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The grain boundary strengthening effect (GBSE) was investigated for nickel-based superalloy bicrystals with various misorientations under different temperatures and loading directions. The results show that the GBSE is enhanced with the increase of misorientation and insensitive to the temperature. Besides, the loading direction relative to GB also has strong effect on GBSE. On the other hand, the GBSE is often accompanied by GB cracking. The trend of GB cracking is heightened with the increase of misorientation and temperature. However, the trend of GB cracking is reduced strongly when the loading direction transforms from parallel direction to vertical direction.

Wide opportunities of using fine-grained materials as structural and functional materials with advanced physical and mechanical properties have proved the importance of improving the existing technology and creating new processing methods and treatment conditions for such ma-terials. At the same time, a preliminary theoretical analysis using mathematical models gives an opportunity to significantly reduce the cost of such experimental studies. Thus, it is necessary to develop multilevel models of polycrystalline metals and alloys based on crystal plasticity with the description of structure, deformation mechanisms and refinement at various scale levels. To con-struct a correct model of such a class, it is necessary to analyze information and arrange a large amount of experimental data about grain structure refinement. The article presents a review of the experimental studies describing and analyzing the grain structure refinement during severe plastic deformations of various metal alloys. The refine-ment mainly occurs at low temperatures that are a priori lower than the temperatures at which re-crystallization becomes an important factor and the solid-state phase transitions may take place. We have summarized the significant physical mechanisms of the grain refinement during cold deformation based on the arranged experimental data from the review. All the considered articles pay attention to the local accumulation of lattice dislocations inside the grains (in the form of flat clusters), which leads to the lattice curvature and separation of grains into cells. As a result of a further accumulation of dislocations in the walls, there comes an increase in misorientation of the neighboring cells. The curved lattice is unstable (it seems clear that the flat clusters become a source of such curvatures) and relaxes with the formation and movement of the partial disclina-tions, which leads to the rotation of the adjacent grain regions and creation of new grain bounda-ries. In addition, the mesoscale defects located at the junctions of the grains (including the boundary intersection disclinations), flat clusters of the dislocations of the orientational mismatch at the grain boundaries and partial dislocations in the grains have a significant effect on the frag-mentation. The articles about the severe plastic deformation at high temperatures are briefly de-scribed here. It is noted that recrystallization is the main mechanism of the fine-grained structure formation under these conditions. We suggest including the description of the discussed mechanisms in the multilevel con-stitutive material models. When new experimental data appear for a specific process of the severe plastic deformation, the considered refinement mechanisms can be added.

Grain boundary structures have long been known to depend on factors such as solutes and temperature. In this work, in-situ atomic scale imaging was used to observe the faceting of a Σ21a [1 1 1]-tilt-axis boundary at 600 ∘C and 800 ∘C in a Pt-5Au (at. %) nanocrystalline alloy. With an increase in temperature, we observe an evolution from many, shorter facets to fewer, longer facets. The preferred facets are shown to be symmetrically equivalent tilt boundaries, via the fundamental zone formalism. Simulation of Pt bicrystals reveals that these preferred facets do not lie in an energy minimum (of the tilt boundaries that the grain boundary misorientation could access); however, calculation of the segregation enthalpy of Au to these grain boundary lattice sites indicates a greater preference of Au, reducing the grain boundary energy, and explaining the facet stabilization observed.

Chemical vapor deposition has been highlighted as a promising tool for facile graphene growth in a large area. However, grain boundaries impose detrimental effects on the mechanical strength or electrical mobility of graphene. Here, we demonstrate that high-pressure hydrogen treatment in the preannealing step plays a key role in fast and large grain growth and leads to the successful synthesis of large grain graphene in 10 s. Large single grains with a maximum size of ∼160 μm grow by recrystallization of nanograins, but ∼1% areal coverage of nanograins remains with 28-30° misorientation angles. Our findings will provide insights into mass production of high-quality graphene.

