Residual Stress Depth Profiles Research Articles

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Turning experiments have been carried out with the cutting speed and feed as variables that were systematically varied between 10 m min-1 and 1200 m min-1, and 0.1 mm and 0.5 mm, respectively, whil ...

Analysis of Multiaxial Near-Surface Residual Stress Fields by Energy- and Angle-Dispersive X-ray Diffraction: Semi- Versus Nondestructive Techniques

Abstract Under laboratory conditions while applying angle-dispersive X-ray diffraction, the information depth in steel is usually restricted to less than 10 μm. Access to residual stresses induced by mechanical, chemical, or both types of surface treatment in deeper regions requires either the application of the layer removal method or an analysis with highly penetrating X rays and synchrotron radiation, respectively. Successive layer removal yields the actual residual stress depth profiles σij(z) up to any depth below the surface, but this is time consuming and semidestructive. High-energy X-ray diffraction performed in the energy-dispersive mode avoids these drawbacks, but it provides only the Laplace stresses, σij(τ), which have to be transformed back into the real space in order to obtain the actual stress-depth profile σij(z). Using an example of a uniaxially ground steel specimen, it is shown that the layer removal method and the energy-dispersive diffraction method for X-ray stress analysis when performed in reflection geometry yield comparable results in the case of the in-plane stress components σ11 and σ22. However, significant differences were observed concerning the out-of-plane stresses, which can be attributed to the boundary conditions that the σi3 components must satisfy at the free surface. It is demonstrated that stress redistribution at the newly generated surfaces after successive layer removal leads to an underestimation of the shear stresses σ13. The analysis of the out-of-plane normal stress component σ33 is shown to require nondestructive measurements.

Inversion procedure for dual-mode electromagnetic nondestructive characterization of shot-peened IN718

The authors have recently developed a new technique for nondestructive Hall coefficient measurement based on inductive sensing of the Hall-Corbino current produced by injecting high-frequency alternating current into the component under test. This paper investigates the feasibility of separating the competing effects of near-surface residual stress and cold work in shot-peened fully hardened IN718 alloy in high-frequency dual-mode Hall impedance and eddy current conductivity measurements. For this purpose, an inversion procedure is proposed based on iterative application of a simplistic analytical approximation of the sought depth profiles. The inversion procedure was adapted to Hall coefficient depth profiling by accounting for the secondary eddy currents produced by the Hall-Corbino current at high frequencies. In order to test the accuracy of the proposed inversion procedure, representative Hall coefficient and electric conductivity distributions were selected based on typical residual stress and cold work depth profiles obtained by destructive XRD measurements. These distributions were calculated using gauge factors measured in previous studies that investigated the influence of applied elastic and plastic strain on the Hall coefficient and electric conductivity of fully hardened IN718. Numerical forward simulations were conducted to estimate the Hall impedance and apparent eddy current conductivity spectra produced by the selected elastic and plastic strain distributions. These spectra were then used as simulated “measured” data to test the inversion procedure. It was found, that the competing residual stress and cold work contributions of shot peening can be separated using dual-mode high-frequency inspection. The sub-surface peak compressive stress and half-peak depth of the residual stress profile were reproduced with less than ±50–100 MPa and ±5–10 μm errors, respectively, that is considered quite sufficient in subsurface residual stress profiling for life prediction purposes.

Experimental and numerical analysis of residual stress in carbon-stabilized expanded austenite

Expanded austenite obtained by gaseous carburizing of stainless steel was investigated with X-ray diffraction to determine composition-depth and residual stress-depth distributions. Avoiding ghost stress effects in the analysis of X-ray diffraction data, the obtained composition- and stress-depth profiles are in excellent quantitative agreement with those obtained with other techniques. The residual stress-depth profile was attempted calculated from the composition-depth profile assuming elastic-plastic accommodation of the lattice expansion. In the model, composition-dependence of Young's modulus, yield stress and work hardening exponent were considered. Excellent quantitative agreement was achieved between the experimental and numerical residual stress-depth profiles.

