Electron Backscatter Diffraction Method Research Articles

Effect of Warm Forging on the Microstructure and Corrosion Behavior of Austenitic Stainless Steel 316LN

The as-received as well as deformed microstructure and electrochemical corrosion behavior of warm-forged and annealed 316LN austenitic stainless steel have been investigated by using electron backscatter diffraction (EBSD) and electrochemical corrosion test methods. An attempt has been made to understand the effect of warm forging and annealing on the microstructure and electrochemical corrosion behavior of 316LN stainless steel. As-received and deformed microstructures of a sample were observed by EBSD, and from micrographs, it was observed that the refinement of grain occurs after deformation. Microstructural refinement occurs after appropriate annealing of the forged sample because of the revision of alpha ferrite and strain-induced martensite into austenite, which is formed after forging. Annealing treatment after warm forging gives better mechanical strength and optimum corrosion resistance because of the formation of homogeneous and equiaxed strain-free austenite grains. After warm forging, around 85 % of grains show a low misorientation angle of 2.5°, which shows that a lot of dislocation generation occurred during warm forging deformation and that these dislocations aligned themselves to form subgrain boundaries also known as recovery during annealing dislocation. The corrosion rate drastically increases after deformation but decreases after the annealing of deformed samples, which indicates that after appropriate annealing the corrosion resistance and repassivation capacity of materials improved because of the formation of stable oxide of chromium. The value of corrosion current density (Ecorr) shifted toward the passive direction in the Tafel plot after annealing of deformed samples, which indicates that a more protective passive film of Cr2O3 formed on the surface of the annealed sample after warm forging. The surfaces of the samples after an immersion test in the FeCl3 solution have been observed by scanning electron microscopy, and from micrographs, it has been observed that the number of pits is reduced after the annealing of a warm-deformed sample as compared with undeformed samples. The pitting potential of the samples was calculated in a simulated pressurized water reactor environment using the Tafel potentiodynamic polarization test.

Influence of Continuous Annealing Temperature on Mechanical Properties and Texture of Battery Shell Steel

To study the influences of continuous annealing temperature on microstructure, mechanical properties and textures of battery shell steel, continuous annealing experiments were conducted at 710 °C, 730 °C, 760 °C and 780 °C respectively. The mechanical properties and normal anisotropy index (r) were measured by tensile test and the textures were investigated using the method of electron backscatter diffraction (EBSD). The results show that as annealing temperature rose, the grain size, fracture elongation and r value increased, whereas the strength and yield ratio decreased. The yield strength was 122 MPa, the tensile strength was 286 MPa, meanwhile the elongation and r value arrived at 38.8% and 2.3 when the annealing temperature rose to 780 °C. After annealing, the main texture in battery shell steel is {111} <112>, followed by {111} <110>. With the increase of annealing temperature, textures in {001} crystallographic plane weakened while textures in {111} plane strengthened, which is beneficial to the deep drawability of the steel.

Martensitic Steel Microstructure Effects on Cavitation Erosion

Abstract Cavitation and cavitation erosion are sometimes unavoidable phenomena in hydro machine operation. For example, operating hydro turbines as regulating power leads to situations in which the risk of cavitation is accepted to some extent. Cavitation-resistant materials are therefore required to reduce machine damage and maintenance. This study characterizes the microstructure of two martensitic stainless steels from Francis turbines. They were already studied for cavitation erosion resistance in a previous study, and this study reveals the reasons behind the other steel having a significantly better resistance, while they had similar chemical compositions. The electron backscatter diffraction (EBSD) method is effective in defining the martensitic microstructure, specifically the block, packet, and prior austenite grain level. In addition, the retained austenite is effectively detected with the method. A fine prior austenite grain size and small packet and block sizes were found to be among the defining factors in cavitation erosion resistance of these steels. In addition, the transformation of retained austenite to martensite was detected in the edge region where cavitation had taken place. This transformation further increases cavitation erosion resistance. The better resistance of Steel 1 against cavitation was attributed to these microstructural differences. According to these findings, the microstructure in Steel 1 would be highly beneficial in building cavitation erosion resistant hydro machines and would be of interest to manufacturers of martensitic stainless steel components.

