X-ray Residual Stress Research Articles

Analysis of shot-peening and residual stress relaxation in the nickel-based superalloy RR1000

This work assesses the residual stress relaxation of the nickel-based alloy RR1000 due to thermal exposure and dwell-fatigue loading. A number of different characterization methods, including X-ray residual stress analysis, electron back-scattered diffraction, microhardness testing and focused ion beam secondary electron imaging, contributed to a detailed study of the shot-peened region. Thermal exposure at 700°C resulted in a large reduction in the residual stresses and work-hardening effects in the alloy, but the subsurface remained in a beneficial compressive state. Oxidizing environments caused recrystallization in the near surface, but did not affect the residual stress-relaxation behaviour. Dwell-fatigue loading caused the residual stresses to return to approximately zero at nearly all depths. This work forms part of an ongoing investigation to determine the effects of shot-peening in this alloy with the motivation to improve the fatigue and oxidation resistance at 700°C.

A study on electric properties for pulse laser annealing of ITO film after wet etching

The electric properties of ITO thin film after UV or IR laser annealing and wet etching was analyzed via grazing incidence in-plane X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectra and residual stress measurement. The laser annealing process readily induced microcracks or quasi-microcracks on the ITO thin film due to the residual tension stress of crystalline phase transformation between irradiated and non-irradiated areas, and these defects then became the preferred sites for a higher etching rate, resulting in discontinuities in the ITO thin film after the wet etching process. The discontinuities in the residual ITO thin film obstruct carrier transmission and further result in electric failure.

Residual stress change with time of a segmented-in-series solid oxide fuel cell using an in situ X-ray stress measuring method

The changes with time of the residual stress on the electrolyte were measured in situ during re-oxidation under solid oxide fuel cell (SOFC) operation conditions using a segmented-in-series (SIS)-type SOFC and a conventional anode-supported planar (ASP)-type SOFC to understand the mechanical behaviour of the materials in the SOFC. In situ X-ray residual stress measurement was successful, and the real-time change with time of the residual stress of the electrolyte was revealed under SOFC operating conditions. In the ASP-type SOFC, the residual stress changed from compression to tensile stress, and destruction of the cell was confirmed 20 min after the air introduction. In contrast, in the case of the SIS-type SOFC, the residual stress was almost constant, even when the anode material was exposed to oxidation conditions for more than 4 h. These results indicate that the SIS-type SOFC has a high tolerance against reduction and oxidation (redox) compared with the ASP-type SOFC, which requires a conductive support material with a high Ni content. This is because the SIS-type SOFC has an electrically insulated support material that does not require a high Ni content.

X-ray Residual Stress Analysis of Nitrided Low Alloyed Steels

AbstractResidual stress analyses were performed on nitrided, low alloy steels by varying the measuring conditions. The measurements were carried out in the compound layer on ∊-Fe2–3N and γ′-Fe4N as well as in the diffusion layer on α-Fe. By considering different criteria, tensile residual stresses of up to 300 MPa produced, {111}-interference, for ∊-Fe2–3N using CuKα radiation on the specimen's surface. After removing 5 μm from the surface, compressive residual stresses occur in this phase. On employing the CrKα and CuKα radiation, relatively high compressive stresses are obtained of up to above −1000 MPa for γ′-Fe4N. For measurements using CrKα radiation, compressive residual stresses result in the diffusion layer for α-Fe, which have a maximum value below the surface. Here, the measurements of the {211}-interference give lower residual stress magnitudes than measurements of the {110}- and {200}-interferences. By verifying the phase superpositions, the linear distributions of line positions or the comparable loading stress analysis using XRD or strain gauges, the results determined at the {211}-interference appear to be realistic. Attention should be paid to the high penetration depth of CrKα radiation. Here, no gradients of the investigated stress states may exist which are too large. The steel possessing a higher content of nitride forming elements such as Al, for example, mainly exhibit the highest compressive residual stresses. In the diffusion layer of 34CrAlNi7-10, maximum compressive residual stresses of −800 MPa result at {211}-interference in α-Fe.

Fretting wear behaviour of surface mechanical attrition treated alloy 718

Alloy 718 was subjected to surface mechanical attrition treatment (SMAT) using SAE 52100 steel balls of a 5mm diameter for four different treatment durations (15, 30, 45 and 60min). Fretting wear tests were conducted at different normal loads on untreated and treated samples for 25,000cycles using alumina as a counterbody material. Microstructural features of the surface layer of samples treated by SMAT were characterized by cross-sectional optical microscopy and transmission electron microscopy. Hardness, surface roughness and residual stress were determined using a nano-indenter, surface roughness tester and X-ray residual stress analyzer respectively. SMAT resulted in the formation of nanocrystallites on the surface and near surface regions, increased hardness, increased surface roughness and compressive residual stress at the surface. Treated samples exhibited lower tangential force coefficient (TFC) compared to untreated samples. Samples treated for 60min exhibited higher grain refinement, higher hardness, lower surface roughness and higher TFC compared to the samples treated for 30min. The wear volume and wear rate of samples treated for 30min were lower compared to those of the untreated samples, which may be attributed to an optimum combination of hardness and toughness and a low work hardening rate of the nanocrystalline structure at the surface of the treated samples. In contrast, the wear volume and wear rate of the samples treated for 60min were higher than those of untreated samples, presumably due to the higher hardness and reduced toughness of the samples treated for 60min.