Influence of Microstructure and Shot Peening Treatment on Corrosion Resistance of AISI F55-UNS S32760 Super Duplex Stainless Steel

Shot peening is a surface process commonly used in the aeronautic and automotive industries to improve fatigue resistance. Shot peening is proven to be beneficial in the fatigue behavior of components, but rarely has its influence on wear and pitting corrosion resistance been evaluated. In this work, shot peening was performed on AISI F55-UNS S32760 super-duplex stainless steel samples previously submitted to various thermal treatments, to obtain different initial microstructures and properties. Samples have been characterized in terms of microstructure morphology, local chemical composition, microhardness of each constituent phase, and energy dissipation modes. The enhanced properties provided by shot peening has been evaluated through residual stress depth profiles and Full Width at Half Maximum (FWHM) using X-ray diffraction (XRD), surface hardness, surface roughness, and corrosion resistance through salt spray fog tests. The 1400 °C solution thermal treatment was identified as the optimum initial condition, which maximizes the advantages of the shot peening treatment, even pitting corrosion resistance. These results are related to the uniformity of austenite and ferrite in terms of microstructure morphology, micromechanical properties, and alloying elements distribution.

Strengthening mechanism and hydrogen-induced crack resistance of AISI 316L stainless steel subjected to laser peening at different power densities

Microstructural response of AISI 316L stainless steel to laser peening (LP) was examined by means of optical microscopy (OM) and transmission electron microscopy (TEM) in order to analyze the effects of LP on hydrogen-induced cracking (HIC) resistance. Depth profiles of near-surface microhardness and surface compressive residual stress (CRS) of LP treated specimens were presented respectively. Slow strain rate tensile tests were performed on the hydrogen-charged samples and their corresponding stress-strain curves as well as fracture morphologies were finally investigated in detail. The results demonstrated that LP induced a grain refinement effect on the treated surface while a maximum refining rate of 56.18% was achieved at the laser power density of 10 GW/cm2. The near-surface microhardness also exhibited an attenuation trend with the increasing depth. The surface CRS positively correlated with power density before it reached a threshold value. A special U-shaped dislocation tangle band was observed in the LP treated specimen which served as hydrogen trapping sites. The LP treated samples exhibited better toughness after hydrogen charging from both macro mechanical properties and micro fracture morphologies. LP-induced grain refinement and CRS are believed to be the main contributing factors towards inhibiting the diffusion of hydrogen atoms which ultimately leads to the reduction of the hydrogen embrittlement sensitivity of AISI 316L stainless steel.

A numerically low-cost and high-accuracy periodic FE modeling of shot-peened 34CrNiMo6 and experimental validation

This paper proposed a numerically low-cost 3D FE modeling method for multi-shot shot peening. The low computation cost and high prediction accuracy of shot peening are realized at the same time by the incorporation of random multi-shot with defined spacing between the adjacent simultaneously impinging shots, periodicity, and coverage rate of 100%. With this modeling method, one-step and dual-step multi-shot peening of 34CrNiMo6 steel target is modeled and the produced residual stress is predicted. In order to make the predicted residual stress depth profile more comparable with the measured one by XRD method, the redistribution of residual stress due to the layer removal by electrochemical polishing is simulated using Model Change technique. And the comparison between the prediction and experiment indicates that this improved 3D periodic FE modeling of multi-shot impingement provides very accurate simulation models for one-step and dual-step shot peening. It can substitute for the costly and time-consuming optimization experiments of the shot peening process, especially the multi-step shot peening process. Finally, the evolution of residual stress depth profile in dual-step shot peening process is investigated by using the simulation model and a variation of residual stress towards a more uniform distribution on the finished surface taking place in the second step is discovered by RMS analysis.

Nanoscale residual stress depth profiling by Focused Ion Beam milling and eigenstrain analysis

Residual stresses play a crucial role in determining material properties and behaviour, in terms of structural integrity under monotonic and cyclic loading, and for functional performance, in terms of capacitance, conductivity, band gap, and other characteristics. The methods for experimental residual stress analysis at the macro- and micro-scales are well established, but residual stress evaluation at the nanoscale faces major challenges, e.g. the need for sample sectioning to prepare thin lamellae, by its very nature introducing major modifications to the quantity being evaluated.Residual stress analysis by micro-ring core Focused Ion Beam milling directly at sample surface offers lateral resolution better than 1μm, and encodes information about residual stress depth variation. We report a new method for residual stress depth profiling at the resolution better than 50nm by the application of a mathematically straightforward and robust approach based on the concept of eigenstrain. The results are validated by direct comparison with measurements by nano-focus synchrotron X-ray diffraction.

