Showing papers on "Shot peening published in 2006"

Surface nanocrystallization induced by shot peening and its effect on corrosion resistance of 1Cr18Ni9Ti stainless steel

Abstract: The nanocrystalline microstructure in the surface of 1Cr18Ni9Ti stainless steel induced by high-energy shot peening has been characterized by means of X-ray diffractometry and transmission electron microscopy. The effects of shot peening on corrosion resistance of the steel have been investigated by polarization curves and pit corrosion tests, and the surface morphologies of the corrosion samples have been characterized by scanning electron microscopy. The results show that shot peening can cause surface nanocrystallization; that is, a nanocrystalline microstructure with an average grain size of ∼ 18 nm forms in the surface layer of the sample, and furthermore, can induce α-martensite of about 15% in volume fraction. With increasing depth from the shot-peened surface, the grain size increases, but the volume fraction of the α-martensite decreases. The surface nanocrystallization can improve the potentiodynamic polarization behavior of 1Cr18Ni9Ti stainless steel in 3.5% NaCl solution. Comparing to the as-received coarse crystalline counterpart, the passive film on the surface of the shot-peened sample is easier to form and more stable. Shot-peening-induced surface nanocrystallization can markedly enhance the corrosion resistance of 1Cr18Ni9Ti stainless steel in the chlorine–ion-contained solution.

Finite element modelling of shot peening process: Prediction of the compressive residual stresses, the plastic deformations and the surface integrity☆

Abstract: This paper presents a numerical simulation of the shot peening process using finite element method. The majority of the controlling parameters of the process have been taken into account. The shot peening loading has been characterised by using energy equivalence between the dynamic impact and a static indentation of a peening shot in the treated surface. The behaviour of the subjected material is supposed to be elastic plastic with damage. An integrated law of the damage proposed by Lemaitre and Chaboche has been used. The proposed model leads to obtain the residual stress, the plastic deformation profiles and the surface damage. An application on a shot peened Ni-based super alloy Waspaloy has been carried out. The comparison of the residual stresses, obtained by X-ray diffraction method and by finite element calculation, shows a good correlation. The in-depth profile of the plastic deformations and the superficial damage values are in good agreement with the experimental observations.

Modern Mechanical Surface Treatment: States, Stability, Effects

Abstract: 1 Introduction. 2 Procedures of Mechanical Surface Treatments. 2.1 Shot Peening. 2.1.1 Definition and Delimitation of Procedure. 2.1.2 Application Examples. 2.1.3 Devices, Tools and Important Parameters. 2.2 Stress Peening. 2.2.1 Definition and Delimitation of Procedure. 2.2.2 Application Examples. 2.2.3 Devices, Tools and Important Parameters. 2.3 Warm Peening. 2.3.1 Definition and Delimitation of Procedure. 2.3.2 Application Examples. 2.3.3 Devices, Tools and Important Parameters. 2.4 Stress Peening at Elevated Temperature. 2.5 Deep Rolling. 2.5.1 Definition and Delimitation of Procedure. 2.5.2 Application Examples. 2.5.3 Devices, Tools and Important Parameters. 2.6 Laser Peening. 2.6.1 Definition and Delimitation of Procedure. 2.6.2 Application Examples. 2.6.3 Devices, Tools and Important Parameters. 3 Surface Layer States after Mechanical Surface Treatments. 3.1 Shot Peening. 3.1.1 Process Models. 3.1.2 Changes in the Surface State. 3.2 Stress Peening. 3.2.1 Process Models. 3.2.2 Changes in the Surface State. 3.3 Warm Peening. 3.3.1 Process Models. 3.3.2 Changes in the Surface State. 3.4 Stress Peening at elevated Temperature. 3.5 Deep Rolling. 3.5.1 Process Models. 3.5.2 Changes in the Surface State. 3.6 Laser Peening. 3.6.1 Process Models. 3.6.2 Changes in the Surface State. 4 Changes of Surface States due to Thermal Loading. 4.1 Process Models. 4.1.1 Elementary Processes. 4.1.2 Quantitative Description of Processes. 4.2 Experimental Results and their Descriptions. 4.2.1 Influences on Shape and Topography. 4.2.2 Influences on Residual Stress State. 4.2.3 Influences on Workhardening State. 4.2.4 Influences on Microstructure. 5 Changes of Surface Layer States due to Quasi-static Loading. 5.1 Process Models. 5.1.1 Elementary Processes. 5.1.2 Quantitative Description of Processes. 5.2 Experimental Results and their Descriptions. 5.2.1 Influences on Shape and Deformation Behavior. 5.2.2 Influences on Residual Stress State. 5.2.3 Influences on Workhardening State. 5.2.4 Influences on Microstructure. 6 Changes of Surface States during Cyclic Loading. 6.1 Process Models. 6.1.1 Elementary Processes. 6.1.2 Quantitative Description of Processes. 6.2 Experimental Results and their Descriptions. 6.2.1 Influences on Residual Stress State. 6.2.2 Influences on Worhardening State. 6.2.3 Influences on Microstructure. 6.3 Effects of Surface Layer Stability on Behavior during Cyclic Loading. 6.3.1 Basic Results. 6.3.2 Effects on Cyclic Deformation Behavior. 6.3.3 Effects on Crack Initiation Behavior. 6.3.4 Effects on Crack Propagation Behavior. 6.3.5 Effects on Fatigue Behavior. 7 Summary. Acknowledgments. Index.

