Reference Orientation Deviation Research Articles

Understanding the hot deformation behavior of Mo[sbnd]42Re alloy: Insights from strain rate sensitivity, microstructure, and misorientation

Mo42Re alloy, as a high-temperature structural and functional material, has broad application prospects in the nuclear industry. In this study, the hot deformation behavior of Mo42Re alloy was systematically investigated using hot compression tests and electron backscatter diffraction (EBSD) techniques in the temperature range of 1200–1500 °C and strain rate range of 0.001–1 s−1. The results showed that the flow stress of Mo42Re alloy exhibited a strong dependence on temperature and strain rate. The strain rate sensitivity index (m-value) was high under the conditions of 1350–1450 °C and 0.001 s−1. With increasing deformation temperature and decreasing strain rate, dynamic recrystallization (DRX) was significantly promoted, and the recrystallized volume fraction increased from 2.79% at 1200 °C/1 s−1 to 20.3% at 1500 °C/0.001 s−1. Meanwhile, the occurrence of and DRX effectively reduced the grain reference orientation deviation (GROD) gradients and kernel average misorientation (KAM) levels within the grains. This study revealed the mechanisms of microstructural evolution during hot deformation of Mo42Re alloy, providing important guidance for optimizing its thermomechanical processing parameters.

Mechanisms for dynamic recrystallization in a β-quenched Zr-1Nb-1Sn-0.1Fe alloy during hot compression

In this paper, uniaxial hot compression tests of β-quenched Zr-1Nb-1Sn-0.1Fe alloy under a strain of 0.91 were conducted at various temperatures ranging from 600 °C to 750 °C. The microstructure, texture evolution, deformation mode and dynamic recrystallization (DRX) mechanism were investigated using electron backscatter diffraction (EBSD). The results of the In-Grain Misorientation Axis (IGMA) method showed that the prismatic <a> was the dominant deformation mode when the temperature was 600 °C. The prismatic <a> and pyramidal <a + c> were the dominant deformation modes during hot compression between 650 and 750 °C. To study the mechanism of DRX, the geometrically necessary dislocation (GND) density, grain orientation spread (GOS) and grain reference orientation deviation (GROD) maps were calculated. The results showed that both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) coexisted during hot compression. When deformed at 600 °C, the recrystallization mechanism was mainly DDRX, while it was mainly CDRX above 600 °C. The change in the DRX mechanism can be attributed to the activation fraction of different slip systems and the resulting development of misorientation.

Origin of nucleation and growth of extension twins in grains unsuitably oriented for twinning during deformation of Mg-1%Al

A large number of anomalous extension twins, with low or even negative twinning Schmid factors, were found to nucleate and grow in a strongly textured Mg-1Al alloy during tensile deformation along the extruded direction. The deformation mechanisms responsible for this behaviour were investigated through in-situ electron back-scattered diffraction, grain reference orientation deviation, and slip trace-modified lattice rotation. It was found that anomalous extension twins nucleated mainly at the onset of plastic deformation at or near grain boundary triple junctions. They were associated with the severe strain incompatibility between neighbour grains as a result from the different <a> basal slip-induced lattice rotations. Moreover, the anomalous twins were able to grow with the applied strain due to the continuous activation of <a> basal slip in different neighbour grains, which enhanced the strain incompatibility. These results reveal the complexity of the deformation mechanisms in Mg alloys at the local level when deformed along hard orientations.

Microscopic heterogeneity of low cyclic fatigue damage in Ni-based single crystal superalloy DD413

