Convolutional Multiple Whole Profile Research Articles

Time-Dependent Evolution of Al-Al4C3 Composite Microstructure and Hardness during the Sintering Process.

In this study, Al-Al4C3 compounds were manufactured by mechanical milling followed by heat treatment. To analyze the microstructural evolution, the composites were sintered at 550 °C at different sintering times of 2, 4 and 6 h. The mechanical results suggest that dislocation density and crystallite size primarily contribute to hardening before the sintering process, with a minimal contribution from particle dispersion in this condition. The compound exhibited a significant 75% increase in hardness after 2 h of sintering, primarily attributed to the nucleation and growth of Al4C3 nanorods. The HRTEM analysis, combined with geometric phase analysis (GPA) at and near the Al-Al4C3 interface of the nanorods, revealed strain field distributions primarily associated with partial screw dislocations and the presence of closely spaced dislocation dipoles. These findings are consistent with the microstructural parameters determined from X-ray diffraction pattern analysis using the convolutional multiple whole profile (CMWP) method. This analysis showed that the predominant dislocation character is primarily of the screw type, with the dislocation dipoles being closely correlated. Based on these results, it is suggested that samples with a lower weight percentage of reinforcement and longer sintering times may experience reduced brittleness in Al/Al4C3 composites. Strengthening contributions were calculated using the Langford-Cohen and Taylor equations.

Analysis of the dislocation activity of Mg-Zn-Y alloy using synchrotron radiation under tensile loading.

An understanding of deformation behavior and texture development is crucial for the formability improvement of Mg alloys. X-ray line profile analysis using the convolutional multiple whole profile (CMWP) fitting method allows the experimental determination of dislocation densities separately for different Burgers vectors up to a high deformation degree. A wider use of this technique still requires exploration and testing of various materials. In this regard, the reliability of the CMWP fitting method for Mg-Zn-Y alloys, in terms of the dislocation activity during tensile deformation, was verified in the present study by the combined analysis of electron backscatter diffraction (EBSD) investigation and visco-plastic self-consistent (VPSC) simulation. The predominant activity of non-basal 〈a〉 dislocation slip was revealed by CMWP analysis, and Schmid factor analysis from the EBSD results supported the higher potential of non-basal dislocation slip in comparison with basal 〈a〉 dislocation slip. Moreover, the relative slip activities obtained by the VPSC simulation also show a similar trend to those obtained from the CMWP evaluation.

Microstructural and Mechanical Characterization of Al Nanocomposites Using GCNs as a Reinforcement Fabricated by Induction Sintering

High-energy ball milling is a process suitable for producing composite powders whose achieved microstructure can be controlled by the processing parameters. Through this technique, it is possible to obtain a homogeneous distribution of reinforced material into a ductile metal matrix. In this work, some Al/CGNs nanocomposites were fabricated through a high-energy ball mill to disperse nanostructured graphite reinforcements produced in situ in the Al matrix. To retain the dispersed CGNs in the Al matrix, avoiding the precipitation of the Al4C3 phase during sintering, the high-frequency induction sintering (HFIS) method was used, which allows rapid heating rates. For comparative purposes, samples in the green and sintered state processed in a conventional electric furnace (CFS) were used. Microhardness testing was used to evaluate the effectiveness of the reinforcement in samples under different processing conditions. Structural analyses were carried out through an X-ray diffractometer coupled with a convolutional multiple whole profile (CMWP) fitting program to determine the crystallite size and dislocation density; both strengthening contributions were calculated using the Langford-Cohen and Taylor equations. According to the results, the CGNs dispersed in the Al matrix played an important role in the reinforcement of the Al matrix, promoting the increase in the dislocation density during the milling process. The strengthening contribution of the dislocation density was ~50% of the total hardening value, while the contribution by dispersion of CGNs was ~22% in samples with 3 wt. % C and sintered by the HFIS method. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to analyze the morphology, size, and distribution of phases present in the Al matrix. From the analyses carried out in AFM (topography and phase images), the CGNs are located mainly around crystallites and present height profiles of 1.6 to 2 nm.