Texture Inheritance in the Ferrito-Martensite Structure of Low-Alloy Steel after Thermomechanical Controlled Processing

The electron back-scatter diffraction (EBSD) method was used to study the structural and textural states of low-carbon low-alloy steel after thermomechanical controlled processing (TMCP) and subsequent heat treatment (HT) including austenitization, holding at the temperature of the decomposition of the γ phase by the diffusion mechanism for different times, and quenching. As a result of the HT, structures were obtained consisting of polygonal ferrite and martensite in various ratios. The crystallographic textures of both martensite and ferrite after HT reproduced the texture of bainite formed as a result of the TMCP. The orientations that form this texture are related to the main orientations of deformed austenite grains upon the TMCP via the orientation relationships (ORs) intermediate between the Kurdjumov–Sachs and Nishiyama–Wassermann ORs. In the case of both ferrite and martensite, the orientational connection between the components of the texture components is explained by the onset of the realization of the phase transformation on crystallographically stipulated (including special) boundaries.

Effect of Silicon and Retained Austenite on the Liquid Metal Embrittlement Cracking Behavior of GEN3 and High-Strength Automotive Steels

GEN3 steels are a new family of automotive sheet steels developed and commercialized in the last three years, specifically for body-in-white applications. The high ductility in GEN3 steels is typically achieved through the transformation-induced plasticity (TRIP) effect by the addition of silicon or aluminum. When these steels are formed into parts, the TRIP effect of austenite to martensite transformation provides enhanced ductility. Typically, 10 to 12 micrometers of zinc coating (known as galvanized coating) is applied to automotive steel sheets for corrosion protection. Liquid metal embrittlement (LME) cracking can occur during resistance spot welding (RSW) of galvanized steels. LME cracking occurs when molten zinc penetrates prior austenite grain boundaries of the steel substrate. The precise role of silicon in the LME cracking behavior in TRIP and GEN3 steels is unknown. Therefore, a study was undertaken to examine the role of silicon in LME cracking behavior of GEN3 steels. The purpose was also to examine if the presence of retained austenite is required for LME cracking to occur. In this study, laboratory heats were prepared using three silicon levels. Samples cut from galvanized panels were welded using a resistance spot welding machine, and weld areas were examined metallographically for the presence of LME cracks. Gleeble® simulations were done to study the LME behavior of the three steels prepared. Base materials were examined with a scanning electron microscope using the electron back-scattered diffraction (EBSD) method to examine the nature of grain boundaries found. The effect of retained austenite in LME cracking was studied using the Gleeble®. Both RSW and Gleeble® results showed silicon promotes LME cracking in steels, predominantly in the weld heat-affected zones(HAZs). More low-energy, low-coincidence site lattice (CSL) boundaries were found as the silicon content of the steel was decreased. These boundaries do not host cracks. Higher silicon appeared to shrink the safe temperature range over which LME cracks could be avoided, thus indicating heat in-put control to limit cracks has limited windows as the silicon in steel goes up. It was shown that the presence of retained austenite in steel is not a prerequisite for LME cracking to occur.

Nucleation and growth analysis of [formula omitted] extension twins in AZ31 magnesium alloy during in-situ tension

The in-situ tensile test combined with electron back-scattering diffraction (EBSD) method is carried out to observe the nucleation and growth of {101‾2} extension twins in AZ31 magnesium alloy. The dynamic process of twinning can be clearly revealed by tracing the same position in the process of increasing of cumulative strain. According to the statistical analysis results, which are based on a large number of data set, Schmid Factor (SF) plays an important role in the nucleation and growth of twins. The twin variants with high SF are easier to activate and have a relatively high growth rate. However, not all the twins follow the SF rule. About 60% of the nucleated twins during the in-situ tensile test satisfy the SF rule, while for the twin growth this number is decreased to 50%. In addition, the strain accommodation factors between the deformation modes in neighboring grains and extension twins are analyzed. The shear accommodation for extension twins nucleation and growth in neighboring grains plays an important role. The shear accommodation imposed by pyramidal slip in the neighboring grains is beneficial to the twin nucleation, however, is unfavorable for the twin growing.

Elastic properties of Ti and its alloys nanostrctured due to severe plastic deformation

Studies of elastic properties of titanium and its alloys processed by severe plastic deformation are presented. The evolution of the modulus of elasticity resulting from the transformation from a coarse-grained state to an ultrafine-grained one due to severe plastic deformation (SPD) was investigated. The acoustic composite oscillator technique was used to measure the elastic modulus in a wide strain amplitude range. The microstructure was studied in detail by scanning electron microscopy and electron backscatter diffraction methods. Parameters of nanoscale porosity were measured by small-angle X-ray scattering before and after treatment with a high hydrostatic pressure (1.5 GPa). In addition, densities of titanium and its alloys in various structural states were determined by the precision method of hydrostatic weighing. As experiments showed, noticeable changes in the elastic properties resulting from the change in the grain state can be attributed to several factors, such as dislocations, nanoporosity, high internal stresses, and the structure of the materials before SPD processing.