3-D FEM simulation of laser shock processing

Abstract: Laser shock processing is an innovative surface treatment technique similar to shot peening. It can impart compressive residual stresses in material for improving fatigue, corrosion and wear resistance of metals. FEM simulation is an effective method to predict mechanical effects induced in the material treated by laser shock processing. An analysis procedure including dynamic analysis performed by LS-DYNA and static analysis performed by ANSYS is presented in detail to attain the simulation of the single and multiple laser shock processing to predict the residual stress field and the surface deformation. History of the energies during dynamic analysis is analyzed and validated by the theoretical calculation. The predicted residual stress field for single laser shock processing is well correlated with the available experimental data and a homogeneous depression with little roughness modification in the action zone of the shock pressure is induced on the treated surface according to the simulation of surface deformation. Simulation of multiple laser shocks is also performed, which indicates that compressive residual stresses and plastically affected depth can be extensively increased and gradually reach the saturated state with the increase of laser shock number.

Effects of fatigue and fretting on residual stresses introduced by laser shock peening

Abstract: The effects of fatigue and fretting fatigue on the distribution of residual stresses in shot and laser shock peened Ti–6Al–4V samples have been investigated. Residual elastic strains have been determined using high-energy synchrotron X-ray diffraction. Laser shock peening introduces a considerable compressive residual stress, the compressive zone extending 1.5 mm below the surface. The effects of fatigue loading have been investigated using a notched three-point bend geometry. The residual stress field was found to be largely insensitive to fatigue cycling, at least for the applied stress range studied. For fretting fatigue, while the residual stresses at depth were little affected, within 0.5 mm of the surface significant stress relaxation was observed; the extent of relaxation being greatest in the direction parallel to the fretting direction. The states of residual stress have been quantified using the concept of eigenstrain, which quantifies the retained plastic misfit resulting from peening. Finite element modeling has been used to determine the eigenstrain profiles causing the measured elastic strain profiles, and the changes to these eigenstrain profiles due to fretting. Our results suggest laser shock peening confers much greater fretting fatigue resistance than traditional shot peening alone due to the much deeper compressive zone.

Multi-Axial Contour Method for Mapping Residual Stresses in Continuously Processed Bodies

Abstract: This paper describes a method for extending the capability of the contour method to allow for the measurement of spatially varying multi-axial residual stresses in prismatic, continuously processed bodies Currently, the contour method is used to determine a 2D map of the residual stress normal to a plane This work uses an approach similar to the contour method to quantify multiple components of eigenstrain in continuously processed bodies, which are used to calculate residual stress The result of the measurement is an estimate of the full residual stress tensor at every point in the body The approach is first outlined for a 2D body and the accuracy of the methodology is demonstrated for a representative case using a numerical experiment Next, an extension to the 3D case is given and the accuracy is demonstrated for representative cases using numerical experiments Finally, measurements are performed on a thin sheet of Ti-6Al-4V with a band of laser peening down the center (assumed to be 2D) and a thick laser peened plate of 316L stainless steel to show that the approach is valid under real experimental conditions

Improving fatigue strength of metals using abrasive waterjet peening

Abstract: Abrasive waterjet (AWJ) peening has been proposed as a viable method of surface treatment for metal orthopedic devices. In this study the influence of AWJ peening on the compressive residual stress, surface texture and fatigue strength of a stainless steel (AISI 304) and titanium (Ti6Al4V) alloy were studied. A design of experiments (DOE) and an analysis of variance (ANOVA) were used to identify the primary parameters contributing to the surface texture and magnitude of surface residual stress. The influence of AWJ peening on the fatigue strength of the metals was evaluated under fully reversed cyclic loading. It was found that AWJ peening results in compressive residual stress and is primarily influenced by the abrasive size and treatment pressure. The residual stress of the AISI 304 ranged from 165 to over 460 MPa. Using the optimum treatment parameters for maximizing the residual stress, the endurance strength of Ti6Al4V was increased by 25% to 845 MPa. According to results of this study AWJ peening is...