INFLUENCE OF ANNEALING ON THE DEPTH MICROSTRUCTURE OF THE SHOT PEENED DUPLEX STAINLESS STEEL AT ELEVATED TEMPERATURE

The depth profiles of residual stresses and lattice parameters in the surface layers of shot peened duplex stainless steel at elevated temperature were investigated utilizing X-ray diffraction analysis. At each deformation depth, residual stress distributions in both ferrite and austenite were studied by X-ray diffraction stress analysis which is performed on the basis of the sin[Formula: see text] method and the lattice parameters were explored by Rietveld method. The results reveal that difference changes of depth residual compressive stress profiles between ferrite and austenite under the same annealing condition are resulted from the diverse coefficient of thermal expansion, dislocation density, etc. for different phases in duplex stainless steel. The relaxations of depth residual stresses in austenite are more obvious than those in ferrite. The lattice parameters decrease in the surface layer with the extending of annealing time, however, they increase along the depth after annealing for 16[Formula: see text]min. The change of the depth lattice parameters can be ascribed to both thermal expansion and the relaxation of residual stress. The different changes of microstructure at elevated temperature between ferrite and austenite are discussed.

Quantitative estimation of nonmonotonic residual stress depth-profiles using an extended Kypris-Jiles model of the magnetic Barkhausen noise spectrum

Using nondestructive techniques to quantitatively estimate residual stresses along the depth is necessary to improve the ability to predict the real fatigue life of pieces for many applications. Magnetic Barkhausen noise has been proven to successfully estimate the residual stress at the surface produced by machining, plastic deformation, phase transformation or surface treatments such as shot peening, also allowing one to obtain information of the residual stress depth-profile in shot peened pieces which presented similar depth-profile shapes. However, residual stress depth-profiles with nonmonotonic or different shapes have not been successfully estimated. In the present study, an extended approach is developed in order to estimate these stresses independent of the shape of the residual stress depth-profile. The approach proposed here improves an existing model of the Barkhausen noise spectrum (Kypris-Jiles model) by adding the effect of the attenuation of the applied magnetic field on the Barkhausen noise. This extended approach is used to estimate the residual stress depth-profiles of samples with different depth-profiles using a calibration process. The approach is validated by estimating the residual stress depth-profiles, with errors smaller than 70 MPa in a depth of 130 μm, in all the samples studied.

Matching in-situ and ex-situ recorded stress gradients in an AlxGa1 − xN Heterostructure: Complementary wafer curvature analyses in time and space

In-situ wafer curvature measurements and ex-situ ion-beam layer removal method are used to evaluate residual stress depth profiles in a 1.8μm thick AlxGa1−xN heterostructure on Si(111) by evaluating substrate surface curvatures and deflections of stepwise ion-beam milled micro-cantilevers, respectively. Both approaches reveal oscillatory stress depth gradients which correlate excellent in their depth alternations. Differences are found locally in the magnitudes of the stress concentrations, especially in the regions with relatively large stresses, inhomogeneous microstructures and at relatively small thicknesses. The discrepancies are interpreted by local stress relaxations in the growing heterostructure, like dislocation formation and overgrowth by differently stressed regions.

Influence of pre-machining on the surface integrity after processing by mechanical surface treatment

The functional performance of workpieces is strongly influenced by the surface and subsurface properties which are affected and can be adjusted by manufacturing processes. The finishing process determines the final form and the surface roughness of a machined component. Nonetheless, the final surface integrity is a result of the total material modification along the whole process chain. Previous manufacturing processes affect the initial residual stress state and the work hardening in the subsurface layers. Furthermore, the resulting material modifications may vary depending on the initial or pre-machined material state. In this paper, the influence of pre-machining processes on the resulting surface integrity after mechanical finishing processes is analyzed. As finishing processes, deep rolling and so called “grind-strengthening” with varied process parameters are chosen. The initial material state is generated by heat treatment followed by pre-machining using three different processes: turning, grinding and electrochemical etching leading to strong variations in the surface-near properties. For the analysis of the influence of initial material state residual stresses as well as the shear stress were considered. Both processes, deep rolling and grind-strengthening, achieve comparable compressive stresses at the surface, whereby the residual stress states can deviate for constant parameters under variation of pre-machining. The residual stress depth profiles show a significant influence of the initial state for the grinding process but minor influence for deep rolling. The investigations contribute to a better understanding of mechanisms causing material modification during mechanical surface treatment and along the process chain.