The computer simulation methods have been applied to calculate structure and energy of symmetric tilt grain boundaries with the misorientation axis [100]. The calculations have been carried out with the use of the structural-vacancy model previously developed by the authors. The misorientation angles of grain boundaries of common type have varied from 0° up to 90° while the increment has amounted 1°. The the reciprocal density of the coincidence sites in special grain boundaries has amounted Σ ≤ 53. The calculations have been carried out with the use of the Morse pair potential and the Cleri–Rosato many-body potential. It is shown that the dependence of the energy of grain boundaries on the misorientation angle when calculated with different potentials has a similar form, and their structure does not depend on the choice of potential and is in good agreement with high-resolution electron microscopic images. Only one special grain boundary is distinguished on the energy curve which is Σ5(013). It has been found that the structure grain boundaries may be represented by a limited number of atomic groups that have been named basic structural units. The structure of low-angle grain boundaries with the misorientation angle less than 8° is described by alternation of basic structural units of D types and ideal crystal, while the structure of low-angle grain boundaries with the misorientation angle ranging from 8° up to 13° is described by alternation of structural units of C and D types, from 14° up to 23° – B and C types. High-angle grain boundaries in the range of misorientation angles from 24° up to 37° contain only of basic structural units of B types, from 38° to 50° – A and B, more than 50° – only A.

International audience; We document how dynamic recrystallization by subgrain rotation (SGR) develops in natural olivine-rich rocks deformed in extension to up to 50% bulk finite strain (1473 K, confining pressure of 300 MPa, and stresses between 115 and 180 MPa) using electron backscatter diffraction (EBSD) mapping. SGR occurs preferentially in highly deformed grains (well-oriented to deform by dislocation glide) subjected to local stress concentrations due to interactions with hard neighboring grains (poorly-oriented olivine crystals or pyroxenes). Subgrains (misorientation

Sanicro 25 is a candidate material for reheaters and superheaters used in 650–700 °C advanced ultra-supercritical power plants. A composition-matched weld filler metal has been developed to join Sanicro 25 tubes through tungsten inert gas welding. Creep tests of the Sanicro 25 welded joint were conducted at 973 K under a stress of 180–240 MPa. The creep lifetime decreased with an increase in applied stress. The welded joint crept at 180 MPa fracture at the base metal (BM) in a mixed fracture type, and voids were the main damage form in the BM, which had low ductility in the welded joint. Creep fractures occurred in the weld metal (WM) in an intergranular manner at 200–240 MPa, with wedge cracks representing the main damage form and a lower creep ductility in WM. The distribution and strengthening mechanism of the nano-MX and nano-Cu phases in the WM of joint were close to those of pure BM after creep. The growth of carbides in the WM was restrained by element B during the 180 MPa creep test, which caused increasingly serious carbide coarsening in the BM. The amount of low misorientation angle boundaries in the WM following the creep substantially increased. Besides, the creep deformation of the welded joint at 180 MPa is dominated by BM, and the change in the weld grain shape is small. For tests under 200–240 MPa, the creep deformation of the welded joint was dominated by the weld, and the shape of the weld grain changed significantly.

The effect of grain boundary (GB) defects on the tribological properties of MoS2 has been investigated by molecular dynamics (MD) simulations. The GB defects-containing MoS2 during scratching process shows a lower critical breaking load than that of indentation process, owing to the combined effect of pushing and interlocking actions between the tip and MoS2 atoms. The wear resistance of MoS2 with GB defects is relevant to the misorientation angle due to the accumulation of long Mo-S bonds around the GBs. Weakening the adhesion strength between the MoS2 and substrate is an efficient way to improve the wear resistance of MoS2 with low-angle GBs.