Dislocation Density of Electron Beam Powder Bed Fusion Ti–6Al–4V Alloys Determined via Time-Of-Flight Neutron Diffraction Line-Profile Analysis

Ti–6Al–4V alloys undergo a multiple phase transformation sequence during electron beam powder bed fusion (EB-PBF) additive manufacturing, forming unique dislocation substructures. Thus, determining the dislocation density is crucial for comprehensively understanding the strengthening mechanisms and deformation behavior. This study performed time-of-flight neutron diffraction (TOF-ND) measurements of Ti–6Al–4V alloys prepared via EB-PBF and examined the dislocation density in the as-built and post-processed states using convolutional multiple whole profile (CMWP) fitting. The present TOF-ND/CMWP approach successfully determined the bulk-averaged dislocation density (6.8 × 1013 m−2) in the as-built state for the α-matrix, suggesting a non-negligible contribution of dislocation hardening. The obtained dislocation density values were comparable to those obtained by conventional and synchrotron X-ray diffraction (XRD) measurements, confirming the reliability of the analysis, and indicating that the dislocations in the α-matrix were homogeneously distributed throughout the as-built specimen. However, the negative and positive neutron scattering lengths of Ti and Al, respectively, lowered the diffraction intensity for the Ti–6Al–4V alloys, thereby decreasing the lower limit of the measurable dislocation density and making the analysis difficult.

Evolution of dislocation structure determined by neutron diffraction line profile analysis during tensile deformation in quenched and tempered martensitic steels

The role of the dislocation structure on the work-hardening behavior during the tensile deformation of quenched and tempered martensite was studied. The evolution of the dislocation structure during tensile deformation at room temperature in ultralow-carbon 18 mass%Ni martensitic steels under the conditions of as-quenched by sub-zero-treatment (SZ) and quenched-and-tempered at 573 and 773 K (T573 and T773, respectively) was monitored using in situ time-of-flight neutron diffraction combined with the convolutional multiple whole profile (CMWP) procedure. The changes in the dislocation parameters due to tempering and deformation obtained by the CMWP procedure were explained by the metallurgical phenomena of body-centered cubic iron. The elastic limit increased in the order SZ, T573, and T773, whereas the dislocation density decreased in the opposite order, indicating that the elastic limit is not always dependent on the total dislocation density of martensite. The dislocation density in SZ, which showed a high level of work hardening after yielding, hardly changed during tensile deformation, whereas that in T573 and T773 increased with tensile straining. The dislocation arrangement parameter that represents the interaction among the dislocations was high before deformation and decreased during deformation in materials SZ and T573, whereas the parameter was maintained at a low value during the entire deformation in material T773. Large and small values of the dislocation arrangement parameter indicate weak and strong interactions, respectively. The dislocation arrangement parameter is considered helpful for estimating the increment in strength of martensitic steels by dislocation strengthening, as the coefficient α in Taylor’s equation, for both the as-quenched and tempered conditions.

Tensile Response of As-Cast CoCrFeNi and CoCrFeMnNi High-Entropy Alloys

In this research, we systematically investigated equiatomic CoCrFeNi and CoCrFeMnNi high-entropy alloys (HEAs). Both of these HEA systems are single-phase, face-centered-cubic (FCC) structures. Specifically, we examined the tensile response in as-cast quaternary CoCrFeNi and quinary CoCrFeMnNi HEAs at room temperature. Compared to CoCrFeNi HEA, the elongation of CoCrFeMnNi HEA was 14% lower, but the yield strength and ultimate tensile strength were increased by 17% and 6%, respectively. The direct real-time evolution of structural defects during uniaxial straining was acquired via in situ neutron-diffraction measurements. The dominant microstructures underlying plastic deformation mechanisms at each deformation stage in as-cast CoCrFeNi and CoCrFeMnNi HEAs were revealed using the Convolutional Multiple Whole Profile (CMWP) software for peak-profile fitting. The possible mechanisms are reported.

Effect on Microstructure and Hardness of Reinforcement in Al–Cu with Al4C3 Nanocomposites

By superposition, the individual strengthening mechanisms via hardness analyses and the particle dispersion contribution to strengthening were estimated for Al–C and Al–C–Cu composites and pure Al. An evident contribution to hardening due to the density of dislocations was observed for all samples; the presence of relatively high-density values was the result of the difference in the coefficients of thermal expansion (CTE) between the matrix and the reinforced particles when the composites were subjected to the sintering process. However, for the Al–C–Cu composites, the dispersion of the particles had an important effect on the strengthening. For the Al–C–Cu composites, the maximum increase in microhardness was ~210% compared to the pure Al sample processed under the same conditions. The crystallite size and dislocation density contribution to strengthening were calculated using the Langford–Cohen and Taylor equations from the microstructural analysis, respectively. The estimated microhardness values had a good correlation with the experimental. According to the results, the Cu content is responsible for integrating and dispersing the Al4C3 phase. The proposed mathematical equation includes the combined effect of the content of C and Cu (in weight percent). The composites were fabricated following a powder metallurgical route complemented with the mechanical alloying (MA) process. Microstructural analyses were carried out through X-ray analyses coupled with a convolutional multiple whole profile (CMWP) fitting program to determine the crystallite size and dislocation density.