Thermal Relaxation Behavior of Residual Stress and Microstructure in Shot Peened S30432 Steel at Elevated Temperatures

The thermal relaxation behavior of residual stress and microstructure at elevated temperatures in S30432 austenite steel after shot peeningwas investigated by X-ray residual stress analyzer. The effect of the exposure time and the applied temperature on the residual stress andmicrostructure relaxation was particularly analyzed and discussed. A significant decrease of the residual stress values and peak breadth wasobserved in the first period of exposure time, followed by slowing down and then stabilization. It was also observed that a higher appliedtemperature produced greater relaxation. The relaxation behavior could be described by Zener­Wert­Avrami function. The thermal stability ofmicrostructure was higher than that of the residual stress. Both of the activation enthalpy of residual stress and microstructure relaxation werehigher than that of iron self-diffusion in £-Fe. [doi:10.2320/matertrans.M2012058](Received February 15, 2012; Accepted March 26, 2012; Published May 25, 2012)Keywords: thermal relaxation, residual stress, microstructure, S30432 austenite steel

ばね及びばね鋼の X 線残留応力測定法

ばね及びばね鋼の X 線残留応力測定法

Comparison of X-ray residual stress measurements for rolled steels

Residual stress occurs in almost every processing such as casting, rolling, molding, welding, and mechanical processing. A high residual stress level can significantly increase the risk of unexpected product failure from various boundary conditions. In particular, cyclic-dependent fatigue damage is much affected by the residual stress of components. Hence, accurately monitoring the residual stress will be very useful to maintain safety and to predict the repair period and the remaining life of products. X-ray diffraction is a common nondestructive technique that can be used to determine the levels of residual stress in near-surface layers of a component. Therefore, in this study, residual stress distribution in plate-type specimens of rolled steel sheets was measured by the X-ray stress measurement method. The degrees of elastic and plastic deformations were estimated by using Cr-Kα and Mo-Kα1 characteristic X-rays on SPHD and SPCD steels.

Effect of EDM Conditions on Surface Residual Stress of Cr12MoV Steel

In this paper, surface residual stress in the cold working tool steel (Cr12MoV) by EDM was investigated by X-350 X-ray residual stress analyzer and method of DJP-2 electrolytic polishing instrument to remove layer by layer in the different EDM conditions. The results show that the distribution of surface residual stress generated not only by the peak discharge current and pulse width, but also by pulse interval. The same depth from the surface, residual stress of material after hardening is larger than the residual stress after annealing, With the different combination of tool electrode and work-piece material, the form of the discharge between two electrodes and the proportion of energy put between two electrodes are different, surface residual stress are also different. Different processing liquid for processing, the depth of residual stress generated is much the same, but closer to the surface, the worse the cooling capacity (quench degrees) and surface physical properties of processing fluids, the greater the residual stress. EDM, the generation and control of the surface residual stress depends on the choice such as processing power criteria, work-piece material, electrode materials and processing liquid. Surface residual stress after processing can be used to eliminate high-temperature heat treatment.

Accuracy improvement of X-ray residual stress measurement in welds of Ni based alloy by two-dimensional detector with multiaxial rocking

In materials such as Ni based alloys, the microstructures are formed by monophase solidification without solid state transformation. It is difficult to obtain the welding residual stress by X-ray diffraction because of the preferred orientation of the unidirectional solidification and the grain growth in the heat affected zone. To exclude their effect, a method that records the diffraction peaks in a two-dimensional detector combined with multiaxial rocking is proposed. It is clarified that the equilibrium of shrinkage and the recovery of strain during the thermal cycle determines the site of the maximum tensile stress. In addition, dynamic recrystallisation, which occurs during welding, contributes to the decreased residual stress at the fusion line. If the spatial resolution of the proposed and the conventional measurement methods can be correlated, the results of each method agree well. Therefore, the proposed method is an effective tool for measuring the residual stress in welded joints of Ni based alloy.

