Neutron Diffraction Techniques Research Articles

Effects of high-energetic 3He+ ion irradiation on tungsten-based composites

The interaction of plasma and its encompassing materials with one another is one of the principle designing issues of fusion reactors. Tungsten is considered one of the primary candidate materials in fusion applications due to its superior properties. In this work, we doped vanadium carbide powders to the tungsten matrix to enhance the properties of tungsten alloys. Tungsten-based composites, which irradiated with 2.5 MeV 3He+ ions at room temperature, were analyzed by atomic force microscopy (AFM) in order to obtain surface morpohologies after irradiation. Helium ion irradiated tungsten-based composites were studied by using XRD, neutron diffraction technique, raman spectroscopy, and positron annihilation spectroscopy to reveal the microstructural changes. XRD and ND analyses clarified the changes in the crystal structures of the tungsten-based materials after He ion irradiation. The simulation of radiation damage and the calculation of displacements per atom (DPA) was also determined by the SRIM code. SRIM showed that the maximum helium concentration in the specimens takes place in the depth range of 58–65 nm. The crystallite size of tungsten-based composites slightly increased after helium ion irradiation. AFM results revealed that the maximum size of bubbles on the surface of tungsten-based composites shape under 100 nm. Positron annihilation spectroscopy studies of the specimens have been discussed before and after 3He+ ion irradiation.

Investigation of magnetic ordering and origin of exchange-bias effect in doped manganite, Sm0.4Ca0.6MnO3

We have carried out detailed investigations of magnetic ordering and the origin of exchange-bias phenomenology in polycrystalline 154Sm0.4Ca0.6MnO3 perovskite compound by employing dc and ac magnetizations, neutron depolarization, and neutron diffraction techniques. The neutron diffraction study reveals a broad charge ordering transition in the temperature range of 275–150 K, manifested by gradually varying structural distortions. DC magnetization and neutron diffraction studies infer a magnetic ordering around 110 K. Below ∼40 K, this compound exhibits a large enhancement of the magnetization and an exchange-bias effect (∼18 kOe at 5 K). The exchange-bias effect shows a characteristic temperature and cooling field dependence and a training effect. The compound undergoes a CE-type (checker-board type) antiferromagnetic (AFM) ordering of Mn3+/Mn4+ spins below 110 K. The large magnetization below ∼40 K arises from the ferrimagnetic (FIM) ordering of a minority (∼5 vol. %) non-perovskite phase of Mn3O4. The appearance of exchange bias is ascribed due to the presence of an interface, formed between the FIM (Mn3O4) phase and the main AFM perovskite phase. Our study has implications in giving new directions in the search of large exchange-bias effects in mixed FIM/AFM bulk systems.

Effects of Cation-Disordering in Si4+- Substituted Li3VO4 As a Negative Electrode for Superredox Capacitors