Monitoring near-surface depth profile of residual stress in weakly anisotropic media by Rayleigh-wave dispersion

Herein we study the inverse problem on inferring depth profile of near-surface residual stress in a weakly anisotropic medium by boundary measurement of Rayleigh-wave dispersion if all other relevant material parameters of the elastic medium are known. Our solution of this inverse problem is based on a recently developed algorithm by which each term of a high-frequency asymptotic formula for dispersion relations can be computed for Rayleigh waves that propagate in various directions along the free surface of a vertically-inhomogeneous, prestressed, and weakly anisotropic half-space. As a prime example of possible applications we focus on a thick-plate sample of AA 7075-T651 aluminum alloy, which has one face treated by low plasticity burnishing (LPB) that induced a depth-dependent prestress at and immediately beneath the treated surface. We model the sample as a prestressed, weakly-textured orthorhombic aggregate of cubic crystallites and assume that by nondestructive and/or destructive measurements we have ascertained everything about the sample, including the LPB-induced prestress, before it is put into service. Under the supposition that the prestress be partially relaxed but other material parameters remain unchanged after the sample undergoes a period of service, we examine the possibility of inferring the depth profile of the partially relaxed stress by boundary measurement of Rayleigh-wave dispersion.

Residual stress formation after re‐contouring of micro‐plasma welded Ti−6Al−4 V parts by means of ball end milling

AbstractDuring the regeneration of damaged components such as compressor blades, the weld repair is followed by machining processes. Excess weld material is removed in a cutting process in order to reproduce the final contour. Therefore, both processe have to be considered regarding the resulting surface and functional properties of the repaired component. In this study, bead on plate welds are produced on 10 mm Ti‐6Al‐4 V sheets using micro‐plasma welding with different levels of welding current. They are subsequently re‐contoured via ball end milling using tools of different cutting edge radii. The residual stress depth profile is measured using X‐ray diffractometry. It is shown that the final residual stress depth profile is mainly influenced by the milling process when machining with rounded cutting edges.

Effect of Process Parameters on Distortion and Residual Stress of High-Pressure Die-Cast AZ91D Components

This paper presents a study of distortion and residual stress within a high-pressure die-cast AZ91D component, cast under different processing conditions. The influence of process parameters, i.e., die temperature, cooling time, intensification pressure and first-phase injection speeds, was examined. Distortions were measured using the in-house standard analog quality control fixture. Residual stress depth profiles were measured using a prism hole-drilling method. It was found that the most important process parameter affecting the distortion was intensification pressure and the second most important was temperature difference between the two die halves (fixed and moving side). Tensile residual stresses were found very near the surface. Increasing the intensification pressure resulted in an increased level of tensile residual stresses.

Residual stress analysis of energy-dispersive diffraction data using a two-detector setup: Part I — Theoretical concept

A new goniometer setup for energy-dispersive X-ray diffraction is introduced which is based on simultaneous data acquisition with two detectors D1 and D2, both of them freely movable in a horizontal as well as in a vertical plane. From the multitude of measurement configurations that can be realised with this setup, we figured out three efficient concepts which aim at the fast analysis of residual stress depth profiles by combining the diffraction data gathered with the two detectors. The characteristic feature of the first two configurations consists in the vertical (horizontal) positioning of the first (second) detector, which results in a diffraction geometry where the two scattering vectors span a plane that coincides with the X-circle used for sample tilt. Because each detector does see the sample under another viewing angle, both the positive and the negative ψ-branch are covered by just one χ-tilt between 0°and 90°(configuration 1) and 0°and 60°(configuration 2), thus allowing for the simultaneous analysis of the in- and out-of-plane residual stress depth gradients σiiτ and σi3τ (i=1,2), respectively, from data sets dD1hklχ and dD2hklχ. The third configuration introduced in this paper is based on a ϕ-rotation of the sample under a constant tilt angle χ and enables a fast and reliable tracing of shear stress fields σi3τ (i=1, 2).