Characterizing dislocation loops in irradiated polycrystalline Zr alloys by X-ray line profile analysis of powder diffraction patterns with satellites.

This work extends the convolutional multiple whole profile (CMWP) line profile analysis (LPA) procedure to determine the total dislocation density and character of irradiation-induced dislocation loops in commercial polycrystalline Zr specimens. Zr alloys are widely used in the nuclear industry as fuel cladding materials in which irradiation-induced point defects evolve into dislocation loops. LPA has long been established as a powerful tool to determine the density and nature of lattice defects in plastically deformed materials. The CMWP LPA procedure is based on the Krivoglaz-Wilkens theory in which the dislocation structure is characterized by the total dislocation density ρ and the dislocation arrangement parameter M. In commercial Zr alloys irradiation-induced dislocation loops broaden the peak profiles, mainly in the tail regions, and occasionally generate small satellites next to the Bragg peaks. In this work, two challenges in powder diffraction patterns of irradiated Zr alloys are solved: (i) determination of the M values from the long tail regions of peaks has been made unequivocal and (ii) satellites have been fitted separately, using physically well established principles, in order to exclude them from the dislocation determination process. Referring to the theory of heterogeneous dislocation distributions, determination of the total dislocation density from the main peaks free of satellites has been justified. The dislocation loop structure has been characterized by the total dislocation density of loops and the M parameter correlated to the dipole character of dislocation loops. The extended CMWP procedure is applied to determine the total dislocation density, the dipole character of dislocation loops, and the fractions of 〈a〉- and 〈c〉-type loops in proton- or neutron-irradiated polycrystalline Zr alloys used in the nuclear energy industry.

Microstructural evolution of proton irradiated Fe-2.25Cr–1Mo characterized using synchrotron XRD (SXRD)

Synchrotron X-ray diffraction data (SXRD) has been used to characterize the microstructural changes in 3.5 MeV proton irradiated 2.25Cr–1Mo (T22) steel samples as a function of dose through different techniques of X-ray diffraction line profile analysis (XRDLPA). Williamson-Hall (W–H) method, modified Rietveld method and convolutional multiple whole profile (CMWP) fitting technique have been used to evaluate the coherent domain size, r.m.s microstrain, dislocation density and dislocation character from SXRD data. It is demonstrated that XRDLPA from SXRD data is a powerful tool for extracting the microstructural parameters of irradiated samples in a reliable manner. Transmission Electron Microscopy (TEM) investigation has been carried out on unirradiated and irradiated samples to corroborate the results of XRDLPA. It is observed that dislocation density increases with dose and forms dislocation loops at highest dose. Vickers microhardness measurement has also been carried out to get the information on the mechanical property changes with dose. The variation in Vickers microhardness as a function of dose has been explained using the results from XRDLPA and TEM analysis.

Inhomogeneous Strains and Dislocation Evolution in Surface-Treated Ni-Base Superalloys

Surface treatment processes such as shot-peening create near-surface residual stresses in the component, which retard the initiation and growth of fatigue cracks. These processes, however, also induce considerable amount of strain hardening and alter the sub-surface dislocation structure of the material, which can impact its mechanical and electrochemical properties. Although these effects are critical for part performance, they have not so far been studied for surface-treated Ni-base superalloys, which are widely used for load-bearing applications. To address this, we have developed an X-ray diffraction (XRD) framework based on Convolutional Multiple Whole Profile (CMWP) fitting approach that can be used to quantify dislocation densities in shot-peened Inconel 718 components. The method exploits physics-based mechanisms for size and strain broadening to model these effects and uses dislocation contrast factors to account for deformation-induced crystallographic anisotropy in the diffraction profile. Our results suggest that shot-peening leads to one order of magnitude increase in the dislocation density of Inconel 718 alloys, which is supported by direct evidence from transmission electron micrographs. The approach developed in this work can be extended to other types of Ni-base superalloys, enabling a simple non-destructive method to calculate dislocation densities in this commercially important class of materials.