Introduction SuperRedox Capacitors (SRC) that combine ultrafast pseudocapacitive battery materials as positive and negative electrodes are novel energy storages with battery-like energy density and supercapacitor-like power density and durability[1]. β-Li3VO4 (LVO) shows promising characteristics as a negative electrode for SRC with regards to its high energy density, with a specific capacity of 394 mAh g-1 (two electrons reaction). In addition, LVO reacts at potentials between 0.4 and 1.3 V vs. Li+/Li, whose range is suitable for the safe operation while achieving high cell voltage[2]. We have reported that disordering all cations-orientation (Li+ and V5+) of LVO increases Li+ diffusion coefficient (D Li) from the pristine LVO by a factor of one hundred, thus facilitating faster charge/discharge reactions[3]. However, such a cation-disordered structure has durability issues because of its thermodynamic metastability over 400˚C.In this study, we introduce a novel method to enhance Li+ conductivity of LVO while maintaining a stable structure. In order to obtain the same effect of cation-disordering, not all cations but only V5+ orientation was disordered by random substitution of V5+ with Si4+. Higher thermodynamic stability over 800˚C was achieved by maintaining specific arrangement between Li+ and Mn+ (Mn+ = V5+ or Si4+). Detailed influential factors of Si4+-substitution to electrochemical performances were discussed from the crystallographic point of view. Experimental Si4+-substituted LVO was prepared by a simple powder calcination process. V2O5, Li2CO3 and SiO2 powder were sealed in a zirconia pod of a planetary ball mill (PL-7, Fritsch) and mixed them at 300 rpm for 30 min. Mixture was calcined to obtain Li3+xV1-xSixO4 (LVSiO, 0≦x≦0.4). Characterization of the crystal structure was performed using X-ray and neutron diffraction techniques. In order to estimate D Li+ in the crystal structure, we used a Galvanostatic Intermittent Titration Technique (GITT). Electrochemical performances were measured using 2032-type coin cells assembled of LVSiO and Li metal electrodes. The used electrolyte composition was a 1.0 M solution of lithium hexafluorophosphate (LiPF6) dissolved in a mixture of ethylene carbonate and diethyl carbonate (50:50 in volume ratio). Results and Discussion Si4+-substituted LVO (LVSiO) was successfully synthesized, as confirmed by both X-ray and neutron diffraction patterns, confirming crystal phase change from a β-phase (Pnm21) of pristine LVO into a high-temperature γ-phase (Pnma) of LVSiO. Rietveld analysis revealed that Si4+ randomly occupied V5+ sites, whereas, Li+ and Mn+ (M = V5+ or Si4+) arrangements were maintained. Thermal stability was confirmed by in situ powder X-ray diffraction measurements while raising temperature in Ar atmosphere; the LVSiO crystal structure remains stable up to 800ºC.Results obtained from GITT measurements showed that D Li+ was maximized at 20 at.% of Si4+ and the value was maintained up to 40 at.% (Fig. 1). The effect of Si4+ substitution on reaction mechanisms were analyzed by in situ XRD electrochemical cell measurements by comparing the crystallographic change of LVO and LVSiO while Li+ insertion/deinsertion. The obtained results confirm that LVO reacts in two-phase separated mechanism and LVSiO reacts in solid solution mechanism, which is similar changes observed in the cation-disordered LVO[2,3]. It is considered that Li+ can diffuse more smoothly in solid solution mechanism than two-phase separated mechanism, since there is no phase boundary that disturbs diffusion of Li+. The D Li+ enhancement contributed to the improved capacity retention at a high rate of 100C from 25% (LVO) to 65% (LVSiO, Si20%). The obtained results show that the improvements of D Li+ and rate capability by Si4+-substitution can be achieved, as similar effect from a fully cation-disordering, while increasing thermodynamic stability. This study suggests that the main factor of effects of cation-disordering was due to the partially disordered orientation of transition metal (V5+, Si4+) cations without Li+.

(Battery Division Technology Award Address) Exploring Stable Manganese-Based Oxides As Cathodes for Na-Ion Batteries

Sodium ion batteries (SIBs) promise the potential for large-scale grid storage, due to the high abundance and wide distribution of Na sources as compared to their lithium counterparts.1-3 Among various sodium storage cathodes, layered sodium transition metal oxides (NaxMnO2) have gained significant attention owing to their great variety of compositions, ease of scalable preparation and high reversible specific capacity. In the last several years, we have utilized different strategies such as alivovalent doping, ALD coating and controlled thermal treatments to synthesize several series of P2-type Mn-based cathodes materials and obtained promising results for future development[2-5]. For example, we propose an effective and synergetic strategy in combination of liquid N2 quenching and aliovalent doping to get new layered cathode materials [5]. As evidenced by X-ray diffraction, neutron diffraction and solid-state 23Na nuclear magnetic resonance techniques, the results reveal the significance of manipulating transition metal ions vacancies and valences to the electrochemical performance of P2-type Mn-based materials. Our results demonstrate that such a new structure significantly enhances the deliverable capacity, Na+ mobility and electronic conductivity of the materials. Furthermore, the effects of aliovalent doping elements and cooling approach on the long-range structure, local environment and electrochemical performance are comprehensively studied by comparing 15 sets of Na0.67MxMn1-xO2 materials (M = Al, Fe, Mg, Li ). The optimized Na0.67Al0.1Fe0.05Mn0.85O2 material exhibits a remarkably high initial capacity of 202 mAh g-1 among ever reported P2-type layered oxides within 2-4 V, a stable capacity retention of 81% after 600 cycles and outstanding rate capability of the specific capacity up to 122 mAh g-1 at 1200 mA g-1. In addition, some work about the air-stability of these oxides materials will be also presented.

Crystal structure of monoclinic hafnia (HfO2) revisited with synchrotron X-ray, neutron diffraction and first-principles calculations.