The heterogeneous low cyclic fatigue damage level in the Ni-based single crystal superalloy DD413 was quantitatively assessed under the strain control of ±0.8% and ± 1.1%. The specimens subjected to ±0.8% strain amplitude exhibited an almost pure elastic deformation response throughout the entire cyclic loading period. In contrast, the ±1.1% strain-controlled deformed specimen exhibited a gradual increase in plastic strain, rising from 0.046% in the 1st cycle to 0.072% by the 268th cycle. The brittle carbides caused a significant mechanical incompatibility with the matrix. This was observed through the orientation dispersal over 16° in the {001} pole figure of the ±1.1% specimen, which was substantially broader than the ±0.8% specimen where the dispersion was only 1.2°. The large orientation gradient in the interdendrite (IR) triggered the dispersion of the microstructure-averaged orientation of the ±1.1% specimen, as evidenced by a mean grain reference orientation deviation (GROD) angle three times higher in the IR compared to the dendrite (DR). While the DR and IR of ±0.8% specimen showed similar mean GROD angles. This substantial orientation gradient was sustained by the high density of geometrically necessary dislocations (GNDs) in the IR, which was double that of the DR. Differently, the DR and IR in the ±0.8% specimen exhibited similar mean densities of GNDs. The study suggests that minimizing microstructural heterogeneity at the dendritic scale may enhance the durability of DD413 alloy components when exposed to cyclical stress with greater strain amplitudes.

Quantitative analysis of partially recrystallised microstructures from BSE-SEM imaging

A method is proposed for the determination of microstructural information, such as grain size and recrystallised fraction, directly from the BSE images. The approach exploits the channelling contrast present in the BSE images to extract maps analogous to grain reference orientation deviation (GROD) and kernel average misorientation (KAM) without the need for orientation information. These maps are then processed in order to determine the recrystallised fraction in an efficient manner. The BSE image series are acquired using the eCHORD acquisition setup: the sample is first tilted and a series of 30 images are acquired as the sample rotates. Compared to results obtained from orientation data, this method significantly reduces the acquisition and data processing time.

Analysis of the high cracking resistance of a Co Ni superalloy during laser additive manufacturing

A newly developed CoNi-based superalloy is demonstrated to be tolerant of a wide range of laser powder bed fusion print conditions, with limited defect content and high relative densities. These promising traits motivated investigation of the structural uniformity in samples printed at the upper end of the scan velocity processing window (>▪). A new misorientation metric, starting reference orientation deviation (SROD), was calculated from ▪-scale 3D microstructure information to examine structure evolution during epitaxial growth of columnar grains. Misorientations of >20° were observed within the large columnar grains that grew through multiple build layers. The SROD observations highlight the CoNi superalloy's ability to plastically deform to high levels, as evidenced by misorientation gradients, across the range of temperatures experienced in laser additive manufacturing. Misorientation gradients within the columnar grain structure are high relative to Ni base superalloys, allowing for strengthening with high volume fractions of L12 precipitates.

Effects of grain structures on fatigue crack propagation behavior of an Al-Cu-Li alloy

The effects of two different grain structures on fatigue crack propagation (FCP) behavior of an Al-Cu-Li alloy were investigated. The results indicate that the fibrous grained and equiaxed grained samples exhibit significantly different FCP resistances. The FCP rates are particularly different at the Paris stage at the stress intensity factor range (ΔK) is about 20 MPa∙m1/2, the equiaxed grained sample is 8.23 × 10-4 mm/cycle, while the fibrous grained sample is up to 1.65 × 10-3 mm/cycle. The results of electron backscattered diffraction (EBSD) analysis of the crack propagation paths show that about 58.7 % of crack paths are transgranular and 67.6 % of the cracks are deflected in the fibrous grained sample, most crack segments are parallel to {111} 〈101〉 slip system. While in the equiaxed grained sample, the probabilities of transgranular and intergranular propagation are both about 50 % and 73.2 % of the cracks are deflected, most crack segments are parallel to {111} 〈011〉 slip system. The grain reference orientation deviation (GROD) and the kernel average misorientation (KAM) maps show that the degree of deformation at the grain boundaries of the fibrous grained sample is higher than the equiaxed one.