Behaviour of shot peening combined with WC–Co HVOF coating under complex fretting wear and fretting fatigue loading conditions

Abstract: This study investigated the fretting and fretting fatigue performance of tungsten carbide-cobalt (WC-Co) HVOF spray coating systems. Fretting wear and fretting fatigue tests of specimens with shot peening and WC-Co coatings on 30NiCrMo substrates were also performed. The WC-Co coating presents very good wear resistance by decreasing the energy wear coefficient ([alpha]) under fretting conditions by more than 9 times. The tested coating reduces crack nucleation under both fretting and fretting fatigue situations. Finally the crack arrest conditions are evaluated by the combined fretting and fretting fatigue investigation. It is shown and explained how and why this combined surface treatment (i.e., shot peening and WC-Co) presents a very good compromise against wear and cracking fretting damage.

Finite Element Simulation of Shot Peening – A Method to Evaluate the Influence of Peening Parameters on Surface Characteristics

Abstract: Shot peening, known for its potential to improve fatigue strength of metallic parts, can be seen as a multiple and progressively repeated elastic-plastic interaction between the surface and the shots. With each impact the target undergoes local plastic deformation while the shot is moving into the material. After the contact between the target and the shot has ceased, compressive residual stresses remain at the surface and small tensile residual stresses in the inside. Developing a model to analyze the process of shot peening is usefirl for several reasons; to be able to predict the material state after peening without having to conduct costly experiments and to be able to optimize peening processes. In contrast to prior studies found in the literature [I-41, a more detailed approch by simulating several single impacts on a 3-dimensional surface is chosen to model the shot peening process.

Investigation of the influence of incidence angle on the process capability of water cavitation peening

Abstract: Water cavitation peening (WCP), through the cavitation impact induced by the water jet process, has been applied to introduce the compressive residual stress in the surface layer of metallic materials. In the present study, five incidence angles (0°, 30°, 45°, 60°, and 90°) were adopted. The impact pressure induced by the bubble collapse was measured by a pressure measurement technique with pressure sensitive film. The residual stresses of a spring steel SAE 1070 plate specimen treated by WCP were determined through X-ray stress analysis. The results indicated that the impact pressure and residual stress obtained at various incidence angles were almost equal to each other in the effective process area. It implied that the process capability of WCP was almost isotropic. Moreover, such potential of WCP was also applied to a carburizing-quenched helical gear, and the high and uniform compressive residual stress was simultaneously introduced in the surface and bottom of gear tooth. It indicated that, compared with the conventional shot peening and laser shock peening, WCP was more effective to the metallic components with the complicated shape.

Strengthening of Ceramics by Shot Peening

Abstract: Shot peening is a common finishing procedure to improve the static and cyclic strength of metal components. Recent investigations showed that, under specific shot peening conditions, also in brittle ceramics high compressive stresses up to more than 1 GPa can be introduced near the surface which increase the near-surface strength. The presentation compiles the actual potential of the shot peening process for alumina and in detail for silicon nitride ceramics. The influence of shot peening parameters on the residual stress state, dislocation density, topography, static and cyclic and rolling near-surface strength is determined.

Avoiding ghost stress on reconstruction of stress- and composition-depth profiles from destructive X-ray diffraction depth profiling

Abstract: The present paper addresses the accuracy of the reconstruction of depth profiles from X-ray diffraction lattice-strain analysis, combined with successive sublayer removal. In order to test the accuracy of reconstruction irrespective of experimental inaccuracies, X-ray diffraction was simulated for model stress-depth profiles and/or composition-depth profiles, reflecting those obtainable with surface engineering of materials, i.e. shot peening, carburizing of austenite and low temperature nitriding of stainless steel. Two principally different methods for the reconstruction of the actual stress and composition profiles were compared: (I) assuming that the lattice parameter determined at a specific depth, for a specific value for ψ is a weighted average over the actual lattice spacing profile for this ψ-direction; (II) assuming that the stress/strain determined at a specific depth is a weighted average over the actual stress/strain depth profile. On the basis of the results it is concluded that method (I) virtually avoids the occurrence of ghost stresses (stress artefacts) upon data evaluation. Substantial ghost stresses may occur upon data analysis using method (II) for strongly compositionally graded materials.

Deburring and surface conditioning of micro milled structures by micro peening and ultrasonic wet peening

Abstract: Deburring and smooth finishing processes for milled workpieces are well known in macro mould and die manufacturing. These processes are not directly transferable to micro parts and must be modified for this purpose. Therefore, deburring and surface conditioning by micro peening and ultrasonic wet peening of structures made by micro milling of quenched and tempered tool steel are investigated. The results are presented in this paper.