A study on the crystal structure of monoclinic HfO2 has been performed using synchrotron X-ray and neutron diffraction data separately, as well as a combination of both. The precision of the structural parameters increases significantly due to application of the neutron diffraction technique. The experimental oxygen positions in HfO2, derived precisely, are visualized only by semi-local density functional calculations in terms of the calculated electronic band gap, but are not captured as accurately by using hybrid functionals.

In situ neutron diffraction investigation of texture-dependent Shape Memory Effect in a near equiatomic NiTi alloy

To explore the possibility of customising the functional behaviour of NiTi shape memory alloy via controlling texture, binary Ni55Ti45 (wt.%) alloys were manufactured in as cast and hot swaged conditions, presenting contrasting initial texture and macroscopic performance. In situ time-of-flight neutron diffraction technique was employed to study the texture effect on the microstructural evolution during Shape Memory Effect (SME), and a range of properties were evaluated. It was found that (i) hot swaging process leads to change in grain morphology and increase in microstrain; (ii) thermal expansion coefficients of martensite and austenite variants were weakly affected by the texture and phase transformation constraint; (iii) significant texture effect on the elastic properties at both macro- and micro-scale was quantified by Elasto-Plastic Self-Consistent (EPSC) modelling approach, while the anisotropic elastic moduli lie within the range of single crystal state and twinned structure; (iv) texture evolution during SME is weakly related to the initial microstructure; (v) martensite reoriented so that the <010> axis became aligned parallel to the loading direction, and retained this orientation upon unloading, revealing the underlying correlation between texture evolution and detwinning. Based on the experimental results, a multi-variant model was proposed to quantify the lattice strain evolution during SME. Validity of the conceptually simple and parametrically parsimonious model was confirmed by validation against experimental data.

In situ neutron diffraction and crystal plasticity analysis on Q&P1180 steel during plastic deformation

Q&P1180 is a typical third generation of advanced high strength steel. In this paper, the microstructure evolution of the Q&P1180 steel during uniaxial tension is investigated comprehensively by using in situ neutron diffraction technique, electron backscatter diffraction (EBSD), scanning electron microscope (SEM) and the elastic-visco-plastic self-consistent with phase transformation (EVPSC-PT) model. Tempered martensite (TM) is determined as the matrix based on SEM and EBSD analysis. Tiny blocky retained austenite (RA) islands are distributed in the matrix, and transformed into martensite during deformation. Effects of phase transformation on the stress-strain response, lattice strains, diffraction intensities and texture evolution of the Q&P1180 are discussed based on experiments and the EVPSC-PT model. The progressive phase transformation from austenite to martensite is orientation-dependent, and the γ{200} orientation has the lowest stability, followed by γ{220} and γ{311} orientations. The flow stress of each phase with straining shows that the strength of RA in Q&P1180 is higher than that of TM, due to its high carbon content.

In Situ Neutron Diffraction Study of Ni Addition in Co–Re–Cr High-Temperature Alloys and Influence on Phase Transformations

The influence of Ni addition to the phase transformation in the Co–17Re–23Cr high-temperature alloy was studied using neutron diffraction techniques. Three different alloys with 8, 15 and 25% of Ni were analyzed. The Ni effect on stabilization of cubic phase of Co matrix was confirmed, and the influence on σ-phase was reported. Formation of the secondary cubic phase with the smaller cell during heating and cooling associated with the creation of Re-rich σ-phase was observed. The summary phase diagrams for heating and cooling are created to depict the overall Ni influence on Co–17Re–23Cr alloy.

Magnetic Phase Diagram of Cu4–xZnx(OH)6FBr Studied by Neutron-Diffraction and μSR Techniques*Supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0302900, 2016YFA0300500, 2018YFA0704200, 2017YFA0303100, and 2016YFA0300600), the National Natural Science Foundation of China (Grant Nos. 11874401, 11674406, 11674372, 11961160699, 11774399, 12061130200, 11974392, and 11822411), the Strategic Priority Research Program(B) of the Chinese Academy of Sciences (Grant Nos.