Optimized method for the identification of slip directions in Mg alloy based on intragranular misorientation axes analysis

In this work, an optimized method was proposed to identify the activated slip directions (i.e., gliding direction of dislocations) based on intragranular misorientation axes (IGMA) analysis only using electron backscattered diffraction (EBSD) data. By using MTEX toolbox in MATLAB software, the figures which showed the slip directions and the change of rotation angles (i.e, the grain reference orientation deviation (GROD) angles) in each grain, were plotted based on the EBSD data. By comparing the directions in which the GROD angle increases with the slip directions in the grain, the potential activated prismatic slip directions can be determined. Taking two grains in the extruded Mg–6Zn–1Y-0.5Zr alloy as examples. Two different prismatic slip directions belonging to two prismatic slip systems, [1-210] (GROD value: 0.64 → 0.75) and [-12-10] (GROD value: 0.34 → 0.74), were activated in the grain 1. Meanwhile, only one prismatic slip system, (10-10) [-12-10] (GROD value: 0.29 → 0.8), was initiated in the grain 2. Moreover, this method was further applied to determine the basal slip systems. Two basal slip systems, (0001) [-12-10] (GROD value: 2.7 → 4) and (0001) [-2110] (GROD value: 3.2 → 4.2), were activated in the selected grains, demonstrating that this method is also suitable for identifying the basal slip systems except for the prismatic systems. In summary, a novel method to determine the active slip directions in Mg alloys was successfully developed and experimentally validated in Mg alloys, which was simpler and more efficient compared to other widely utilized methods.

Assessment of activation volume in 304L SS at high temperatures

The variation in apparent and true activation volumes of 304L SS with true plastic strain has been evaluated at three temperatures (973 K, 1073 K and 1123 K) over the strain rates of 3 × 10−3 s−1, 3 × 10−4 s−1 and 3 × 10−5 s−1. The instantaneous strain rate sensitivity parameter was derived from strain-rate jump tests across different strain levels to estimate apparent activation volume. The values of apparent activation volume were higher at 973 K than at other temperatures. In contrast to the apparent activation volume, the estimated values of true activation volume using internal-stress-based kinetic rate law systematically increase with the increasing temperature from 973 K to 1123 K. The higher flow stress with a larger strain hardening rate at 973 K leads to a lower true activation volume in the steel compared to other temperatures. The model outcomes revealed that the instantaneous strain rate jump-up or jump-down leads to the change in the internal and effective stresses. The observed variations in geometrically necessary dislocation density (GND) and intra-grain reference orientation deviation (GROD) in the substructure substantiated the predicted variation in the internal stress level upon strain rate jump up/down. The true activation volume was estimated for a fixed value of mobile dislocation density (ρm = 5 × 1011 m−2) and for varying mobile dislocation density. Irrespective of ρm values, the estimated true activation volume values for 304L SS were in the order of 102 b3 to 103 b3, thereby implying that the intersection of dislocations coupled with the climb of jogged dislocations is the dominant mechanism during tensile deformation at high temperatures. Based on the analysis using the kinetic rate law with a fixed value of mobile dislocation density, it has been realized that the multiplication of effective stress and true activation volume remains constant across the plastic strain levels for the given combination of strain rate and temperature.

Plastic Damage Assessment in 316 Austenitic Steel Using the Misorientation Parameters from an In Situ EBSD Technique

Plastic damage assessment in 316 austenitic steel was performed in this research by using the misorientation parameters derived from an in situ EBSD technique. With the increase in plastic strain, the misorientation parameters, such as the Grain Reference Orientation Deviation (GROD), Grain Orientation Spread (GOS), the Grain Orientation Spread over the grain Diameter (GOS/D), and Geometrically Necessary Dislocation (GND) density presented a growing trend. Nevertheless, the variation in GROD did not show a monotony trend, and the relative increase in the amplitude of GOS and GND density was less in the late plastic stage. Compared with the above parameters, the (GOS)/D exhibited a near-linear increase during the plastic tensile stage. As the specimen was stretched to a strain of 56.99%, the (GOS)/D increased 8.9 times compared with the original specimen. The results showed that the (GOS)/D parameter has the potential of becoming an indicator for the assessment of plastic damage in 316 steel.