Superalloy inspired Al10Co25Cr8Fe15Ni36Ti6 compositionally complex alloy is known for its γ-γ′ microstructure and the third Heusler phase. Variations of this alloy, gained by replacing 0.5 or 1 at. pct Al by the equivalent amount of Mo, W, Zr, Hf or B, can show more phases in addition to this three-phase morphology. When the homogenization temperature is chosen too high, a eutectic phase formation can take place at the grain boundaries, depending on the trace elements: Mo and W do not form eutectics while Hf, Zr and B do. In order to avoid the eutectic formation and the potential implied grain boundary weakening, the homogenization temperature must be chosen carefully by differential scanning calorimetry measurements. A too low homogenization temperature, however, could impede the misorientation alignment of the dendrites in the grain. The influence of grain boundary phases and incomplete dendrite re-orientation are compared and discussed.

Abstract The post-dynamic recrystallization behavior of ultrafine-grained (UFG: 0.44 μm) cp-Ti under annealing, room temperature (RT) monotonic and cyclic loading was investigated across a range of temperatures and deformation rates wherever appropriate. By characterizing the grain and boundary structures, it was confirmed that recrystallization and grain growth occurred due to annealing (≥ 600 °C) and R = − 1 fatigue at RT. There was a noticeable 30 deg aggregation in misorientation distribution, along with the increased grain size. However, the hypothetical correlation between 30 deg aggregation and Σ13a or the other characteristic coincidence site lattice boundaries was found to be weak. The fatigue-induced grain growth is particularly intriguing for two reasons. First, the large monotonic deformation with low strain rate cannot trigger grain growth. Second, fatigue sharpened the basal intensity around the ND and caused a weaker texture component close to TD (load axis along the LD, perpendicular to the TD–ND plane). By contrast, high-temperature annealing only strengthened the UFG processing induced basal pole but without affecting its location. Novel insights into this fatigue-induced texture evolution in UFG cp-Ti has been provided. The lattice rotation during fatigue can be attributed to the combined effect of activation of prismatic $$ \langle a\rangle $$ ⟨ a ⟩ slip parallel to LD, and basal $$ \langle a\rangle $$ ⟨ a ⟩ slip perpendicular to it. The theoretically calculated stress to activate dislocation slip by assuming a non-equilibrium grain boundary state lent support to the above assertion. Moreover, the TEM observation evidently showed the characteristics of dislocation cross-slip and multiple slip in the grain interior. Graphical Abstract

Grain boundary engineering (GBE) of coatings using optimum weight fractions of foreign inclusions can improve corrosion resistance performance. This is illustrated here by correlating the corrosion behavior with the five-parameter grain boundary character distribution analysis of Zn-carbon nanotube (Zn-CNT) composite coatings. Zn-CNT composite coatings with different volume fractions of CNTs were electrodeposited on mild steel substrates by dispersing different amounts of CNTs (4, 6, 8, 10, 15, and 20 mg/L) in the Zn electrolyte bath. All the coatings exhibited compact and crack-free morphology. Electrochemical impedance spectroscopy (EIS) measurements were conducted in 3.5 wt pct NaCl solution. The Nyquist and Bode plots showed a decrease in the coating corrosion rate with initial CNT addition up to the Zn-CNT3 coating (produced from 8 mg/L of CNT in the electrolyte), after which the corrosion resistance decreased with continued addition of CNTs. This showed that an optimum exists for CNT in the Zn coating to achieve high corrosion resistance performance. Orientation distribution maps from the coating cross section were acquired using the electron backscatter diffraction (EBSD) technique for correlating the microstructure with the corrosion data. The lower corrosion rate in the Zn-CNT3 coating was attributed to the strong basal plane texture in grains along the growth direction. The angle/axis misorientation showed that most grain boundaries have [ $$ 2\overline{11} 0 $$ ] and [ $$ 10\bar{1}0 $$ ] axis misorientations signifying special grain boundaries. The five-parameter analysis showed that these grain boundaries are mostly symmetric and tilt boundaries, which are low-energy boundaries, whereas in Zn and Zn-CNT6 (produced from 20 mg/L of CNT in the electrolyte) coatings, the higher corrosion rates were due to the high fraction of high-angle grain boundaries (HAGBs), grain texture along the growth direction that corresponds to an orientation that is active in the corrosive environment, and the absence of special grain boundaries.

