Misorientation Angle Distribution Research Articles

The microstructure and precipitated phase dependence of plastic deformation and fracture mechanism in repaired IN718 alloy by directed energy deposition

This work studied microstructural evolution, precipitate behaviors, and micro-hardness distribution along the built direction of directed energy deposited IN718 alloy. In combination with digital image correlation and crystallographic orientation analysis, the plastic deformation and fracture mechanisms of coarse columnar grains were explored in detail. The columnar grains in the deposition zone (DZ) grow along the <001> direction in the crystallography and gradually widen with increasing built height. The misorientation angle per unit length within individual columnar grains first decreases and then slows down to ∼ 0.07 °/μm when the deposition height is ∼ 1.8 mm. The micro-hardness in the DZ is gradually decreased along the built direction, which may be due to the increasing average columnar grain width and primary dendrite arm spacing, as well as reducing the volume fraction of the γ'' + γ' phases. During the uniaxial tensile loading, most plastic deformation always occurs in the DZ irrespective of the lowest hardness in the heat-affected zone (HAZ). The nucleation of microvoids is ascribed to the granular Laves phase debonding from the γ matrix. The number of microvoids gradually decreases with increasing distance from the fracture surface, which may be attributed to the strain-controlled nucleation of microvoids. EBSD results substantiated that the columnar grains near the fracture surface occur to severe lattice rotation, leading to the Kernel misorientation angle distribution in each grain interior increasing to about 1° ∼ 4°.

Patterns of Grain Fragmentation During Plastic Deformation of Metals at Small to Medium Strains (Brief Review)

Patterns of Grain Fragmentation During Plastic Deformation of Metals at Small to Medium Strains (Brief Review)

Grain boundary effects on thermal shock responses of yttria-stabilized zirconia

The rapid temperature change or thermal shock is inevitable in many engineering applications of polycrystalline yttria-stabilized zirconia (YSZ). Nevertheless, the thermal shock response of YSZ especially its dependence on the grain boundary (GB) structure in YSZ remains almost unknown to date. In this study, the effect of the GB on thermal shock behaviors of YSZ ceramics was investigated by molecular dynamics (MD) simulations in conjunction with experimental characterizations. According to the distribution of misorientation angles of GBs experimentally extracted from our sintered YSZ samples, four most common GBs with a misorientation angle ranging from 35° to 63° were constructed in MD simulations through the annealing technique. The thermal shock simulations on the bi-crystalline YSZ with such GBs show a weakening effect of the GB on the thermo-elastic strain wave, which is found to be the most significant in the [100]/[111] GB and almost vanish in its [110]/[111] counterpart. Our simulations also reveal that the weakening effect of GB on the thermo-elastic strain wave is majorly attributed to the impedance mismatch between its two adjacent grains, although the grain-boundary thermal resistance observed also can weaken the temperature wave after crossing GBs. These findings provide valuable atomic insights into the thermomechanical behaviors of YSZ under thermal shock, which will guide the design of microstructures of YSZ for some special applications in solid oxide fuel cells and thermal barrier coatings.

Hot Deformation Behavior and Mechanisms of SiC Particle Reinforced Al-Zn-Mg-Cu Alloy Matrix Composites

A systematic and comprehensive analysis of the hot deformation and mechanisms of SiC particle-reinforced aluminum matrix composites is significant for optimizing the processing of the composites and obtaining the desired components. Based on this, related research on 11 vol% SiCp particle-reinforced 7050Al matrix composites was carried out. Hot compression experiments were carried out on the Gleeble-3500 thermal simulator to study the hot deformation behavior of composites at the temperature of 370–520 °C and strain rate of 0.001–10 s−1. The hyperbolic sine constitutive equation of the material was established, and the processing map was calculated. Combining the typical metallograph and misorientation angle distribution, the microstructure evolution mechanism of composites was analyzed, and the effect of particles on recrystallization behavior was investigated. Under certain process conditions, the dominant deformation mechanism of composites changed from dynamic recovery (DRV) to dynamic recrystallization (DRX), and the grain boundary sliding mechanism began to play a role. In addition, high temperature tensile and elongation at break were tested, and it was found that the dominant form of fracture failure changed from brittle fracture of the particles to ductile fracture of the matrix as the temperature increased.