Characterization of simultaneous aged and plasma nitrided 17-4 PH stainless steel

Microstructural characteristics (using TEM, SIMS, SEM, optical profilometry and XRD) and residual stress (using nanoindentation and XRD) of simultaneously aged and plasma nitrided martensitic 17-4 PH stainless steel were investigated. It was observed that morphology and microstructure produced during plasma nitriding of 17-4 PH stainless steel were very dependent on the treatment temperature and time. An unetchable nitrided layer formed on specimen surface nitrided at 400°C which contained expanded martensite, whereas nitrided layers at 450 and 500°C contained dark phases of nitrides in addition to expanded martensite. Nitride precipitates and expanded martensite laths were observed in TEM images and their corresponding diffraction patterns. Lack of incoherent copper rich precipitates in TEM confirmed that aging and plasma nitriding were performed simultaneously. SIMS profiles revealed that the total diffusion depth of nitrogen is 3–4 times thicker than the nitrided case. The lowest and highest surface residual stresses were contributed to PN400C5h and PN400C10h, respectively. Although hardness values increased by increasing temperature/time of plasma nitriding process, i.e. increasing nitrided layer thickness, residual stress was a function of residual stress relaxation at high temperature in addition to thickness of nitrided layer. Residual stress depth profile showed that maximum compressive residual stress at the surface, dropped to zero just below the nitrided case, then increased to a maximum value of tensile residual stress; then decreased gradually to zero. Hardness depth profile measurements revealed that hardness was very dependent on residual stress induced by nitrogen atoms diffused interstitially during plasma nitriding. Core hardness of specimens made it evident that aging took place during plasma nitriding.

Uncertainty of the X-ray Diffraction (XRD) sin2 ψ Technique in Measuring Residual Stresses of Physical Vapor Deposition (PVD) Hard Coatings

Residual stresses of physical vapor deposition (PVD) hard coatings can be measured using X-ray diffraction (XRD) methods under either conventional d-sin2 ψ mode or glancing incident (GIXRD) mode, in which substantial uncertainties exist depending on the applied diffraction parameters. This paper reports systematic research on the effect of the two analytical modes, as well as the anisotropic elastic modulus, on the measured residual stress values. A magnetron sputtered TiN grown on hardened tool steel was employed as the sample coating, to measure its residual stress using various diffraction peaks from {111} to {422} acquired at a range of incident glancing angles from 2° to 35°. The results were interpreted in terms of the effective X-ray penetration depth, which has been found to be determined predominantly by the incident glancing angle. In the d-sin2 ψ mode, the results present an approximate residual stress over a depth of effective X-ray penetration, and it is recommended to use a diffraction peak of high-index lattice plane from {311} to {422}. The GIXRD mode helps determine a depth profile of residual stress, since the measured residual stress depends strongly on the X-ray penetration. In addition, the anisotropy of elastic modulus shows limited influence on the calculated residual stress value.

Non-Destructive Determination of Residual Stress Depth Profiles of Hybrid Components by Energy Dispersive Residual Stress Measurement

Through the combination of two or more materials to one compound, for example high-strength steel and aluminum, hybrid massive components can be manufactured, whose properties are specially adapted to the respective application. One of the challenges is the joining zone which is influenced by machining induced residual stresses. In order to examine the residual stress modifications by the machining process and in addition to analyze the influence of these residual stress gradients on the lifespan of hybrid components a non-destructive method of measuring depth-resolved residual stress is necessary. Therefore, an innovative energy dispersive X-ray measurement technique is used in the collaborative research center 1153 (CRC 1153). In this study the suitability of the method is examined by comparing the results with the angle dispersive method both in machined front surface of mono materials and hybrid shafts. A parametrical study shows the possibility to get greater depth information by variation of the measuring parameters Bragg angle, tilting angle, collimator and current. In addition, the results of the energy dispersive method combined with electrolytic removal is shown. Based on these results the evaluation of the reliability and reproducibility of energy dispersive residual stress measurements is completed.

Comparison of Electronic Speckle Laser Interferometry Hole-Drilling and X-ray Diffraction Techniques for Determination of Residual Stresses in the Heat Treated Steels

Carburizing is widely used to improve wear resistance and fatigue life of high duty machine parts. Fatigue performance of the carburized components is greatly dependent on the residual stress state in the surface layer. The aim of this paper is to measure the depth profiles of residual stresses in the carburized steels by electronic speckle laser interferometry (ESPI) assisted hole-drilling, and to compare the results with those measured by X-ray diffraction technique. To comprehend the differences in the residual stress state, the low-C steel components were carburized, and then, tempered in the range of 180–600 $$^{\circ }$$ C. Microstructural investigations and hardness measurements were also conducted. The results obtained from both techniques gave identical results, and showed that the beneficial compressive residual stresses exist at the surface after carburizing, and their magnitudes decrease with increasing tempering temperature. It was concluded that ESPI assisted hole-drilling, with optimized drilling and stress calculation parameters, is suitable for determining the residual stress state of the carburized and tempered steels.