Microstructure Characterization in Individual Texture Components by X-Ray Line Profile Analysis: Principles of the X-TEX Method and Practical Application to Tensile-Deformed Textured Ti

A novel X-ray diffraction-based method and computer program X-TEX has been developed to determine the microstructure in individual texture components of polycrystalline, textured materials. Two different approaches are presented. In the first one, based on the texture of the specimen, the X-TEX software provides optimized specimen orientations for X-ray diffraction experiments in which diffraction peaks consist of intensity contributions stemming from grain populations of separate texture components in the specimen. Texture-specific diffraction patterns can be created by putting such peaks together from different measurements into an artificial pattern for each texture component. In the second one, the X-TEX software can determine the intensity contributions of different texture components to diffraction peaks measured in a particular sample orientation. According to this, peaks belonging mainly to one of the present texture components are identified and grouped into the same quasi-phase during the evaluation procedure. The X-TEX method was applied and tested on tensile-deformed, textured, commercially pure titanium samples. The patterns were evaluated by the convolutional multiple whole profile (CMWP) procedure of line profile analysis for dislocation densities, dipole character, slip systems and subgrain size for three different texture components of the Ti specimens. Significant differences were found in the microstructure evolution in the two major and the random texture components. The dislocation densities were discussed by the Taylor model of work hardening.

The Convolutional Multiple Whole Profile (CMWP) Fitting Method, a Global Optimization Procedure for Microstructure Determination

The analysis of line broadening in X-ray and neutron diffraction patterns using profile functions constructed on the basis of well-established physical principles and TEM observations of lattice defects has proven to be a powerful tool for characterizing microstructures in crystalline materials. These principles are applied in the convolutional multiple-whole-profile (CMWP) procedure to determine dislocation densities, crystallite size, stacking fault and twin boundary densities, and intergranular strains. The different lattice defect contributions to line broadening are separated by considering the hkl dependence of strain anisotropy, planar defect broadening and peak shifts, and the defect dependent profile shapes. The Levenberg–Marquardt (LM) peak fitting procedure can be used successfully to determine crystal defect types and densities as long as the diffraction patterns are relatively simple. However, in more complicated cases like hexagonal materials or multiple-phase patterns, using the LM procedure alone may cause uncertainties. Here, we extended the CMWP procedure by including a Monte Carlo statistical method where the LM and a Monte Carlo algorithm were combined in an alternating manner. The updated CMWP procedure eliminated uncertainties and provided global optimized parameters of the microstructure in good correlation with electron microscopy methods.

Evolution of microstructures, dislocation density and arrangement during deformation of low carbon lath martensitic steels

In this paper, the role of solute carbon on the strengthening and work hardening behavior of lath martensite was studied by analyzing the microstructures and dislocation density in the undeformed and deformed conditions. An increase in carbon content from 0.18% to 0.30% decreases the martensite start (Ms) temperature, leading to refinement of both the block and lath widths. Although reduction of the “effective grain size” is observed via Electron Backscatter Diffraction (EBSD) and Electron Channeling Contrast Imaging (ECCI) techniques, this effect is considered secondary in increasing the strength of lath martensite with increased carbon content. The higher strength is attributed mainly to the phase transformation-induced dislocation density in the high-carbon martensite. Comparing this total dislocation density calculated using a Convolutional Multiple Whole Profile (CMWP) fitting procedure with the estimated geometrically necessary dislocations (GND) from the misorientation distribution of EBSD analysis, it appears that a high fraction of the dislocations in lath martensitic steel is GND. Furthermore, the analysis of the samples strained to a different level suggests that the dislocation density shows minimal change during deformation, whereas the dislocation arrangement rapidly decreases at the beginning of the plastic deformation. Finally, the strain hardening behavior of the lath martensitic steel is quantitatively described by considering lath width, dislocation density, and dislocation arrangement parameters through the α coefficient in Taylor's equation.

Global optimum of microstructure parameters in the CMWP line-profile-analysis method by combining Marquardt-Levenberg and Monte-Carlo procedures

Line profile analysis of X-ray and neutron diffraction patterns is a powerful tool for determining the microstructure of crystalline materials. The Convolutional-Multiple-Whole-Profile (CMWP) procedure is based on physical profile functions for dislocations, domain size, stacking faults and twin boundaries. Order dependence, strain anisotropy, hkl dependent broadening of planar defects and peak shape are used to separate the effect of different lattice defect types. The Marquardt-Levenberg (ML) numerical optimization procedure has been used successfully to determine crystal defect types and densities. However, in more complex cases like hexagonal materials or multiple phases the ML procedure alone reveals uncertainties. In a new approach the ML and a Monte-Carlo statistical method are combined in an alternative manner. The new CMWP procedure eliminates uncertainties and provides globally optimized parameters of the microstructure.