ANN-based structure peciliaties evaluation of polymer composite reinforced with unidirectional carbon fiber

At the moment, there is a growing interest in composite materials with matrices based on thermoplastic polymers; these materials are superior to traditional carbon fiber plastics due to higher fracture toughness and impact strength, low smoke generation during combustion, and high thermal and chemical resistance. The deformation behavior of such composite materials due to the high plastic deformation of the matrix differs from the behavior of traditional composites, which must be considered when performing calculations. In our study, as a model object, the features of the microstructure of single carbon thread impregnated with polysulfone were studied in order to evaluate the distribution of misorientation angles of elementary fibers, the degree of their damage, the thickness of the polymer matrix interlayers between elementary fibers in threads impregnated with more viscous thermoplastic binders. Statistical analysis of a large array of micrographs was carried out using specially developed algorithms for computer processing of electron microscopic images of a composite material. Algorithms for processing arrays of images using machine vision algorithms are proposed. Based on the analysis of the data array, the distributions of carbon fibers impregnated with polysulfone were plotted over the misorientation angle of the filaments and over the interfilament distance in the longitudinal and cross sections of the fiber. Using the machine learning method, an algorithm for detecting violations of the filament structure was implemented. The data obtained can be used to refine the calculations of the strength and deformation characteristics of composite materials with thermoplastic matrices.

The Casting and Hot Forging of Low-Carbon Copper-Bearing Steel and Its Substructural Characterization

The casting of metal alloys followed by hot forging is a widely used manufacturing technology to produce a homogeneous microstructure. The combination of mechanical and thermal energy envisages the microstructural properties of metal alloys. In the present investigation, a metal alloy of composition 0.05C-1.52Cu-1.51Mn (in weight %) was cast in an induction furnace using a zirconia crucible. The melt pool was monitored using optical emission spectroscopy (OES) to maintain the desired composition. The as-cast block was then subjected to forging under a pneumatic hammer of 0.5 t capacity so that any casting defects were eliminated. The as-cast block was reheated to a temperature of 1050 °C and held at that temperature for 6 h to homogenize, followed by hammering with a 50% strain using a pneumatic hammer. The microhardness was calculated using a Vickers microhardness testing apparatus. The microstructure characterization of the processed alloy was carried out using an optical microscope, electron backscattered diffraction (EBSD), energy-dispersive X-ray spectroscopy (EDXA), and a transmission electron microscope (TEM). The sample for optical microscopy was cut using a diamond cutter grinding machine and surface polishing was carried out using emery paper. Further, mechanical polishing was performed to prepare the samples for EBSD using a TEGRAPOL polishing machine. The EBSD apparatus was operated at a 20 kV accelerating voltage, 25 mm from the gun, and with a 60 µ aperture size. HKL Technology Channel 5 Software was used for the post-processing of EBSD maps. The procedure of standard polishing for OES and TEM sample preparation was followed. Recrystallization envisages equiaxed grain formation in hot forging; hence, the strain-free grains were observed in the strained matrix. The lower distribution of recrystallized grains indicated that the driving force for recrystallization was not abundant enough to generate a fully recrystallized microstructure. The fractional distribution of the misorientation angle between 15 and 60° confirms the formation of grain boundaries (having a misorientation angle greater than 15°) and dislocations/subgrain/substructures (having a misorientation angle less than 15°). The fraction of misorientation angle distribution was higher between the angles 0.5 and 6.5°; afterwards, it decreased for higher angles. The substructure was observed in the vicinity of grain boundaries. The softening process released certain strains, but still, the dislocation was observed to be deposited mostly in the vicinity of grain boundaries and at the grain interior. The fine precipitates of the microalloying element copper were observed in the range of size in nanometers. However, the densities of these precipitates were limited and most of these precipitates were deposited at the grain interior. The microhardness of 210.8 Hv and mean subgrain size of 1.61 µ were observed the enhanced microhardness was due to the limited recrystallized grains and accumulation of dislocations/subgrain/substructures.