The slip/twinning activity and cracking behavior of an extruded Mg-3Y sheet during strain-controlled tension-compression low-cycle fatigue (LCF) at room temperature were studied quantitatively and statistically by slip trace analysis and EBSD-based misorientation analysis combined with SEM. The twinned area fraction was 1.7 pct after 200 cycles indicating that twinning contributed limited plastic deformation, and only tension twins were observed. Among 989 grains analyzed, 11.4 pct grains exhibited observable slip traces. Basal slip, with a relative frequency of 81.4 pct, was the dominant deformation mode, and pyramidal II slip (12.4 pct) also exhibited a high activity. The slip-dominated deformation was responsible for the symmetrical hysteresis loops. Among the total 311 cracks observed after 200 cycles, 80.1 pct were intergranular and 19.9 pct were transgranular. The appearance of the two kinds of cracks was closely related. Persistent slip band (PSB, 13.8 pct) and twin (TW, 5.5 pct) were two key transgranular crack initiation sites. The PSB cracking fraction (cracked PSBs/total PSBs) for different slip modes followed pyramidal II (64 pct) > basal (36 pct) > prismatic (14 pct). Strain localization was likely to be responsible for the high cracking fraction of pyramidal II PSBs, which was consistent with their small normalized Schmid factors and the heterogeneous distribution of geometrically necessary dislocation density. Slip/Twinning transfers at grain boundary were also occasionally observed and they were closely associated with transgranular cracks.

The application of dual phase steel in the automotive sector is increasing due to its high strength-to-weight ratio and good shock absorption capacity. The formability of dual phase steel is complex due to its multiphase microstructure which results in inaccurate formability prediction using numerical methods. The present study is aimed at analyzing the forming behavior and microstructure evolution of a dual phase steel, DP780, at different strain paths. The forming behavior of this steel was analyzed in terms of forming limit diagram (FLD) using Nakazima tests and finite element method. Various necking criteria were used to construct the FLD. Samples deformed at different dome height for three principal strain paths and strain levels were subjected to detailed microstructure and texture investigations. The microstructure and texture study was mainly focused on analyzing the development of deformation texture, misorientation development and orientation hardness. These studies showed that the formability of DP780 steel is largely affected by the development of γ fiber texture. Also, the evolution of other microstructure and texture quantifiers such as texture intensity, misorientation and relative orientation hardness at different strain paths was correlated with the formability of the material.

A clinoenstatite rim occurs in many refractory forsterite-rich objects; however, specialized studies of it have not been carried out. The first data from the study of refractory forsterite-rich objects by electron backscatter diffraction (EBSD) are reported. It is shown that the clinoenstatite rim in refractory forsterite-rich inclusions has a reactionary nature and was formed as a result of nebular processes. The rim is almost entirely composed of clinoenstatite. Forsterite grains have a block internal structure with a maximum misorientation angle of 10° within a single crystal.

The static recrystallization, nuclei orientations, and texture evolution of cold-rolled Mg–Zn–Gd alloys during annealing were tracked by quasi-in-situ electron backscatter diffraction method. An unusual texture transition from “rolling direction (RD)-split” to “transverse direction (TD)-split” occurred and oriented nucleation was observed. Nuclei originating from boundaries of the parent grain with “RD” orientation mainly exhibited “TD” orientations, and showed preferential misorientation relationship around 62.5° (including basal axes , , and ) with respect to the parent grain, which may be related to basal dislocations and low boundary energy.

Both ausforming and austempering below the martensite start temperature (MS) have been shown to accelerate the bainitic transformation. This work investigates the combined effects of deformation and austempering below the MS on the isothermal transformation kinetics, microstructure, and hardness in a medium-carbon bainitic steel. The results show that, deformation below the MS can delay the onset of the baintic transformation compared to the case in which no deformation is applied. The larger the amount of martensite presents prior to the deformation step, the greater the delay in the onset of bainitic transformation. This behavior is attributed to the development of strong misorientation gradients within austenite during the co-deformation of the austenite-martensite microstructure. These large misorientation gradients make the pre-existing martensite a less effective nucleation site for bainite.