On the plasticity of a hot-rolled Zircolay-4 via a combination of in-situ acoustic emission and ex-situ EBSD techniques

The plastic anisotropy of a hot-rolled Zircaloy-4 (Zr-1.56Sn-0.22Fe-0.11Cr) occurring during compressive loading in three orthogonal directions was analysed using the acoustic emission (AE) technique and scanning electron microscopy (SEM). In particular, AE was used for in-situ monitoring of the activity of individual deformation mechanisms. The microstructure was characterized by the electron backscatter diffraction (EBSD) technique in the initial state and after deformation of 2% and 12%, respectively. The grain reference orientation deviation (GROD) maps estimated from the EBSD data reveal the evolution of slip system activities in individual grains. During compressive loading along the rolling and transverse directions (RD and TD, respectively), dislocation glide and twinning are dominant deformation mechanisms. Moreover, the AE technique in combination with EBSD analysis indicates that more intensive twinning in RD, reflected by a high twin volume fraction, is rather given by twin thickening than massive twin nucleation. With respect to the initial texture, the twinning is almost suppressed during loading along the normal direction (ND) and plastic deformation is realized by several slip systems, including multiple slip.

The Synergistic Effects among Crystal Orientations, Creep Parameters, Local Strain, Macro–Microdeformation, and Polycrystals’ Hardness of Boron Alloyed P91 Steels

This article induces proficient microstructure––creep reciprocity by electron backscatter diffraction (EBSD) and impression creep measurements (ICM). The article has further contributed to understanding the synergistic effects of boron in extenuating microstructural degradation. Herein, 22 and 100 ppm boron alloyed P91 steels (P91 and P91B steels, respectively) are subjected to ICM, assessing stress exponent (n), threshold stress (σTh), effective activation volume (Veff), and activation energy. Base metal and narrowed crept realm of each steel are measured by employing EBSD. ICM results are correlated with crystal orientations and 1) strain accumulation, 2) macroscopic and 3) microscopic deformation resistance, and 4) hardness of grain in polycrystals by calculating kernel average misorientation (KAM), elastic stiffness, grain reference orientation deviation (GROD), and Taylor factor (M) within microstructure before and after ICM. Measurements of P91B steel show a small value of n and Veff and a high value of σTh and activation energy as regards P91 steel. Lower KAM and stiffness before and after creep, higher GROD in base metal, and lower GROD in the crept realm in P91B steel as regards P91 steel corroborate microstructural homogeneity. M indicates both steels are hard before creep, while ICM moderates hardness. Finally, this study reveals synergistic effects of crystal orientations, KAM, stiffness, GROD, M, and creep.

Laser Powder Bed Fusion Additive Manufacturing of Fe3Al-1.5Ta Iron Aluminide with Strengthening Laves Phase