Evaluation of diamond mosaic wafer crystallinity by electron backscatter diffraction

A mosaic substrate is a promising candidate to create large size single crystal diamonds for various types of applications. In this study, the crystal orientations of the joint areas of four single crystal plates of a mosaic substrate were measured using the high resolution electron backscatter diffraction method. The lattice rotation of [110] to [–110] (X-Y direction) was less than 0.5° and the lattice rotation mappings of [001] to [110] (Z-X direction) and [1–10] (Z-Y direction) were less than 0.2°. Considering that plate alignment is not particularly considered during the fabrication process, further improvement can be expected to realize a well- aligned mosaic substrate.

Specific Features of Microstructural Evolution During Hot Rolling of the As-Cast Magnesium-Rich Aluminum Alloys with Added Transition Metal Elements

This study addresses specific features of microstructural development during the rolling of the as-cast magnesium-rich aluminum alloys with added transition metal elements, such as Zr and Sc. For investigation purposes, three magnesium-rich aluminum alloys were chosen: 5182 without added Zr and Sc, 1565 ch with added Zr and 1570 with added Zr and Sc. Optical microscopy, X-ray texture analysis, electron microscopy, and electron backscattered diffraction methods were used in this study. This study demonstrates that two completely different patterns can be observed in the microstructure during deformation. Two zones with different subgrain sizes are formed when the alloy tends to recrystallize. Without recrystallization, the structure develops homogeneously. Recrystallization also has a significant effect on the texture formation. If recrystallization does not occur, a strong β-fiber texture is formed. However, this type of texture tends not to form during inter-deformation intervals when recrystallization occurs. Second-phase particles have the strongest effect on microstructural evolution during the hot deformation of the as-cast structure. Fine particles are capable of inhibiting recrystallization. Coarse particles initiate the PSN (particle-stimulated nucleation) mechanism and suppress the growth of the cubic texture component during recrystallization. An adequate combination of coarse and fine particles enables either better homogeneity of the structure distribution in the deformation center or better grain structure refinement.

Texture and structure formation of low-carbon low-alloy pipe steel after TMCP and heat treatment

The structure and texture of low-carbon low-alloy pipe steel after Thermo-Mechanical Controlled Processing (TMCP) and subsequent isothermal quenching were studied by the method of Electron Backscatter Diffraction (EBSD) analysis. The texture, obtained after TMCP, was formed mainly by two strong scattered orientations from {112}<110> and two weaker scattered orientations from {110}<223> and one weak orientation (001)[110]. Complex multicomponent textures were observed after heat treatment. The regions with “ferrite” and martensitic structures were identified and analyzed using Oxford Instruments HKL software. Orientations, constituting textures for both selected areas types, are associated with the basic orientations of the initial deformed austenite grains, formed during the hot deformation by orientation relationships (OR), transitory between Kurdjumov-Sachs OR and Nishiyami-Wasserman OR.

Deformation banding and static recrystallization in high-strain-rate-torsioned Al-Mg alloy

Via applying torsion tests at various strain rates, we investigate the formation of deformation bands during cold deformation and static recrystallization post the subsequent annealing of Al-Mg alloy. High-strain-rate deformations exhibit noticeable variations: high flow stress at low strains, high Schmid factor, and accelerated SRX upon subsequent annealing. We determine that the variations originate from strongly formed DBs in the high-strain-rate deformed sample. Strain analysis based on electron backscatter diffraction and convolutional multiple whole profile methods indicate that most DBs exhibit strain accumulation near their boundaries, which can accelerate SRX upon annealing. In addition, some DBs with low dislocation densities remain in the annealed workpieces. The DBs share the <111> rotation axis with the parent crystal and are generally visible in the shear-plane-normal//<111>-oriented crystal. Consequently, coincidence lattice site boundaries sharing the <111> rotation axis are observed in strain-free DBs.