Microstructure and Mechanical Properties of Dissimilar Friction-Welded Commercially Pure Ti and Ti–6Al–4V Alloy

Here, we investigated the microstructure and mechanical properties of dissimilar joints between grade 2 commercially pure titanium (CP-Ti-2) and Ti–6Al–4V alloy welded via friction welding. Accordingly, specimens with 15 mm diameter and 50 mm length were prepared, and friction welding was performed at a constant rotation speed (1600 rpm) and different upset lengths: 1, 2, and 3 mm. Electron backscattered diffraction (EBSD) method was introduced to systematically analyze grain boundary characteristic distributions (GBCDs), such as grain size, grain orientation, phase distribution, and misorientation angle distribution. In addition, mechanical properties of dissimilar joints were evaluated using the micro-Vickers hardness and tensile test machine. The microstructures at both sides of the CP-Ti-2 and Ti–6Al–4V alloy were refined materials, compared with each base material. These grain refinements were determined via dynamic recrystallization accompanied by frictional heat and severe plastic deformation. In addition, the increase in the upset length distinctively affected the change trend of the grain size of the CP-Ti-2 and Ti–6Al–4V alloy. The hardness values in regions around the weld interface were higher than those of base materials. Furthermore, yield and tensile strengths were maintained at a similar level to those of CP-Ti-2, and the tensile specimens were fractured at the base material zone of CP-Ti-2, not at the weld interface and its periphery. Consequently, friction welding to dissimilar joints between the CP-Ti-2 and Ti–6Al–4V alloy was successfully conducted and sound welded materials without welding defects were obtained.

Inference of grain boundary sliding and co-rotation of α/β phases during superplastic deformation of Zr-2.5%Nb at 700 °C through EBSD measurements

Present study explains the micromechanics of superplastic deformation of Zr-2.5 wt.%Nb alloy using EBSD analysis. The alloy when deformed in tension at 700 °C and 10−3 s−1 exhibited superplastic flow with total elongation of 650%. Different samples were deformed to intermediate strain levels for characterizing microstructure evolution and subsequently, establishing the underlying micro-mechanisms. EBSD measurements showed that local misorientations within grains did not develop during the superplastic flow. Texture weakening in α and β-Zr phases was observed and it has been shown that the resultant texture is not due to slip-based deformation. Misorientation angle distribution plots revealed a peak at 45° that corresponded to the interface angle between the Burgers OR related α and β phases. The fraction of these interfaces remained unaffected during the superplastic flow. It is concluded that the superplastic flow in Zr-2.5Nb at 700 °C is accommodated by Rachinger grain boundary sliding and co-rotation of α/β grains.

The Effect of Cooling Rate on Crystallographic Features of Phase Transformations in Zr-2.5Nb.

Zirconium (Zr) alloys are utilized as structural components for the cores of nuclear reactors due to the excellent combination of their mechanical properties and corrosion resistance under intense neutron irradiation conditions in water. The characteristics of microstructures formed during heat treatments play a crucial role in obtaining the operational performance of parts made from Zr alloys. This study investigates the morphological features of (α + β)-microstructures in the Zr-2.5Nb alloy, as well as the crystallographic relationships between α- and β-phases. These relationships are induced by the β→α(α″) displacive transformation that occurs during water quenching (WQ) and the diffusion-eutectoid transformation that takes place during furnace cooling (FC). To conduct this analysis, samples solution treated at 920 °C were examined using EBSD and TEM. The experimental distribution of α/β-misorientations for both cooling regimes deviates from the Burgers orientation relationship (BOR) at a discrete set of angles close to 0, 29, 35, and 43°. The experimental α/β-misorientation spectra are confirmed by crystallographic calculations for the β→α→β-transformation path based on the BOR. Similar spectra of misorientation angle distribution in α-phase and between α and β phases in Zr-2.5Nb after WQ and FC point to similar transformation mechanisms and the significant role of shear and shuffle in β→α-transformation.