We systematically investigate the magnetic properties of Cu4 – xZnx(OH)6FBr using the neutron diffraction and muon spin rotation and relaxation (μSR) techniques. Neutron-diffraction measurements suggest that the long-range magnetic order and the orthorhombic nuclear structure in the x = 0 sample can persist up to x = 0.23 and 0.43, respectively. The temperature dependence of the zero-field μSR spectra provides two characteristic temperatures, TA0 and Tλ, which are associated with the initial drop close to zero time and the long-time exponential decay of the muon relaxation, respectively. Comparison between TA0 and TM from previously reported magnetic-susceptibility measurements suggest that the former comes from the short-range interlayer-spin clusters that persist up to x = 0.82. On the other hand, the doping level where Tλ becomes zero is about 0.66, which is much higher than threshold of the long-range order, i.e., ∼0.4. Our results suggest that the change in the nuclear structure may alter the spin dynamics of the kagome layers and a gapped quantum-spin-liquid state may exist above x = 0.66 with the perfect kagome planes.

L-Lysine Amino Acid Adsorption on Zeolite L: a Combined Synchrotron, X-Ray and Neutron Diffraction Study.

Combined neutron and X‐ray powder diffraction techniques highlighted the sorption capacity of the acidic L zeolite towards the L‐lysine amino acid. The role of zeolite channels in the stabilization of the lysine absorbed and the effect of water on protein structure are elucidated at atomistic level. The stabilization of the L α‐helical conformation is related to strong H‐bonds between the tail aminogroups of lysine molecules and the Brønsted acid site as well as to complex intermolecular H‐bond system between water molecules, zeolite and amino acid. This finding is relevant in the catalytic synthesis of polypeptide, as well as in industrial biotechnology by qualitatively predicting binding behaviour

Microstructure evolution in a severely cold-worked NiTi wire during ageing treatment: An in situ neutron diffraction study

Cold-worked NiTi wire was subjected to ageing treatment, during which in situ neutron diffraction technique was employed to investigate the microstructure evolution in terms of crystallinity, precipitation, texture, grain size and microstrain. It was found that both heating and rapid cooling bring about significant change in microstructure, whilst precipitation process is dominant at high temperature. Besides, the approaches to extracting microstructural information, including texture, grain size and microstrain, from individual Time-Of-Flight neutron diffraction patterns are proposed and verified.

Dynamic phase transformations in additively manufactured Ti-6Al-4V during thermo-mechanical gyrations

A complex interaction of process parameters, geometry and scan strategies in Additive Manufacturing (AM), can bring about spatial and temporal transients, i.e., Σ T (x, y, z, time), within a part. Published literature focusses on fluctuating thermal cycles on the microstructure evolution. However, the microstructural variations have not been correlated to dynamic flow behavior due to the macro- and micro-scale phenomena, i.e., accumulated plastic strains brought about by large thermal gradients, transformational strains and crystallographic misfit strains. Therefore, we studied the mechanical response of Ti6Al4V alloys produced by AM under externally imposed controlled thermo-mechanical reversals in a Gleeble® thermo-mechanical simulator. The stress-strain behaviors were correlated to phase fractions, lattice strains, and also limited information on crystallographic texture using neutron diffraction techniques at the VULCAN Beamline at SNS, ORNL and also metallographic studies. The results are discussed and rationalized based on theories of static and dynamic phase transformations.

Probing low temperature non-equilibrium magnetic state in Co2.75Fe0.25O4+δ spinel oxide using dc magnetization, ac susceptibility and neutron diffraction experiments

The low temperature lattice structure and magnetic properties of Co2.75Fe0.25O4 ferrite have been investigated using experimental results from synchrotron x-ray diffraction (SXRD), dc magnetization, ac susceptibility, neutron diffraction and neutron depolarization techniques. The samples have been prepared by chemical co-precipitation of the Fe and Co nitrates solution in high alkaline medium and subsequent thermal annealing of the precipitates in the temperature range of 473–1173 K. Rietveld refinement of the SXRD patterns at room temperature indicated two-phased cubic spinel structure for the samples annealed at temperatures 473–873 K. The samples annealed at temperatures 973 K and 1173 K (CF90) have shown single phased lattice structure. Refinement of the neutron diffraction patterns in the measurement temperature range 5–300 K confirmed the antiferromagnetic (AFM) Co3O4 and ferrimagnetic (FIM) Co2.75Fe0.25O4 phases for the sample annealed at 873 K and single FIM phase of Co2.75Fe0.25O4 for the CF90 sample. Magnetic measurements have shown a non-equilibrium magnetic structure, consisting of high temperature FIM phase and low temperature AFM phase. The magnetic phases are sensitive to magnetic fields, where high temperature phase is suppressed at higher magnetic fields by enhancing the low temperature AFM phase, irrespective of annealing temperature of the samples.