The effects of three-stage homogenization on recrystallization and fatigue crack growth behavior of 7020 aluminum alloy were investigated. It was shown that a large amount of fine Al3Zr dispersoids form in the grain and near the grain boundaries of the alloy after three-stage homogenization. The ratio of volume fraction to radius for the Al3Zr dispersoids after three-stage homogenization increased by 171.2% compared with the one-stage homogenization. The recrystallization fraction was reduced from 29.5% for the one-stage homogenized alloy to 19.1% for the three-stage homogenized alloy. If the fatigue crack propagation encounters small recrystallized grains with high misorientation, the crack is easy to grow quickly along grain boundaries. When the stress intensity factor at the crack tip is 10MPa·m1/2, the fatigue crack growth rate (FCGR) of the one-stage homogenized alloy is 30.6% faster than that of the three-stage homogenized alloy.

A phase-field model for describing dynamic interactions between deformation twins and grain boundaries in a hexagonal close packed (HCP) metal is established. It is applied to simulating the coupled evolution mechanisms of grains and twins in magnesium (Mg) by probing the transmission of { 10 1 ¯ 2 } deformation twins across grain boundaries. We analyze the effect of the strain relaxation near a grain boundary, which is related to the geometric compatibility arising from the misorientation angle between adjoining grains. Phase-field simulations demonstrate that twin transmission across a grain boundary into a neighboring grain leads to grain boundary migration towards the neighboring grain with a reduced grain boundary width. The preferred nucleation site of new twin variant in the neighboring grain is related to the elastic interaction energy distribution. These predicted transmission behaviors agree well with existing experimental observations and molecular dynamics simulations. By analyzing set of systematic phase-field simulation results, we establish a rotation-angle-related twin variant selection rule for analyzing the transmission of { 10 1 ¯ 2 } deformation twins across grain boundaries in Mg and its alloys.

The disorder trapping induced by supercooling is innovated to promote the formation of chemically disordered solid solution phase in high-entropy alloy (HEA) when the ordered phase is more inclined to form. We design a new MoNbReTaW HEA, consisting of the top five refractory metals with the highest melting points, whose liquidus temperature attains 2788 K. It is featured with a very large negative enthalpy of mixing and a strong mismatch of atomic size. As a result of sluggish atomic diffusion under a sufficient supercooling up to 500 K and consequent disorder trapping at a crystal growth velocity of 15 to 25 m/s, the original single solid solution phase with a conspicuous local chemical ordering transforms into a chemically disordered state. Owing to the decrease of atomic size mismatch, not only the lattice is turned out to be well-aligned but also the dislocation density is reduced. By the supercooling-based rapid solidification approach under electrostatic levitation condition, we successfully achieved the growth of spherical single crystals with 2 to 3.5 mm in diameter and interior misorientation less than 2 angle degrees. The notable suppression of microsegregation helps to enhance the microhardness to 6.8 GPa at the maximum supercooling of 538 K. Disorder trapping contributes to the increase of nanohardness up to 11.2 GPa. The liquid supercooling is capable of strengthening the mechanical property by optimizing the local chemical ordering.