Understanding the anisotropic tensile deformation behavior of commercially pure titanium by experiments and crystal plasticity simulations

Current work reveals the anisotropic tensile deformation mechanisms of commercially pure titanium (CP-Ti) along rolling direction (RD) and transverse direction (TD) by the statistical analysis of electron back scattered diffraction (EBSD) data and crystal plasticity (CP) simulations. The analysis of texture evolution, misorientation angle distribution, in-grain misorientation axis (IGMA) and Schmid factor indicates that the anisotropic tensile deformation behavior is originating from the anisotropic slip modes. Further CP simulation results confirm this conjecture and reveal that the higher fraction of basal slip accommodates the deformation and leads to the lower strain hardening behavior along TD. The lower uniform elongation along TD is caused by the heterogeneous strain distribution in the microstructure as deduced from digital image correlation (DIC) results and kernel average misorientation (KAM) maps.

Investigation of microstructure evolution, mechanical and corrosion properties of SAF 2507 super duplex stainless steel joints by keyhole plasma arc welding

Keyhole plasma arc welding (PAW) of the super duplex stainless steel (SDSS) is expected to achieve full-penetration joints of medium-thickness plates in a single pass with higher efficiency. However, the unique key-holing processes due to the special constricted arc behaviors cause much different thermal cycles of the liquid metals as well as changed microstructures. SDSS 2507 with a thickness of 10 mm was joined by PAW to investigate the joints' microstructure and properties. Microstructure characterization reveals substantial differences in the content of austenite, ranging from 68.9% in weld metal (WM) to 32.1% in the heat-affected zone (HAZ). The oxide inclusions in the WM enhance the hardness of the welded joints, but provide the path for crack propagation to decrease its impact toughness. While complicated microstructure is found in HAZ forming ferrite and diverse austenite, such as grain boundary austenite (GBA), intragrain austenite (IGA), and Widmanstätten austenites (WA). A small amount of secondary austenite (γ2) and chromium nitride are also found in HAZ, and they significantly deteriorate its corrosion resistance. The grain boundary misorientation angle distribution of the austenite in WM is found to be dominated by the low angle boundaries (LABs). However, its content decreases from the WM to base metal (BM). Selective corrosion occurs in all samples, where ferrite is preferentially dissolved when the extrinsic voltage is low (<0.5 V) and austenite is preferentially dissolved when the extrinsic voltage is high (>0.5 V), indicating the different electrochemical activity of the two phases.

Reconstructing orientation data from the images of IPF maps and ODF sections extracted from the literature: A data-collection method for machine learning

Crystallographic orientation data are used as a precursor to various microstructural and textural analyses as well as to perform simulations such as crystal plasticity. In the current study, a novel method is developed to reconstruct orientation data from the images of inverse pole figure (IPF) maps and sections of orientation distribution functions (ODFs) extracted from published articles. Crystallographic orientation can be expressed by Miller indices {hkl}〈uvw〉 where the {hkl} plane normal is parallel to the normal direction (ND) and the 〈uvw〉 direction is parallel to the rolling direction (RD) of the specimen. The {hkl} values of the orientations were obtained by the image processing of ND-IPF maps while the corresponding 〈uvw〉values were obtained by optimization of the ODF sections via the use of a genetic algorithm (GA). The MTEX software was used to generate ODF sections with optimized data, and these were then compared with real ODF sections to evaluate the error function of the GA. The quality of the reconstruction of orientation data was evaluated by performing the proposed method on images from the ND-IPF map and ODF sections produced through previously available experimental data. The results of both reconstructed and actual data were compared in terms of grain-size distribution, misorientation-angle distribution, texture component fractions, and the overall {hkl} and 〈uvw〉 axis distributions. Furthermore, a visco-plastic self-consistent (VPSC) simulation equipped with a Marciniak-Kuczyński (M-K) model along with visco-plastic fast Fourier transform (VPFFT) simulation was applied to reconstructed orientation data in order to obtain the plastic strain ratio (r-value), the forming limit curves (FLCs), and the strain localization distribution, respectively.

The influence of γ-fibre texture on the grain boundary character distribution of an IF-steel

The current study revealed that the development of γ-fibre texture in IF-steel through static recrystallisation alters the distribution of grain boundary misorientations and plane orientations. In the initial transformed condition, the grain boundary plane distribution has a maximum at the (110) orientation. However, as the intensity of the γ-fibre texture increased, the maximum shifted to (111) and intensified. Furthermore, the presence of γ-fibre texture gradually increased the low angle boundary population at the expense of high angle boundaries, leading to a nearly uniform misorientation angle distribution. A calculation of the disorientation distribution assuming random orientations along the γ-fibre showed a flat distribution in the domain from 0 to 60°, consistent with the observations. The presence of γ-fibre texture changed the intensity, but not the shape of the grain boundary distribution at ∑3 = 60°/[111], which displayed maxima at low energy {112} symmetric tilt boundaries.