Neutron diffraction measurements of weld residual stresses in three-pass slot weld (Alloy 600/82) and assessment of the measurement uncertainty

This paper describes in detail two neutron diffraction residual stress measurements, performed on the ENGIN-X neutron scattering instrument at the ISIS facility in the UK and on the SALSA instrument at the Institut Laue-Langevin in Grenoble, France. The measurements were conducted as part of the NeT Task Group 6 (TG6) international measurement round robin on an Alloy 600/82 multi-pass weldment - a slot in an Alloy 600 plate filled with three Alloy 82 weld beads, simulating a repair weld. This alloy/weld combination is considered challenging to measure, due to the large grain size and texture in the weld, and large gradients in the stress-free lattice parameter between the parent and weld metal. The basic principles of the neutron diffraction technique are introduced and issues affecting the reliability of residual stress characterization are highlighted. Two different analysis strategies are used for estimation of residual stresses from the raw data. Chemical composition studies are used to measure the mixing of parent and weld metal and highlight the steep lattice parameter gradients that arise as a consequence. The inferred residual stresses are then compared with three sets of measurements performed on the same plate by other NeT partners on E3 at the HZB in Berlin, STRESS-SPEC at the FRM II in Munich and KOWARI in Sydney. A robust Bayesian estimation average is calculated from the combined five-instrument data set, allowing reliable best estimates of the residual stress distribution in the vicinity of the weldment. The systematic uncertainties associated with the residual stress measurements are determined separately in the weld and parent materials, and compared with those in the NeT TG4 benchmark. This is a three-pass slot-welded plate fabricated from American Iron and Steel Institute AISI 316L(N) austenitic stainless steel, and is normally considered less challenging to measure using diffraction techniques than all nickel welds. The uncertainties in the stress measurements by neutron diffraction for these two weldments seem to be comparable.

Mapping of residual stresses in as-built Inconel 718 fabricated by laser powder bed fusion: A neutron diffraction study of build orientation influence on residual stresses

Manufacturing of functional (ready to use) parts with the powder bed fusion method has seen an increase in recent times in the field of aerospace and in the medical sector. Residual stresses (RS) induced due to the process itself can lead to defects like cracks and delamination in the part leading to the inferior quality of the part. These RS are one of the main reasons preventing the process from being adopted widely. The powder bed methods have several processing parameters that can be optimized for improving the quality of the component, among which, build orientation is one. In this current study, influence of the build orientation on the residual stress distribution for the Ni-based super-alloy Inconel 718 fabricated by laser-based powder bed fusion method is studied by non- destructive technique of neutron diffraction at selected cross-sections. Further, RS generated in the entire part was predicted using a simplified layer by layer approach using a finite element (FE) based thermo-mechanical numerical model. From the experiment, the part printed in horizontal orientation has shown the least amount of stress in all three directions and a general tendency of compressive RS at the center of the part and tensile RS near the surface was observed in all the samples. The build with vertical orientation has shown the highest amount of RS in both compression and tension. Simplified simulations results are in good agreement with the experimental value of the stresses.

Advances in analysis of total uncertainties in a semi‐invasive residual stress measurement method

AbstractThe ability to characterise residual stress distribution accurately and over different length scales, particularly deep into an engineering part, plays a significant role in assessing structural integrity. Two most commonly used techniques to measure residual stress fields deep into engineering components include neutron diffraction (ND) and deep‐hole drilling (DHD). As the measurements depend on several physical quantities, they are susceptible to error. The error or uncertainties may turn substantial and compromise the suitability of the results. Although noninvasive, the neutron diffraction technique is neither readily available nor portable and is limited to approximately 60‐mm‐thick specimen; errors associated with results become unacceptable at greater flight paths. Moreover, a mock‐up representing the engineering component is normally used in the ND technique. In contrast, the DHD technique is portable and measures residual stresses with high spatial resolution. An error propagation technique was applied to develop an error analysis procedure taking into consideration various stages of the DHD method and successfully applied to different DHD measurements. An essential feature comprising the effect of plasticity due to the creation of reference hole in the DHD procedure has not yet been taken into account in the error analysis procedure. This paper briefly describes how the uncertainties due to the creation of the initial reference hole can be determined. The effect of plasticity in the drilling procedure is quantified in this study. This error is combined with other sources of error and formulated to determine the total error. An incremental DHD technique was used to measure the complex triaxial residual stress field in an as‐welded circular disc, and the measured data were used to illustrate the total error using the error analysis method developed in the study.