The surface roughening and martensitic phase transformation (MPT) of SUS 304 and SUS 316 were studied through two experiments: a uniaxial tensile stress test, repeated for five cycles, and an Scanning Electron Microscope&ndash, Electron Backscaterr Diffraction (SEM-EBSD) investigation. The MPT and martensitic volume fraction (Mf) were evaluated following the tensile test. The correlation between MPT, Mf, and surface roughening behavior was investigated. The experiment showed that an increase in the strain level from 0.4% to 1% increased the MPT and Mf, which transformed from a metastable austenitic phase in SUS 304. The increased strain level increased the surface roughening for various grain sizes (Dg), from fine grain (Dg &lt, 3 &mu, m) to coarse grain (Dg &ge, m). SUS 304 and SUS 316 are used so that the surface roughening mechanism between SUS 304 and SUS 316, with different phase conditions and at a similar Dg, can be determined. The results showed that the surface roughening increased for both fine and coarse grain at strain levels of 0.4% and 1%, however, a larger increase of surface roughening was obtained for coarse grain. In coarse grain, surface roughening increased significantly not only with a low MPT, but also with a low grain deformation. In coarse grain, the surface roughening increased proportionally to the strain level (&epsilon, p) because of the low MPT and weak grain. In fine grain, the surface roughening did not increase proportionally to the &epsilon, p because of the high MPT, which increased the grain strength in SUS 304. In the fine grain of SUS 304, the increase of surface roughening was nearly the same both at strain levels of 0.4% and 1%, because the MPT and Mf were nearly the same. The surface roughening with the same &epsilon, p and almost the same Dg in SUS 304 and SUS 316 fine grain was nearly the same, because the grain deformation almost produced the same relative inclination between neighboring grains in the initial state direction to the surface. The inter-grain movement changed the grain orientation. Based on kernel average misorientation (KAM) mapping, the local grain misorientation in SUS 304 was higher than that in SUS 316. This indicated that the fine-grain SUS 304 is harder than the fine-grain SUS 316. There is no MPT in SUS 316 because of the higher austenitic phase, which is affected by the austenitic former, such as Ni.

Ti-16.5Zr-13.5Cu-8.5Ni (wt.%) as a filler and brazing process as 950 °C/60 min were supplied in this study for brazing cast TiAl alloys with fully lamella structure. The interface microstructure and element diffusion were analyzed and measured by SEM, EBSD, and EPAM. And the mechanical properties of joints were evaluated. The sound joints were achieved with strength as 575 MPa at room temperature and remained as 410 MPa and 385 MPa in average at 700 °C and 760 °C, respectively. It was attributed to lots of fine grains with soft orientation as BCC [120] in the joint to the tensile direction. It was found that the fracture happened in the local zones with very large grains and the extreme misorientation between grains in the joint. Even though most grains as Ti3Al phase were found in the joint, there was no sign indicating the formed IMC related to the fracture.

The flat surfaces of a 7075 aluminum (Al) alloy plate were processed by sliding friction treatment (SFT), which is a technique for surface nanocrystallization of metals and alloys. The aim of this study was to investigate the microstructural evolution, mechanical behavior and strengthening mechanisms in this SFTed precipitation-strengthened Al alloy. The SFT resulted in a gradient structure (GS) with an effective depth of ~ 800 µm, and a nanostructured layer was formed within a depth of ~ 30 µm from the surface. Increasing boundary spacing and decreasing misorientation angle between boundaries were found with increasing depth from the surface, which was accompanied by a decrease in hardness from ~ 2436 MPa in the topmost surface layer to ~ 1568 MPa in the undeformed coarse grain (CG) matrix. Moreover, the GS revealed a prominent precipitate redistribution induced by the SFT. The GS revealed higher strength and especially exhibited a higher work-hardening rate at low strain (e < 0.026) than the CG, attributed to a novel coupling of dislocations, boundaries and precipitates. Grain boundary strengthening, dislocation strengthening, precipitation strengthening and synergetic strengthening in the GS were quantitatively evaluated based on sufficient discussion.

Mechanisms of grain refinement under multidirectional isothermal forging (MIF) at 325 °C (~ 0.65 Tm) and the strain rate 10− 4 s− 1 of the Al–Mg-based alloy with complex additions of transition metals were investigated. The starting alloy had an equiaxed grain structure with grain size 25 µm and a uniform distribution of coherent Al3(Sc,Zr) dispersoids of 20–50 nm. A distinguished structural feature in the early MIF stage was the formation of high strain- and misorientation gradients, followed by deformation banding. Due to the sequential changes of the loading axis, such bands were developed in various directions and fragmented the original grains. The number of bands and misorientation of their boundaries gradually rose with strain, resulting in formation of (ultra)fine grain structure with the grain size 2 µm. New grain formation was concluded to occur via continuous dynamic recrystallization and controlled by the nanosized precipitates, which preferably remained stable and coherent with the surrounding matrix.