Unusual Structure and Fabrication Process of Japanese Matchlock Gun (Hinawajuu), Made at the Late EDO Period

The metallurgical macro- and micro-structure, and the residualstress of the Japanese matchlock gun, fabricated at the late Edo period, have been investigated with an optical microscope, an SEM, an EPMA and an X-ray residual stress meter for estimating the fabricating process and their materials. This gun was fabricated by Udonbari (in Japanese) process, which is similar to that of the Russell's method, tubes was created by the joining together opposite edges of a flat iron strip with an iron core bar. The joining line was wavy. Their residual stress was mainly compressive and the values were from 180 to 280 MPa in the longitudinal direction and from 240 to 380 MPa at the transverse direction.The gun was made of low carbon steel with equiaxed ferrite grains; their grain size was mainly 10 μm partly with 100 μm and exceptionally more than 1000 μm grains. Moreover, we find the special banded structure, consisted of fine ferrite grains bands and large ferrite grains bands.The firing part was fabricated by the joining of five parts for getting the L-shape hole. The female screw was made by forging; therefore the shape was tapered screw and the male screw was cut from a low grade steel bar, confirmed by their macro-structure.

Residualstressanalysisofshot-peenedaluminumalloybyfineincrementhole-drillingandX-raydiffractionmethods

This paper proposes an analysis of the fine-increment hole-drilling and of the x-ray diffraction methods for residual stress measurement. This analysis was carried out on some shot-peened aluminum alloy samples, with particular attention to the surface. The shot-peening treatment introduces high compressive stress close to the surface of the sample, and for this reason it is widely used to extend the fatigue life of many mechanical components. The hole-drilling method is based on the measurement of the surface strain relaxed during the incremental drilling of a small hole in the material. According to the ASTM E837-08 standard, the residual stress distribution can be measured over a typical depth of 1mm. X-ray residual stress analysis is based on the evaluation of interplanar distances in deformed samples along different orientations. This technique is suitable for the surface region, typically 10-40 |xm. In-depth stress evaluation can be obtained by progressively thinning the sample and collecting diffraction patterns after each step. The results obtained with the two methods are discussed, considering the different sources of uncertainty, to check the effectiveness of the two methods for the study of this class of materials.

ステンレス鋼およびアルミニウム合金のバニシング加工による<br>表面改質における最適加工条件と表面層の機械的性質

This study deals with a surface modification phenomenon in a cylindrical surface finishing process using diamond burnishing tools. The burnishing process is a micro-plastic machining method, in which a spherical diamond point tool compresses the metal surface to obtain a mirrorlike surface roughness; it could improve surface layer hardness similarly to the shot-peening process. In this report, we try to evaluate the surface modification in the burnishing process using the nanoindentation technique and an X-ray residual stress measuring instrument owing to the extremely thin surface layer. From the experimental result, the hardness of the surface layer is improved (by at least 100 HV) and a significant residual stress (-700MPa) remains on the surface layer of the burnished workpiece.

An Evaluation of the Use of X-ray Residual Stress Determination as a Means of Characterizing Oxidation Damage of Nickel-Based, Cr2O3-Forming Superalloys Subjected to Various Oxidizing Conditions

The use of X-ray residual stress determination as a technique for evaluating the damage incurred by nickel-based, Cr2O3-forming superalloy materials under various service conditions (isothermal heating, thermal cycling, applied stress, stressed and cycled) was investigated. Large and small compressive residual stresses were observed for the oxides and the near surface substrates, respectively. It was expected that the applied stresses and thermal cycling would cause an enhanced degree of oxidation damage that would translate into appreciable differences in residual stress values. Differences in the magnitude of residual stress values were not appreciable condition-to-condition, however. An increase in the severity of the oxidizing conditions in the form of longer oxidation times, higher oxidizing temperatures, and a much greater frequency of thermal cycling is suggested for future studies.

Prediction of residual stresses in thermally sprayed steel coatings considering the phase transformation effect

The present study is aimed to propose an elastoplastic bilayer model for prediction of residual stresses in thermally sprayed coatings, in which the effect caused by martensite phase transformation for steel coating materials was taken into account. Closed-form solutions of the curvature and stresses within the substrate and coating are obtained for the plastically deformed structures. Applications of the model for prediction of the twin-wire electric arc sprayed high carbon steel coatings were investigated subsequently. In the application case that a thin coating layer deposited with varying temperatures, the martensite phase transformation has a significant effect on the residual stress, e.g. a lower deposition temperature leads to more amount of martensite transformation and then to a lower level of final stress. The model was also used to predict the stress distribution of high carbon steel coating after quenching heat treatment, and the calculation results were compared with the X-ray residual stress measurements. It is found that the residual stresses on the coating surface obtained from the analytical model are closed to that obtained from the experiments.