Advanced aluminides strengthened with incoherent Laves phase precipitates are promising lightweight and creep-resistant alternatives for high-alloy steels and superalloys for high-temperature critical components up to 750 °C service temperature. A significant issue with manufacturing these aluminides with conventional casting is the strong coarsening tendency of the Laves phase precipitates at elevated temperatures, leading to a significant strength reduction. In this context, the short lifetime of the melt pool in additive manufacturing and its fast solidification and cooling rates promise to consolidate these aluminides with homogeneously distributed fine Laves phase particles without coarsening. The main scientific objective of this work is to exploit the unique characteristics of the laser powder bed fusion (L-PBF) additive manufacturing (AM) process to print dense and crack-free bulk Fe3Al-1.5Ta samples containing uniformly distributed (Fe, Al)2Ta Laves phase precipitates. The Fe-25Al-2Ta (at.%) alloy was selected for this work since its creep resistance at 650 °C surpasses the one of the P92 martensitic–ferritic steel (one of the most creep-resistant alloys developed for steam turbine applications). Fundamentals on process–microstructure relationships governing the L-PBF-fabricated builds are provided by a detailed microstructural characterization using X-ray diffractometer (XRD) and ultra-high-resolution scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX) and high-resolution electron backscatter diffraction (EBSD) detectors. Orientation imaging microscopy (OIM) and grain reference orientation deviation (GROD) maps were applied to measure texture and visualize substructures within the grains. The mechanism of voids formation, morphology, and volume fraction as a function of the input energy density was identified. The melting and solidification dynamics led to microstructures with large columnar grains, porosity, and periodic cracks during the printing process. Processing samples at the building temperatures below the brittle-to-ductile transition temperature, BDTT (750 °C), often caused severe macrocracking and delamination. Crack-free samples with densities higher than 99%, some approaching 99.5%, were fabricated from pre-alloyed gas-atomized powders with a combination of high laser power (250–300 W), slow-to-medium scanning speed (500–1000 mm/s), and 800 °C build plate preheating using a 67° rotation scanning strategy. The morphology of the pores in the volume of the samples indicated a relatively sharp transition from spherical geometry for scanning speeds up to 1000 mm/s to crack-like pores for higher values. The ultra-fast cooling during the L-PBF process suppressed D03 Fe3Al-ordering. The Fe3Al-1.5Ta builds were characterized by B2 FeAl-type order clusters dispersed within a disordered A2 α-(Fe, Al) matrix. Additionally, the (Fe, Al)2Ta Laves phase (C14–P63/mmc) was predominantly formed at the matrix phase grain boundaries and frequently dispersed within the grains. The quantitative EDX analysis of the matrix gave 77.6–77.9 at.% Fe, 21.4–21.7 at.% Al, and 0.6–0.8 at.% Ta, while the composition of the Laves phase was 66.3–67.8 at.% Fe, 8.7–9.8 at.% Al, and 22.4–24.9 at.% Ta, indicating that the Laves phase is considerably enriched in Ta with respect to the matrix. The L-PBF-fabricated alloys were characterized by coarse, columnar grains which grow epitaxially from the substrate, were several m in width, and extended across several layers along the building direction. The grains exhibited a relatively strong microtexture close to &lt;0 0 1&gt; with respect to the building direction. The L-PBF builds showed a bulk hardness value comparable to the as-cast and spark plasma-sintered counterparts. A negligible variation of the hardness across the build height was observed. Within the framework of this study, we demonstrated that the porosity and cracking issues could be resolved mainly by controlling the process parameters and preheating the build platform above the BDTT. Nevertheless, alloy modifications and/or post-manufacturing processing are required for microstructure refinement.

Orientation-Dependent Indentation Behaviour of Additively Manufactured FeCo Sample: A Quasi In-Situ Study

The quasi in-situ indentation behaviour of &lt;110&gt;||BD and &lt;111&gt;||BD-oriented grains in a FeCo alloy is studied in this investigation. The effect of build height on melt pool shape and melt pool size is also studied by finite element method simulations. As the building height increases, the aspect ratio of the elliptical melt pool increases. Correspondingly, the effect of the laser scan speed on the melt pool shape and size is studied by the finite element method, because, as the laser scan speed increases, the aspect ratio of the elliptical melt pool increases, too. The microstructural characterisation of the indentation area before and after indentation is performed by electron backscatter diffraction (EBSD). Based on the EBSD data grain reference orientation deviation (GROD), calculations are performed to describe the effect of indentations on the neighbouring grain orientations. High GROD angles are detected in the neighbouring grain region adjoining the indented grain. An in-depth slip trace analysis shows the activation of all three slip systems ({110}&lt;111&gt;, {112}&lt;111&gt; and {123}&lt;111&gt;) which is also confirmed by slip lines on the sample surface that are detected by laser scanning confocal microscopy. A high concentration of geometrically necessary dislocations (GNDs) are observed on the adjoining area to the indentation. Local surface topography measurements by laser scanning confocal microscopy confirmed the formation of pile-ups near the indentation.

Electroplastic Effects on the Mechanical Responses and Deformation Mechanisms of AZ31 Mg Foils.