Determination Approach of Dislocation Density and Crystallite Size Using a Convolutional Multiple Whole Profile Software

Neutron diffraction profile analysis using the whole profile fitting method is useful for obtaining microscopic information on metallic materials. To determine an appropriate fitting approach for obtaining reasonable and non-arbitrary results, we applied diffraction line profile analyses using the Convolutional Multiple Whole Profile (CMWP) method to diffraction patterns obtained using the Engineering Materials Diffractometer (TAKUMI, BL19) at the Materials and Life Science Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). The tensile specimens of 780 MPa grade bainitic steel were uniaxially stretched until the plastic strain reached a value of 0.05. We performed CMWP analyses on the obtained diffraction patterns during tensile test with various initial parameters of dislocation density and crystallite size. These parameters were optimized in the fitting procedures to minimize the weighted sums of squared residuals (WSSRs). Following this approach, we found that unsuitable initial parameter values resulted in unreasonable convergence. Therefore, initial fitting parameters should be chosen to ensure that the initial profiles are as broad as possible. Reasonable results were obtained following this suggestive approach even when the strain anisotropy parameter is set to arbitrary values.

Dislocation structure in textured zirconium tensile-deformed along rolling and transverse directions determined by X-ray diffraction line profile analysis

Specimens of cold-rolled zirconium were tensile-deformed along the rolling (RD) and the transverse (TD) directions. The stress-strain curves revealed a strong texture dependence. High resolution X-ray line profile analysis was used to determine the prevailing active slip-systems in the specimens with different textures. The reflections in the X-ray diffraction patterns were separated into two groups. One group corresponds to the major and the other group to the random texture component, respectively. The dislocation densities, the subgrain size and the prevailing active slip-systems were evaluated by using the convolutional multiple whole profile (CMWP) procedure. These microstructure parameters were evaluated separately in the two groups of reflections corresponding to the two different texture components. Significant differences were found in both, the evolution of dislocation densities and the development of the fractions of <a> and <c+a> type slip systems in the RD and TD specimens during tensile deformation. The differences between the RD and TD stress-strain curves are discussed in terms of the differences of the microstructure evolution.

Dislocation Characteristics in Lath Martensitic Steel by Neutron Diffraction

In situ neutron diffraction during tensile deformation of an as-quenched lath martensitic 22SiMn2TiB steel, was performed using a high resolution and high intensity time- of-flight neutron diffractometer. The characterizations of dislocations were analyzed using the classical Williamson-Hall (cWH) and modified Williamson-Hall (mWH) plots on the breadth method, and the convolutional multiple whole profile (CMWP) fitting method. As results, the dislocation density as high as 1015 m-2 in the as-quenched martensitic steel was determined. The dislocation density was found to decrease qualitatively with plastic deformation by the cWH and mWH plots, but hardly to change by the CMWP method. The scanning transmission electron microscopy observation supported the results of the latter method. In the CMWP method, the parameter M that represents the arrangement of dislocations was found to decrease rapidly where a very high work hardening was observed.

A multipass "low-strain-per-pass" thermomechanical processing for strengthening biomedical Co-Cr-Mo alloys