Study of microstructure and properties of in-situ alloyed AlCoCrFeNi(Y) high-entropy alloy by laser directed energy deposition method

In this study, the equimolar AlCoCrFeNi(Y) high entropy alloy (HEA) was obtained through in-situ alloying by laser directed energy deposition (DED) method. The in-situ alloying route was designed to be economical and flexible such that a commercial cobalt-rich powder for thermal spray applications was used as the base powder, supplemented with additional elemental Al, Fe, Cr and Ni powders. For the obtained AlCoCrFeNi(Y) HEA, two phases of cubic crystal structures were identified which are Pm3¯m (221) ordered B2 and Im3¯m (229) disordered A2 BCC structures. Morphology of the resultant material was dominated by dendritic microstructure. Elongated grains with an average area of 327.1 μm2 growing in zigzag pattern along the deposition direction were observed. The average microhardness was measured to be 635.6 HV0.5. More importantly, the presence of twin boundaries was identified by the peaks in grain misorientation angle distribution at 39° and 60°. The crystallographic study also discovered fiber texture with 45° twist from <100> direction. In addition, the findings about microstructure, texture and microhardness of AlCoCrFeNi(Y) sample were compared with the results obtained by literature studies on similar HEAs, and the differences were analysed and discussed.

A Two‐Step Thermomechanical Process for Improving High‐Angle Grain Boundary Proportion and Achieving Delamination Toughening in Hot‐Rolled Steel with a Limited Slab‐to‐Plate Ratio

A Two‐Step Thermomechanical Process for Improving High‐Angle Grain Boundary Proportion and Achieving Delamination Toughening in Hot‐Rolled Steel with a Limited Slab‐to‐Plate Ratio

The influence of parent austenite characteristics on the intervariant boundary network in a lath martensitic steel

The influence of the parent austenite deformation state on the intervariant boundary network (i.e., population, plane orientation, and connectivity) of a lath martensitic microstructure was investigated using conventional EBSD mapping and five-parameter boundary analysis approach along with quantification of boundary connectivity using homology metrics. The lath martensite largely revealed a bimodal misorientation angle distribution, closely matched with the Kurdjumov–Sachs (K–S) orientation relationship. The application of deformation significantly changed the distribution, gradually reducing the intensity of the 60° misorientation angle peak. This was largely ascribed to substructure development within the parent austenite upon deformation, which stimulates particular variant/s having a habit plane (011)α′ closely parallel to the primary (111)γ and/or secondary (1overline{1 }1)γ slip plane. The interaction of these variants eventually promoted specific intervariant boundaries (e.g., 60°/[111], 10.5°/[011], and 49.5°/[110]) at the expense of 60°/[011]. The application of deformation in the parent austenite did not change the intervariant boundary plane character distribution, which mostly exhibited an anisotropic character terminated on {110} planes because of the displacive nature of the martensitic transformation. However, the extent of anisotropy progressively decreased with increasing strain in the austenite prior to transformation. The grain boundary network connectivity was markedly altered due to the local variant selection induced by the deformation. Deformation in the austenite regime generally decreased the connectivity of boundaries having a {110} plane orientation. The intervariant boundaries with the {110} twist character also displayed a similar trend, though the connectivity of {110} tilt boundaries progressively enhanced with increasing strain. The former was closely matched with a decrease in the population of 60°/[110] intervariant boundaries with the strain. The current findings suggest that the intervariant boundary network of lath martensite can be manipulated through changes in the parent austenite deformation state which, in turn, can be used to enhance key final product properties such as toughness.Graphical abstract

Mechanical properties improvement of nickel-based alloy 625 fabricated by powder-fed laser additive manufacturing based on linear beam oscillation

