applied in the aviation industry due to its outstanding mechanical properties. However, many blades of GH4169 are still produced by milling and manual polishing, which is costly and unreliable. In this article, GH4169 superalloy components manufactured with combination processes of milling, grinding, and polishing were comparatively studied involving surface integrity and fatigue performance. Test results indicate that the final polishing is the most dominant process that influences the high-cycle fatigue life of GH4169 components. Samples produced via cubic boron nitride grinding and numerical control polishing with a diamond-rubber wheel exhibit fatigue limits of 150 MPa higher than the milled and manually polished samples. Cubic boron nitride grinding induces a considerable compressive residual stress profile with a magnitude of -930 MPa and a depth of 200 μm. Milling induces a typical “hook” residual stress profile with 318 MPa at the surface. Polishing affects the machined surface by two ways, the removal effect and the squeezing effect. The squeezing effect induces a shallow compressive residual stress with approximately −1000 MPa, therefore improves the surface condition. However, inevitable omissions, scratches, texture disorders, and knock marks in hand-polishing are the main causes of the unstable high-cycle fatigue life of hand-polished components.

Enhanced Fatigue Behavior in Quenched and Tempered High-Strength Steel by Means of Double Surface Treatments

The aim of this study is to maximize the fatigue life of a high-strength steel. For this purpose, two different kinds of double surface treatments were studied: shot peening plus vibratory finishing and shot peening plus grit blasting. First, a high-intensity peening treatment was applied, with the aim of inducing a deep region submitted to high compressive residual stresses, and a second surface treatment was followed, to reduce the roughness induced in the first treatment and mitigate the damage produced on the specimen surface. The use of such double treatments was demonstrated to be a good choice to achieve high surface hardening and deep compressive residual stress profiles and to minimize surface defects. The fatigue life of the steel was greatly enhanced following the application of both double surface treatments. A vibratory treatment applied for 24 h after the application of a previous shot peening treatment was able to increase the average fatigue life of the single shot-peened samples almost sevenfold, but a much greater fatigue enhancement was produced using grit blasting for only 60 s. Anyway, both second treatments are able to remove the damaged surface layer produced in the first high-intensity shot peening treatment. The obtained results also revealed that an appropriate combination of surface treatments (shot peening + secondary treatment) avoided the initiation of cracks at the surface of the specimens under cyclic bending loads. Instead, crack initiation took place beneath the compressive residual stress field, induced in alumina inclusions that acted as stress concentrators.

Prediction of residual stress profile and optimization of surface conditions induced by laser shock peening process using artificial neural networks

The purpose of this paper is to predict the compressive residual stress profile induced by the laser shock peening process and to optimize the surface conditions on a Ti-6Al-4V titanium super-alloy using the new technology based on the artificial neural networks. This study covers two principal cases: (i) The numerical analysis: the compressive residual stress distribution induced by the laser peening process is simulated based on the finite element method using ABAQUS software (ABAQUS/Explicit code). (ii) The mathematical modeling analysis: the using of the artificial neural network technique has been proposed to predict the residual stress profile induced by the laser shock processing in order to optimize the laser shock peening surface conditions. To train the artificial neural network, we use different numerical experiments measurements as training and test data. The best fitting training data set was obtained with four neurons in the hidden layers. After training and as seen from the mathematical experiments, the calculated residual stress and the damage state are obviously acceptable. The principal goal of this research paper is to predict the surface treatment state induced by the laser shock peening based on the artificial neural networks technique and on the numerical results without making multiple simulations that can take much more time.

Effects of low intensity shot peening treatments applied with different types of shots on the fatigue performance of a high-strength steel

The aim of this research is to study the fatigue life enhancement produced in a quenched and tempered AISI4340 steel with a tensile strength of 2000 MPa after being submitted to shot peening surface treatments. These treatments generate compressive residual stress fields in a superficial layer of the material at the same time as inducing some kind of damage on the surface. Different kind of projectiles were chosen to perform the treatment (ceramic and steel shots), studying the way these affected the fatigue life of the specimens.The surface topography of the samples was analysed using a roughness tester and by means of scanning electron microscopy (SEM). The compressive residual stress profile induced by these treatments was measured using X-ray diffraction (XRD) plus electro-polishing. The fatigue behaviour of the treated samples was subsequently studied by means of 4-point rotating bending tests and their fracture surfaces were analysed using SEM.The best fatigue performance was obtained after shot peening with ceramic beads under an 8A Almen intensity. The main difference in relation to the treatment performed under the same intensity but using steel cut wire shots was the much lower surface damage induced by the impacts with the ceramic shots compared with the cut wire projectiles, which in turn is justified by the greater geometric perfection and hardness of the former. Furthermore, fatigue specimens shot peened with ceramic beads under an 8A intensity always gave rise to internal fatigue crack initiation, which took place outside the zone subjected to residual compressive stresses. Moreover, fatigue initiation was always linked to the presence of hard and rigid alumina inclusions, which acted as microstructural stress concentrators.

Surface integrity and corrosion performance of biomedical magnesium-calcium alloy processed by hybrid dry cutting-finish burnishing.

Biodegradable magnesium-calcium (MgCa) alloy is a very attractive orthopedic biomaterial compared to permanent metallic alloys. However, the critical issue is that MgCa alloy corrodes too fast in the human organism. Compared to dry cutting, the synergistic dry cutting-finish burnishing can significantly improve corrosion performance of MgCa0.8 (wt%) alloy by producing a superior surface integrity including good surface finish, high compressive hook-shaped residual stress profile, extended strain hardening in subsurface, and little change of grain size. A FEA model was developed to understand the plastic deformation of MgCa materials during burnishing process. The measured polarization curves, surface micrographs, and element distributions of the corroded surfaces by burnishing show an increasing and uniform corrosion resistance to simulated body fluid.