Electrical-assisted (EA) forming technology is a promising technology to improve the formability of hard-deformable materials, such as Mg alloys. Herein, EA micro tensile tests and various microstructure characterizations were conducted to study the electroplastic effect (EPE) and size effect on the mechanical responses, deformation mechanisms, and fracture characteristics of AZ31 Mg foils. With the assistance of electric currents, the ductility of the foils was significantly improved, the size effects caused by grain size and sample thickness were weakened, and the sigmoidal shape of the flow stress curves during the early deformation stage became less obvious. The EBSD characterization results showed that the shape change of the flow stress curves was due to the EPE suppressing the activation of extension twinning at the early deformation stage, especially for the coarse grain samples. The suppression of extension twinning resulted in a quick increase in flow stress due to the dislocation-dominant work hardening, and the increased flow stress eventually promoted extensive deformation twins at large deformation. Thus, as the sample strained to 10% tensile deformation, the EA-tested samples showed a larger volume fraction of deformation twins than the non-EA samples. The reference orientation deviation analysis verified that the deformation twins in the EA samples were formed in the large deformation stage. Combined with the fractography, the EPE also improved the ductility by suppressing the expansion of cleavage surfaces.

Effect of loading path on grain misorientation and geometrically necessary dislocation density in polycrystalline aluminum under reciprocating shear

Solid phase processing (SPP) is a promising alloy fabrication technique to produce fine and homogeneous grain structures for high-performance alloys. However, there is very limited modeling capability to understand and predict the grain refinement during SPP. In this work, the crystal plasticity theory was used to study elastic–plastic deformation in polycrystalline aluminums under large shear deformation. Two approaches, kernel averaged misorientation (KAM) and grain reference orientation deviation (GROD), were used to assess the grain misorientations. The geometrically necessary dislocation (GND) density was computed with the plastic strain rate. The deformation simulations were carried out under two loading conditions to investigate the effect of loading paths on the evolutions of grain misorientation and GND density. The results show that the regions with high misorientation and GND density first appear near grain boundaries. These regions then extend toward interior grains. The loading path affects plastic deformation accumulation and recovery, hence dislocation evolution and misorientation. Both two- and three-dimensional simulations showed that the spatial and temporal evolutions of GROD, KAM, and GND density are closely correlated, which indicates they all can be used as criteria of grain refinement or recrystallization, the essential information for grain refinement simulations.

Load dependent microstructural evolution in an as-cast 26% Cr high chromium cast iron during unlubricated sliding

In the current study, an as-cast 26% Cr high chromium cast iron (HCCI) alloy was subjected to dry-sliding linear wear tests, under different loads. The loads were selected based on analytically computing the critical load (PC) i.e., the load necessary to induce plastic deformation. The PC was calculated to be 15 N and accordingly, a sub-critical load (5 N) and an over-critical load (20 N) were chosen. The influence of increasing the load during the wear test was investigated in terms of the matrix microstructural behaviour and its ability to support the surrounding carbides. The morphological aspects of the wear tracks, and the deformed matrix microstructure adjacent and underneath the track was analysed by confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM), respectively. No evidence of plastic deformation of the matrix was observed below PC. On the contrary, at loads equal to and higher than PC, the austenitic matrix plastically deformed as evidenced by the presence of slip bands. Electron backscattered diffraction (EBSD) measurements in terms of grain reference orientation deviation, and micro-Vickers hardness of the austenitic matrix indicated a deformation depth of about 40 µm at the maximum applied load of 20 N. The active wear mechanisms during sliding were a combination of both adhesive and abrasive wear, although increasing the load shifted the dominant mechanism towards abrasion. This was primarily attributable to the increased propensity for carbide cracking and fracturing, combined with the inability of the hardened austenitic matrix surface and sub-surface to adequately support the broken carbide fragments. Moreover, the shift in the dominant wear mechanism was also reflected in the wear volume and subsequently, the wear rate.