An Analytical Model for Shot-Peening Induced Residual Stresses

Abstract: To improve the fatigue life of metallic com- ponents,especially in aerospace industry,shot peening is widely used. There is a demand for the advancement of numerical algorithms and methodologies for the estima- tion of residual stresses due to shot peening. This paper describes an analytical model to simulate the shot peen- ing process and to estimate the residual stress field in the surface layer. In this reasonable, convenient, and simple model, no empirical relation is used, and the effects of shot velocity are included. The results of validation of this model against the test data are very good. keyword: Shot-peening, Residual Stress, Analytical

Characteristics of Surface Layers Produced by Shot Peening

Abstract: Production processes, especially mechanical surface treatments like shot peening, lead to changes in the materials state close to the surface, which severely affect the success of the treatment, especially the resulting fatigue properties. Formerly these effects on fatigue life were controversely discussed as effects of mechanical workhardening, which first were postulated to be dominating by Foppl and his group [1,2], and effects of compressive residual stresses, which first were assumed to increase the fatigue properties by Thum and his group [3,4]. Additionally, effects of topography on fatigue properties were studied by Houdremont and Mailander [5] and Siebel and Gaier 161. Today it is well known that most of the changes of surface characteristics induced by shot peening which are listed in Fig. 1 and the stability of these changes may affect the fatigue properties of components and that these effects can be described in the so called concept of local fatigue properties [7,8,9]. 'Therefore the influence of process parameters of the shot peening treatments listed in Fig. 2 on the surface characteristics has to be well known. Besides the parameters concerning the peening device or the shot, the parameters concerning the workpiece are of high interest. Especially the workpiece temperature and the prestress are altered in modifications of the peening process named warm peening and stress peening which will be discussed separately. Tn some cases additional annealing treatments are used to achieve further improvements of the material state close to the surface. In the presen! paper a systematic overview of up to date knowledge about the changes in the surface state due to shot peening is given by discussing characteristic examples concerning changes of the topography, residual stress state, workhardening state and microstructure of components due to shot peening. A special focus will be drawn to the previously mentioned modifications of the conventional shot peening process like stress peening, warm peening and peening plus subsequent annealing, which show improvements in the surface properties or at least improvements of the stability of the induced surface state.

Precipitation and residual stress relaxation kinetics in shot-peened Inconel 718

Abstract: Mechanical surface treatment by shot peening followed by aging at 700 and 740 °C was performed on Inconel 718. A previously proposed XRD method (Ref 10) for the quantitative phase analysis of Inconel 718 allowed for the determination of the precipitation kinetics of the γ″ phase in the shot-peened layer and the matrix, respectively. The residual compressive stress field induced by shot peening and its relaxation behavior during aging were also determined. The relaxation process can be described by the Zener-Wert-Avrami function. The precipitation rate in the γ″ phase in the shot-peened layer is greatly accelerated, which causes differences in the γ″ phase amounts between the skin and the core during aging, especially during the initial stage. The high precipitation rate of the γ″ phase in the shot-peened layer can be interpreted by the nonequilibrium segregation of niobium.

On the Influence of Cold Work on Eddy Current Characterization of Near-Surface Residual Stress in Shot-Peened Nickel-Base Superalloys

Abstract: Shot-peened nickel-base superalloys exhibit 1–2% increase in apparent eddy current conductivity (AECC), which can be exploited for nondestructive residual stress assessment. Experimental evidence indicates that the excess AECC is due in part to elastic strains, i.e., residual stress, and in part to plastic strains, i.e., cold work. The very fact that the conductivity increases rather than decreases was originally thought to indicate that there was no significant cold work contribution to the observed AECC increase. This assumption was also supported by X-ray diffraction (XRD) results on fully relaxed specimens showing that the cold work induced widening of the diffraction beam only partially vanishes when both the residual stress and the AECC completely disappear due to thermal relaxation. However, we show in this paper that assuming that the conductivity change is entirely due to residual stress via the piezoresistivity of the material could result in an unacceptable overestimation of the magnitude of the compressive residual stress. Therefore, we investigated the different mechanisms through which cold work could influence the AECC in surface-treated nickel-base superalloys. It was found that neither the magnetic susceptibility nor the piezoresistivity of the material is affected significantly by cold work up to 50% plastic strain level, but the electrical conductivity does substantially increase due to microstructural changes. Based on these observations, we suggest that in future research the complex variations caused by cold work should be modeled by at least two main types of cold work parameters rather than by a single one in order to properly account for the otherwise contradictory effects of plastic deformation on eddy current conductivity and XRD measurements.