The effect of reduced temperatures on microstructure development in tensile tested high-manganese steel

The current research is part of a project covering several grades of high-manganese steels (20–26 wt% Mn) with different chemical compositions, which were deformed at room and reduced temperatures. In the present paper, the microstructure development is analyzed at the onset of plastic deformation in Fe–Mn–Al–Si steel containing 21.2 wt% Mn. The examination was conducted under conditions of lowering the deformation temperature and aimed to show the influence of reduced temperatures on the occurrence of strain induced phase (martensitic) transformation.The steel samples were subjected to uniaxial deformation in a tensile test at gradually reduced temperatures, starting from 20 °C and then applying the temperatures 0 °C, −50 °C and −150 °C. The present paper includes the analysis of microstructure development and orientation relationships as well as determination of operating deformation mechanisms for samples after 10% of tensile strain. The main part of the research was carried out by means of scanning electron microscopy (SEM), using the method of electron back-scatter diffraction (EBSD).The carried out analysis indicates that within the range of small strains the mechanism controlling deformation behavior of high-manganese steel Fe–21Mn–3Al–3Si was slip of partial dislocations. This was immediately followed by the occurrence of strain induced phase transformation γ (fcc) → ε (hcp) and then locally ε (hcp) → α' (bcc). With decreasing deformation temperature a noticeable increase of the volume fraction of the martensitic phases was observed, first of all the ε-phase and to a much lesser extent α′-martensite. The ε-martensite appeared on the background of a deformed austenite initially in the form of relatively narrow bands. The α′-martensite was formed predominantly at the intersections of the ε-bands. An interesting result, however, is the fact that numerous places were also found where α′-martensite was formed in single set of parallel ε-phase bands. The preferential crystallographic orientation relations (ORs) between the γ-austenite and the strain induced ε- and α′- phases were successively followed, showing first of all the appearance of Shoji-Nishiyama (S–N) and Kurdjumov-Sachs (K–S) ORs respectively.

Crystal orientation effect on fretting fatigue induced geometrically necessary dislocation distribution in Ni-based single-crystal superalloys

The effect of crystal orientation on fretting fatigue induced crack initiation and dislocation distribution is studied by in-situ SEM observation and electron back-scattered diffraction (EBSD) in this paper. Cracks and slip lines are observed in the fretting contact area of Ni-based single-crystal (NBSX) superalloys. The in-situ SEM observation captures different crack and slip line behaviors under different crystal orientations. The EBSD analysis results show obvious misorientation and orientation deviation in the fretting contact area. For both crystal orientations, the geometrically necessary dislocation (GND) density distributions in the contact area are obtained by using Hough-based EBSD methods. The peak position of grain reference orientation deviation (GROD) and GND density matches with the fretting fatigue crack formation position. EBSD analysis shows that the dislocation density distribution on each slip system is closely related to the crack initiation direction. The direction of slip system with the maximum dislocation density agrees with the crack initiation direction obtained by in-situ observation.

Effect of unconstraint vibration treatment on fatigue damage healing for copper film

A novel approach to heal fatigue damage for copper film by unconstraint vibration was proposed in this paper. The microscope observation for copper film under various conditions was conducted on exactly the same area by electron backscatter diffraction (EBSD) method. The results found that the fraction of the low angle grain boundaries (LAGBs), the dislocation density, the stored strain energy, and the grain orientation can be restored to the original state after the unconstraint vibration treatment. The plastic strain energy generated in the damage process for the copper film before and after the treatment was analyzed. It was found that the increased plastic strain energy of the specimen after treatment is approximately equal to the consumed plastic strain energy of the specimen before treatment. The fatigue-healing experimental results showed that the fatigue crack initiation life is about 2.6 times that of no treatment.

Austenite memory during reverse transformation of steels at different heating rates

The austenite (γ) structure reversely transformed from martensite in Fe–0.55C mass% C alloy was investigated at high temperatures using in-situ an electron backscatter diffraction (EBSD) method. When the heating rate was varied, a rapidly heating produced fine γ grains, in contrast, a slow heating induced coarse γ grains having the same crystal orientations as those of the prior γ grains; known as “γ memory”. The most likely mechanism for the γ memory could be variant restrictions owing to cementite (θ). To investigate the effect of θ on the γ memory, the sample was tempered at 700 °C for 24 h and θ was precipitated. The tempered sample exhibited the γ memory irrespective of the heating rate. To clarify the origin of the γ memory, we focused on the reversely transformed γ formed adjacent to the θ and directly observed the orientation relationships (ORs) using the in-situ EBSD. A crystallographic analysis on the between neighboring ferrites (α), θ, and γ revealed the existence of Kurdjumov–Sachs OR between γ and two α (α1 and α2), Isaichev OR between α and θ, and Pitsch OR between θ and γ. In the all possible combinations, the reversely transformed γ satisfying the K–S OR for two α variants was limited to four variants. The θ variant satisfying the Isaichev OR for α1 and α2 was limited to one variant, which was close to one of the four variants by Pitsch OR, which suggests the γ memory is due to these variant restrictions among α-θ-γ.