Evolution and empirical modeling of compressive residual stress profile after milling, polishing and shot peening for TC17 alloy

Compressive residual stress is important to improve the fatigue life of components. This paper proposed an empirical model to predict the compressive residual stress profile induced by the integration manufacturing processes (firstly milling, then polishing, finally shot peening). An exponential decay function was used to describe the compressive residual stress profile induced by milling process. Moreover, a sinusoidal decay function was proposed to describe the compressive residual stress profile induced by shot peening process. The integration manufacturing processes model was a deterministic function of the combination of exponential decay function, sinusoidal decay function, and their interaction term. Additionally, an impact coefficient was introduced to describe the influence of polishing process on compressive residual stress profile. The coefficients of the proposed models were related to the input machining parameters. Experiments of TC17 alloy were carried out utilizing response surface methodology and full factorial design to construct these models. Flank wear, tool inclination angle, axial depth of cut, shot peening intensity, and shot peening coverage were selected as five input machining parameters. According to the experimental results obtained, the evolution of compressive residual stress profile after the integration manufacturing processes was investigated, and the proposed models had been developed. The empirical model was validated by two extra experiments and a significantly good prediction was achieved.

Surface Integrity and Corrosion Performance of Biomedical Magnesium-calcium Alloy Processed by Hybrid Dry Cutting-finish Burnishing

Biodegradable magnesium-calcium (MgCa) alloy is a very attractive orthopedic biomaterial compared to permanent metallic alloys. However, the critical issue is that MgCa alloy corrodes too fast in the human organism. Compared to dry cutting, the synergistic dry cutting-finish burnishing can significantly improve corrosion performance of MgCa0.8 (wt %) alloy by producing a superior surface integrity including good surface finish, high compressive hook-shaped residual stress profile, extended strain hardening in subsurface, and little change of grain size. The measured polarization curves, surface micrographs, and element distributions of the corroded surfaces by burnishing show an increasing and uniform corrosion resistance to simulated body fluid.

Fatigue Resistance Study of Quenched and Tempered High-Strength Steel Submitted to Low Intensity Shot Peening Treatments with Different Types of Shots

The aim of this research is to study the fatigue life enhancement produced in quenched and tempered AISI4340 steel with a tensile strength of 2000 MPa after being submitted to shot peening surface treatments. These treatments generate compressive residual stress fields in a superficial layer of the material at the same time as inducing some kind of damage on the surface. Different kind of projectiles were chosen to perform the treatment (ceramic and steel shots), studying the way these affected the fatigue life of the specimens. The surface topography of the samples was analysed using a roughness tester and by means of scanning electron microscopy (SEM). The compressive residual stress profile induced by these treatments was measured using X-ray diffraction (XRD) plus electro-polishing. The fatigue behaviour of the treated samples was subsequently studied by means of 4-point rotating bending tests and their fracture surfaces were analysed using SEM. The best fatigue performance was obtained after shot peening with ceramic beads under 8A Almen intensity. The main difference in relation to the treatment performed under the same intensity but using steel cut wire shots was the much lower surface damage induced by the impacts with the ceramic shots compared with the cut wire projectiles, which in turn is justified by the greater geometric perfection and hardness of the former. Furthermore, fatigue specimens shot peened with ceramic beads under 8A intensity always gave rise to internal fatigue crack initiation, which took place outside the zone subjected to residual compressive stresses. Moreover, fatigue initiation was always linked to the presence of hard and rigid alumina inclusions, which acted as microstructural stress concentrators.

Optimization of Process Parameters of Shot Peening Using ABQUS

This paper involves an elastoplastic numerical approach to investigate effects of process parameters of Shot Peening process. The process produces compressive residual stress at the surface of treated components. It can prevent the propagation of fatigue cracks which results in an extension of fatigue life. The magnitude and depth of the compressive residual stress profile directly related to the effectiveness of the retardation of the fatigue cracks propagation. Surface material response on the development of subsurface residual stress on hardened 4340 steel surface using cast steel shots of 50 mm diameter at 67 m/s impact speeds is analysed. Simulations were carried out using ABAQUS software and it was used to model the jobs, pre-processing and post processing. The modelling involved building parts, defining materials and section, applying boundary conditions and pre-defined fields and meshing. As a result, for effective shot peening the shot direction should be kept as normal to the surface as possible by rotating the nozzle when a curved surface is to be shot peened.

Introduction of Enhanced Compressive Residual Stress Profiles in Aerospace Components Using Combined Mechanical Surface Treatments

Mechanical surface treatments such as Shot Peening (SP) and Deep Cold Rolling (DCR) are being used to introduce Compressive Residual Stress (CRS) at the surface and subsurface layers of aerospace components, respectively. This paper investigates the feasibility of a combined introduction of both the surface and sub-surface compressive residual stress on Ti6Al4V material through a successive application of the two aforementioned processes, one after the other. CRS profiles between individual processes were compared to that of combination of processes to validate the feasibility. It was found out that shot peening introduces surface compressive residual stress into the already deep cold rolled sample, resulting in both surface and sub-surface compressive residual stresses in the material. However the drawback of such a combination would be the increased surface roughness after shot peening a deep cold rolled sample which can be critical especially in compressor components. Hence, a new technology, Vibro-Peening (VP) may be used as an alternative to SP to introduce surface stress at reduced roughness.