Event Abstract Back to Event A multipass "low-strain-per-pass" thermomechanical processing for strengthening biomedical Co−Cr−Mo alloys Manami Mori1, Kenta Yamanaka2, Shigeo Sato3 and Akihiko Chiba2 1 National Institute of Technology, Sendai College, Department of Materials and Environmental Engineering, Japan 2 Tohoku University, Institute for Materials Research, Japan 3 Ibaraki University, Graduate School of Science and Engineering/Institute of Applied Beam Science, Japan Introduction: Owing to their excellent wear and corrosion resistance, Co−Cr−Mo alloys have been used in various biomedical devices, such as bearings in artificial hip joints, rods for spinal-instrumentation surgery, bone plates, and screws. Further strengthening of biomedical Co−Cr−Mo alloys is desired, owing to the demand for improvements to their durability in these applications. For this purpose, we focused on dynamic recrystallization (DRX), which occurs during hot deformation at temperatures above ~1273 K, as a grain refining mechanism[1],[2]. Though the DRX-mediated grain refining process can produce exceptionally high-strength Co–Cr–Mo alloys with ultrafine-grained microstructures[3], it is still not viable in the industrial sense. In this paper, we present a concept—multipass “low-strain-per-pass” thermomechanical processing—as a method for obtaining high-strength Ni-free Co−Cr−Mo alloy. The process is carefully designed to enhance the strain accumulation for strengthening. The concept was verified by performing hot rolling of a Co−Cr−Mo alloy and the strengthening mechanisms involved were also examined. Materials and Methods: A Ni-free Co–28Cr–6Mo (mass%) alloy with 0.13 mass% nitrogen was processed by hot rolling at 1473 K with a height reduction of ~1 mm per pass. This process was repeated to realize accumulative height reduction (r) of 30%, 60% and 90%. Microstructures were investigated by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and conventional and high-resolution transmission electron microscopy (TEM and HRTEM). Mechanical properties were evaluated by room temperature tensile testing. We analyzed microstructural evolution during the hot rolling process using the convolutional multiple whole profile (CMWP) fitting for X-ray diffraction (XRD) line profiles. Results and Discussion: The EBSD analysis revealed that the grain refinement observed in this work was less significant than that in the DRX-dominated processes and the minimum grain size obtained was 37 μm for r = 90%. This indicates the “less active DRX conditions”. The strength increased monotonically with hot-rolling reduction, eventually reaching 1400 MPa in 0.2% proof stress, which is comparable to that obtained by the DRX-mediated process (Fig. 1). The XRD line-profile analysis for the hot-rolled samples revealed a drastic increase in the dislocation density with an increase in hot-rolling reduction (Fig. 2a) and proposed that the significant strengthening was primarily driven by the increased dislocation density. The CMWP analyses and complementary TEM observations also found that the amounts of stacking faults and resulting deformation twins increased with increasing hot rolling reduction (Fig. 2b). Consequently, extra strengthening, which originates from contributions of these planar defects, became apparent for greater hot-rolling reductions and contributed to the extremely high strength. Figure 1. Tensile properties of hot-rolled Co−Cr−Mo alloy prepared in this study. Figure 2. (a) Dislocation density and (b) stacking fault probability as a function of equivalent strain imposed during hot rolling. Conclusions: The obtained results demonstrated that our strategy is effective to increase the strength of Ni-free Co−Cr−Mo alloys without loss of ductility. The proposed strategy helps in reconsidering the existing strengthening strategy for the alloys, and thus, a novel feasible manufacturing route using conventional hot deformation processing is realized.

Comparison of the microstructure and the mechanical properties of AX41 magnesium alloy processed by EX-ECAP via three different routes A, Bc and C

This work is devoted to the creep-resistant AX41 magnesium alloy (Mg-4 wt.% Al-1 wt.% Ca), processed by extrusion and consecutive Equal Channel Angular Pressing (EX- ECAP) up to total of eight passes, via route A, Bc and C at 220 °C. Beyond the deformation behavior the change of the microstructures was studied by electron back-scattering and X-ray diffraction methods. Significant grain refinement was found for all processing routes (grain sizes decreased below 1 pm after 8 passes). The X-ray line profile analysis performed by Convolutional Multiple Whole Profile (CMWP) fitting method has not revealed differences between the particular dislocation structures. Route A was found to be the most effective processing route from the point of view of grain size refinement and the room temperature strength. The influence of the texture and the dislocation structure on the plastic deformation processes is discussed in detail.

Deformation analysis on F138 austenitic stainless steel: ECAE and rolling

Twinning is an alternative mechanism to achieve ultra-fine grain structures through severe plastic deformation. The properties induced in a plastically deformed material are highly dependent on the degree of deformation, accumulated deformation energy and details on grain sizes and microstructure, which are on the scale of some tens of nanometers; therefore it is very important to understand misorientation distributions and dislocation arrays developed in the samples. In this work an F138 austenitic stainless steel was solution heat treated, deformed by Equal Channel Angular Extrusion (ECAE) at room temperature up to four passes, and rolled up to 70% thickness reduction at room temperature. The microstructure evolution was analyzed by x-ray diffraction and domain sizes calculated by Convolutional Multiple Whole Profile (CMWP) model, the misorientation boundaries were measured by electron backscattered diffraction (EBSD), and transmission electron microscopy. Mechanical behavior was tested by tensile tests.