Optimal etching sequence for austenite to ferrite ratio evaluation of two lean duplex stainless steel weldments

The color etching of LDX 2101 and LDX 2404 lean duplex stainless steel weld microstructures is optimized for an image analysis characterization process to determine the austenite-ferrite phase ratio. The results are validated in the weld metal with Feritscope® and electron backscattered diffraction methods, which are comparable to ASTM E562 manual point count results. The optimized etching and subsequent image analysis process enables an accurate measurement of the austenite-ferrite ratio in the narrow heat affected zone of these duplex stainless steel welds in addition to the fusion zone, where the application of other measurement methods is very circumstantial.

Texture development during hot deformation of Al/Mg alloy reinforced with ceramic particles

Al-3Mg alloy reinforced with B4C particles in volume fractions of 5, 10 and 15% were subjected to hot deformation to investigate the impact of presence of ceramic particles and deformation condition on final texture. Single-heat hot compression test was performed at temperatures of 300–500 °C with strain rates of 10−3 to 10 s−1. The electron backscatter diffraction method was applied to evaluate the final texture and microstructures. It was observed that the {110} fiber formed during deformation was intensified by increasing the Zenner-Holloman parameter, while deformation at lower Z makes {100} fiber pervasive throughout the matrix. Developing {100} fiber in such condition leads to continual softening of flow stress. Presence of particles by promoting particle stimulating nucleation mechanism at high Z and restricting grains rotation at low Z led to lower final texture intensity.

Exploring the mechanism of \u201cRare Earth\u201d texture evolution in a lean Mg\u2013Zn\u2013Ca alloy

The entire recrystallisation sequence and associated crystallographic texture evolution of Mg-0.8Zn-0.2Ca (wt.%) alloy was tracked using a quasi-in-situ electron backscatter diffraction (EBSD) method. Characteristic “Rare Earth” (RE) texture was formed, originating mainly from double twins and twinning-related shear bands consisting of compression and double twins. The RE textures appeared during the nucleation stage and were preserved during the relative uniform grain growth period because of solute segregation and concurrent precipitation although the alloying element content was very low. Ca and Zn co-segregated along grain boundaries with no evidence that segregation was preferred along special types of grain boundaries. The interactions between deformation microstructures, concurrent precipitation, solute drag, grain growth and texture evolution are discussed in detail. All the results indicate that Ca performs a similar role to that of RE elements in forming RE texture.

Structure and Mechanical Properties of High-Strength Austenitic-Martensitic Trip-Steel VNS9-Sh

The structure and mechanical properties of cold-rolled thin-sheet austenitic-martensitic trip-steel VNS9-Sh are studied. The method of electron back-scatter diffraction (EBSD) is used to determine the substructural state of the steel represented by mechanically hardened metastable austenite with a great number of strain twins and strain α′-martensite. The preferred places of nucleation of strain martensite in the range of intersection of strain twins and shear bands are detected. The mechanical properties of steel VNS9-Sh and the main deformation stages, i.e., microscopic yield, yield (Luders–Chernov strain) and strain hardening are determined.

New observations on built-up edge structures for improving machining performance during the cutting of superduplex stainless steel

Abstract This work features a comprehensive investigation of built-up edge (BUE) formation during machining of superduplex stainless steel (SDSS), grade UNS S32750. To visually investigate BUE formation during the machining test, a detailed examination of BUE structures obtained at different cutting speeds was performed. The BUE geometries were determined by scanning electron microscope (SEM) and 3D white light interferometry. In addition, various BUE adhesion patterns were analyzed through electron backscatter diffraction (EBSD) and nano-indentation methods. The examined BUE revealed a high level of grain refinement and elongation for both ferrite and austenite structures, as well as a tool protection effect at specific cutting speeds. Finally, the influence of BUE on the machining process in terms of chip formation and surface integrity was studied in detail. Considerable improvements could be made to the frictional conditions and workpiece surface integrity at low cutting speeds.