Low Cycle Fatigue Characteristics of Oxygen-Free Copper for Electric Power Equipment

The effect of heat treatment on tensile and low cycle fatigue properties of the oxygen-free copper for electric power equipment was investigated. The heat treatment at 850 °C for 20 min, which corresponds to the vacuum brazing process, caused the grain growth and relaxation of strain by recrystallization, and thus, the residual stress in the oxygen-free copper was reduced. The tensile strength and 0.2% proof stress were decreased, and elongation was increased by the heat treatment accompanying recrystallization. The plastic strain in the heat-treated specimen was increased compared with that in the untreated specimen under the same stress amplitude condition, and thus, the low cycle fatigue life of the oxygen-free copper was degraded by the heat treatment. Striation was observed in the crack initiation area of the fractured surface in the case of the stress amplitude less than 100 MPa regardless of the presence of the heat treatment. With an increase in the stress amplitude, the river pattern and the quasicleavage fracture were mainly observed in the fracture surfaces of the untreated specimens, and they were observed with striations in the fracture surfaces of the heat-treated ones. The result of the electron backscattered diffraction (EBSD) analysis showed that the grain reference orientation deviation (GROD) map was confirmed to be effective to investigate the fatigue damage degree in the grain by low cycle fatigue. In addition, the EBSD analysis revealed that the grains were deformed, and the GROD value reached approximately 28° in the fractured areas of heat-treated specimens after the low cycle fatigue test.

Microstructure Evolution during Hot Deformation of UNS S32750 Super-Duplex Stainless Steel Alloy.

The present paper analyzes UNS S32750 Super-Duplex Stainless Steel hot deformation behavior during processing by upsetting. The objective of this paper is to determine the optimum range of deformation temperatures, considering that both austenite and ferrite have different deformation behaviors due to their different morphology, physical, and mechanical properties. Because the capability of plastic deformation accommodation of ferrite is reduced when compared to austenite, side cracks and fissures can form during the hot deformation process. Consequently, it is important to find the optimum conditions of deformation of this type of stainless steel to establish the best processing parameters without deteriorating the material. The experimental program involved the application of hot deformation by the upsetting method on a series of samples between 1000 °C and 1275 °C, with a total degree of deformation of 30%. The resultant samples were examined by SEM-EBSD to establish and analyze the evolution of the phases present in the structure from several points of view: nature, distribution, morphology (size and shape), and their structural homogeneity. The GROD (Grain Reference Orientation Deviation) distribution map was also determined while taking into account the possible precipitation of the secondary austenite phase (γ2-phase) and the analysis of the dynamic recrystallization process according to the applied deformation temperature. The main conclusion was that UNS S32750 SDSS steel can be safely deformed by upsetting between 1050–1275 °C, with an experimented total degree of deformation of 30%.

Experimental mesoscopic investigation of the local cyclic plasticity of a non-oriented electrical steel

Complementary mesoscopic investigations have been carried out on a notched specimen, made of Fe–3%Si steel and submitted to fatigue loading. Load control fatigue testing was conducted to ensure localised cyclic deformation and the resulting displacement fields were measured by means of Digital Image Correlation (DIC). Electron Channelling Contrast Imaging (ECCI) and Electron Back-Scatter Diffraction (EBSD) complete the DIC data by giving a different view of the local plasticity, as they image the dislocation structure and map their related characteristics, such as misorientation.Hence, two misorientation based criteria, namely Grain Reference Orientation Deviation (GROD) and Grain Orientation Spread (GOS) were considered for EBSD analysis. Based on a previous study, a <GOS> − Δεt abacus has been coupled with a <GOS> − DIC abacus in order to evaluate locally the encountered strain field and link this latter to an equivalent total strain variation. The obtained results have been discussed from the evolution of the dislocations structures, as observed by ECCI.This combination of mesoscopic techniques clearly emphasizes the local deformation by means of both qualitative and quantitative measurements. On one hand, DIC and EBSD measurements indicate the presence of strain localisation which can be correlated to a certain level of cyclic strain amplitude. On the other hand, the variation of the strain levels and its distribution when moving away from the notch are confirmed by the dislocation structures evolution seen by ECCI. Such structures vary from cells, vein and channels and entangled dislocations regions as the analysed areas go away from the notch. At a local scale, the DIC measurements behave as numerous virtual extensometers while its combination with EBSD and ECCI data confirms the correlation with the accumulated cyclic strain.