The action mode of laser energy affects the solidification process of the molten pool, and it determines the microstructure and mechanical properties of the deposited layers in laser additive manufacturing. In this study, a continuous laser and 50 kHz pulsed laser for the linear beam oscillation (LBO) process were proposed for the preparation of alloy 625 thin-walled structure in powder-fed laser additive manufacturing (PF-LAM). Using scanning electron microscope (SEM), energy dispersive spectrometer (EDS), electron back-scattered diffraction (EBSD), and tensile test, the samples’ microstructure, Laves phase content and morphology, grain size, misorientation angle distribution, and Schmidt factor were analyzed. The results showed that the Laves phase distribution was discrete and the content was reduced to 9.38% during the LBO process. And it produces refined, equiaxed and homogenised grains. At the same time, the LBO process promotes the transformation of the thin-walled structure of LAM from low-angle grain boundaries to high-angle grain boundaries, which helps to improve the toughness. Generally, the mechanical properties of the thin-walled structure are significantly improved by the LBO process. The strength increase in the horizontal direction of the thin-walled structure is 7.40%, which is greater than that in the vertical direction, while the elongation increase in the vertical direction of the thin-walled structure is 28.88%, which is greater than that in the horizontal direction.

Deformation mechanisms and characteristics of the meta-BIFs from an early Proterozoic shear system of the Southern Granulite Terrane (SGT), India

We studied three samples of Banded Iron Formation (BIF) rocks from Southern Granulite Terrane (SGT) of India, which was metamorphosed at high-pressure granulite facies and exhumed from 40 to 50 km depth. We examined the microstructure, texture, and deformation mechanisms of the primary minerals (quartz, magnetite, and hematite). Microstructures, variations in size and shape of quartz grains suggest that the three samples deformed to different intensities and temperatures. The EBSD derived CPOs for quartz and magnetite grains are strong, implying dislocation creep as the dominant mechanism. The presence of distinct subgrains in magnetite, rare in natural samples, attests to the same. Furthermore, twinning on {111}, as evident from the misorientation angle and axis distributions, indicates ductile deformation of magnetite below 400 °C. Subgrain boundary trace analysis in selected magnetite grains reveals that multiple-slip planes {111}, {110}, and {100} were operational. Topotaxial replacement, via redox reaction, of magnetite grains along their octahedral planes by hematite is evident. Well-developed CPOs but low (<1°) GOS values of both magnetite and hematite grains suggest that recovery processes in these were rapid. Post-replacement deformation was weak and did not affect the hematite CPOs that were inherited from the relatively more deformed host magnetite grains.

Effect of nitrogen protection on weld metal microstructure and intergranular behavior of S32101 duplex stainless steel 15 m water depth hyperbaric laser underwater welding

In this study, 16-mm-thick S32101 duplex stainless steel were welded using hyperbaric underwater laser welding system in 0.15 MPa. The misorientation angle distribution of grain boundaries in the weld metal was analyzed using the electron backscatter diffraction technique. The ionic currents near the surface of metallography were measured by the Scanning Vibrating Electrode Technique (SVET) and performed to evaluate the intergranular corrosion (IGC) resistance based on corrosion current density. The volume fractions of ferrite and austenite and the grain boundary misorientation angle affect the IGC sensitivity of the welded joints. The relationship between the grain boundary misorientation angle of the austenite and corrosion resistance was analyzed. When the weld metal was shielded with nitrogen, and the volume fraction of austenite and the frequency of Σ3 coincidence site lattice boundary in the weld was increased. The misorientation angle distribution in the austenite and the frequency of Σ3 coincidence site lattice boundary influence the IGC resistance of the welded joints.

Electron backscatter diffraction postprocessing techniques for studying recrystallisation phenomenon of Ferritic Stainless Steel

The following article looks at using scanning electron microscopy- electron back scatter diffraction techniques to study recrystallisation structures produced through hot rolling of 436 ferritic stainless steel. Characterisation of recrystallisation textures was undertaken through analysis of misorientation angle distribution diagrams, orientation distribution function maps, inverse pole figures and Taylor factor maps. These techniques were applied in a case study where typical industrial hot rolling conditions were simulated through uniaxial compression tests in a Bähr Dilatometer 850D, whereby the effect of strain rate and interpass time on recrystallisation structures was investigated.