Liquid forging of thin Al–Si structures

Liquid forging is a pressurized solidification process, wherein finished components can be produced in a single process from molten metal to solid, utilizing re-useable die tools. In conventional die casting (gravity and pressure), components with a minimum wall thickness of about 0.6 mm can be fabricated. However, parts with section thickness as thin as 0.2 mm can be liquid forged using near eutectic Al–Si or Al–Si–Cu alloys. Water based lubricant containing micrographite is effective in releasing the component during ejection. In addition, it aids in shaping the component to required dimensional accuracy. These liquid forged parts are pore free. Thermal analysis of liquid forged 0.8 mm plate revealed rapid freezing at the rate of about 700 °C/s. During the process, die and punch were maintained at 200–250 °C. X-ray residual stress analysis on the surface of the liquid forged plate showed high intensity values for 0.1 mm plate. Distribution of eutectic silicon at inter dendritic region is extremely fine to nanoscale level.

X-ray Residual Stress Measurement of Fiber Reinforced Plastic Composite

In this study, the residual stresses in high-density polyethylene (HDPE) and a fiber reinforced polyethylene was measured using an x-ray stress measurement technique. There have been few reports published of residual stress investigations in polymeric materials by x-ray stress measurements based on conventional x-ray reflection methods. There are two problems associated with this measurement. Firstly, the diffraction peaks of the polymer appear in the low 2θ angle region and therefore the measurement accuracy for strains reduces. Secondly, the low 2θ angle region makes it extremely difficult to use the sin2ψ method. In the present study we tried to use a transmission method for measuring the residual stress in HDPE samples to resolve these problems. The HDPE sample is shaped into thin sheets which have the three kinds of crystallinity degrees. The measured data is fitted with a good linear regression line in a 2θ-sin2ψ diagram and the gradient of the regression line corresponded to the applied stress. On the other hand, the results of the residual stress measurement are deeply associated with degrees of the crystallinity in the HDPE material. The quantitative estimation of crystallinity degrees in the HDPE material was accomplished by a sink-float method. The residual stress distributions were discussed between micro-residual stresses in the crystal phase of HDPE with the amorphous phase of it. Finally, x-ray elastic constant (XEC) of HDPE was estimated and the residual stresses in the fiber reinforced polyethylene was also measured by use of this XEC parameter.

RESIDUAL STRESSES ON INCONEL 718 TURBINE SHAFT SAMPLES AFTER TURNING

Results of X-ray residual stress measurements on Inconel 718 turbine shaft samples are here proposed. The paper presents part of the EU STREP project VERDI activity, where the aim was to supply those who numerically simulate machining process with an experimental database of proved reliability. Measurements were planned on a set of samples machined with different levels of cutting speed and feed rate. Due attention was given to the assessment of the uncertainty of experimental results. A database of surface residual stress values and depth profiles is presented with the estimated uncertainty both on stress and depth values. The stress proved to be always tensile at the surface and compressive below the surface. Higher cutting speed and feed rates produce higher surface tensile stresses but the trends are different for the two measurement directions.

Spatial variation of residual stresses in a welded pipe for high temperature applications

Measurements of residual macro-stresses have been undertaken in a feature multipass circumferential single V butt-weld made from a P91 ferritic steel pipe over different spatial depths: (i) ≤10 μm by X-ray diffraction, (ii) ≤1 mm by incremental centre-hole drilling and (iii) through wall section using deep-hole drilling. The ability to make near-surface X-ray residual stress measurements on as-oxidised surfaces has been demonstrated and the implications for use in the evaluation of overall integrity are discussed. Each of the three measurement techniques provides complementary and consistent measurement of induced residual stresses for weld metal, heat affected zone and parent metal for the as-welded and the post-weld heat-treated conditions over the complete spatial range. The results are discussed with respect to the importance of the weld capping run in introducing near-surface compressive residual stresses, the through-wall profiles of the residual stresses measured at the weld metal position in hoop and axial directions and the presence of existing surface oxide.

Residual Stress State Characterization of Machined Components by X-ray Diffraction and Multiparameter Micromagnetic Methods

Machining induced residual stress states have been identified to affect the distortion of parts during following heat treatments. Thus, ideally a complete characterization of the components residual stress state is required. Magnetic and micromagnetic analysis of residual stresses can represent an important gain of time compared to X-ray diffraction. Investigations with these two methods were performed on different components with various and inhomogeneous residual stress states: cylindrical and tapered ball bearing rings made from AISI52100 steel and a disc made from AISI5210 steel. Reliable results and good agreement between X-ray diffraction data and residual stresses obtained from the magnetic and micromagnetic analysis can be obtained with the use of a calibration for each single component. An important gain of time can be achieved with the combined use of X-ray diffraction analysis for the calibration and the micromagnetic technique. However, local residual stress variations in zones smaller than the sensor size may not be detected. A global calibration of the micromagnetic equipment with one calibration file for several parts still needs optimization.