Effect of high magnetic field on the phase transition in Fe-24%Ga and Fe-27%Ga during isothermal annealing

The effect of a high magnetic field (25 T) on the D03 to L12 phase transformation in two Fe-Ga alloys with 24 and 27 at.% Ga during isothermal annealing at 475 °C is investigated using neutron diffraction and magnetization measurements techniques. It is proved that annealing in the magnetic field increases the amount of fcc – derived L12 phase in both samples. This effect is stronger in the Fe-27%Ga alloy as compared with the Fe-24%Ga alloy. The reasons for enhancing the D03 to L12 phase transition in the magnetic field are discussed. We suggest that the most significant increase in the transformation rate is related to a decrease in the energy barrier between the phases involved in the transformation process.

Heterogeneous magnetism and kinetic arrest in antiperovskite Mn3−xNixGaC compounds with Ni2MnGa Heusler insertions

Mn-based antiperovskite compounds in the form ${\mathrm{Mn}}_{3}AX$, where $A$ is a main group element and $X$ is C or N, undergo magnetostructural transitions with which these materials acquire magnetocaloric, giant magnetoresistance, and spin-transport properties, which can be modified or tailored by manipulating the compositions of numerous compounds. This enables closer investigations and better understandings of the underlying principles governing these properties. ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Ni}}_{x}\mathrm{GaC}$, which is a derivative of the prototype ${\mathrm{Mn}}_{3}\mathrm{GaC}$ antiperovskite, would normally be expected to form a cubic structure with a homogeneous composition. Contrary to this, we find that the addition of Ni leads to a heterogenous compound consisting of an antiperovskite part and a ${\mathrm{Ni}}_{2}\mathrm{MnGa}$ Heusler insertions. The system shows kinetic arrest features, which we study as a function of Ni composition using the techniques of x-ray diffraction, magnetization, and neutron diffraction under a magnetic field.

Residual Stress and Wear Resistance of HVOF Inconel 625 Coating on SS304 Steel Substrate

Inconel 625, Ni-based superalloy has been increasingly used as coatings for protecting metallic surfaces against wear, high temperatures, and corrosive environments. In this paper, the investigation of depositing Inconel 625 of varying coating thicknesses (250, 300, 400, and 500 µm) using high-velocity oxy-fuel technique on 304 stainless steel substrate was conducted. The residual stresses of the as-sprayed coatings were investigated using neutron diffraction technique as it can provide high resolution, penetration depth, and its insensitivity to the surface condition. Friction coefficient and wear of the coating were also determined using a ball on disk tribometer sliding against E52100 steel balls. The effect of coating thickness and loading force on the tribological behavior of Inconel films were considered. Compressive residual stresses measured by neutron diffraction were observed for all coating thicknesses, particularly the 400 µm thick coating having the highest compressive stress of − 330 ± 40 MPa. The wear results suggested that the load and coating thickness has a significant influence on the wear rate and the wear mechanism on the surface, which were distinctly discussed.

Thermo-mechanical simulation of overlaid layers made with wire + arc additive manufacturing and GMAW-cold metal transfer

A thermo-mechanical simulation of the wire + arc additive manufacturing (WAAM) process is presented in this work. The simulation consists in the deposition of 5 successive layers of 316 L stainless steel on a 316 L base plate. The thermo-mechanical analysis is solved in two dimensions under plane stress assumption. Nonetheless, the metal addition is taking into account in this numerical analysis. An increment of material is added at each time step. This numerical approach allows reducing the computational time. The temperature and residual stress fields are computed at each time step. Two patterns of deposition strategy are also investigated. It is shown that the longitudinal stress varies mainly along the vertical axis. A sample with 5 overlaid layers has been scanned with neutron diffraction technique in order to measure the final residual stresses. Both numerical and measured residual stresses are in good agreement. The Aster finite element software is employed for the numerical analysis.