A model describing the formation of a strain-induced facet at a high-angle boundary during its interaction with a dislocation pile-up is proposed in this work. The model of continuous dislocation distribution in a pile-up has been used to analyze the conditions under which a facet appears and to calculate its length as a function of the total Burgers vector of the dislocation pile-up and the boundary misorientation angle. The formation of a facet at a grain boundary is possible only if the total Burgers vector exceeds a certain critical value that depends on the external stress and boundary misorientation. The facet length as a function of the initial distance between a dislocation source and a grain boundary at various external stresses and misorientation angles has been calculated in the case of a pile-up replenished by a dislocation source. It is found that the material grain structure refinement and a shift of grain boundaries misorientation spectra into the region of large angles suppress strain induced grain boundary faceting. The facet formation has been shown to be accompanied by the formation of a shear band in the body of the adjacent grain.

In the present work, we report the observation of deformation kinking bands in β-treated commercial pure zirconium sheets during impact experiments. Crystallography analyses based on electron backscatter diffraction (EBSD) technique reveal that these kinking bands exhibit a common rotation axis of 〈 10 1 ¯ 0 〉 with misorientation angles varying in a wide range and are not belonging to anyone of the well-established twinning modes in Zr. Based on the combination of Schmid factor calculation and in-grain misorientation axes (IGMA) determination, the underlying mechanisms accounting for their formation are proposed and discussed.

The effect of grain boundary (GB) characteristics (as represented by misorientation angle) on its dynamic response is investigated by sampling a large set of 185 GBs in Ta bi-crystals. These GBs encompass both ordered and disordered structures – typically referred to as metastable structures, in order to reflect the diversity in the local atomic structure observed in realistic GBs. The results reveal four distinct regimes in damage distribution and failure modes as a function of misorientation angle. The above trends also correlate with the variation in the corresponding void nucleation stress.

The transformation behavior between iron oxides and oxyhydroxides like magnetite, hematite and goethite is still not entirely understood. Crystallographic similarities allow one to predict topotactic relationships between them. The related crystallographic aspects have been explored by means of electron backscatter diffraction (EBSD). Samples from natural aggregates of magnetite, hematite and goethite were collected from iron-formation rocks that outcrop in the southeast of Brazil, in a region known for large deposits of iron and other ores. EBSD misorientation data indicate a pronounced relationship between these iron phases. The transformation seems to be related to the oxygen framework. The original close-packed cubic arrangement of O atoms in magnetite changes to a hexagonal close-packed framework in hematite, i.e. {111} of magnetite is parallel to {0001} of hematite. The matrix in which the magnetite grains are embedded is made of aggregates of hematite and goethite. In the matrix, the coincidence observed in the magnetite grains is not observed. On the other hand, the well known twin boundary relationships already described for these mineral phases can be observed here as an orientation relationship in three-dimensional misorientation space. The spatial data of axis–angle pairs suggest that the twin boundaries serve as facilitating surfaces for phase transformation in the Fe–O–OH system. The main conclusion of this study is that the transformation occurred in the solid state with the newly transformed goethite inheriting the crystallographic orientations of the former crystals and that this phenomenon is better recognized by combining observations of misorientation relationships. In the matrix, such a relation is not observed and, for that reason, the minerals in the matrix are thought to have been formed by a different process, which might have involved dissolution and precipitation of the phase newly out of solution.

The evolution of sliver defect in a Ni-based single crystal superalloy was explored by casting samples with a similar geometry of the airfoil section of a turbine blade using optical microscope and electron backscattered diffraction. It was found that the sliver generally initiated from 1 to 2 tertiary dendrites at the diverging boundary between the mold wall and matrix. All slivers were tilt from matrix along the [001] and some of them rotated relative to the matrix on the plane perpendicular to the solidification direction. During solidification sliver in most castings grew with a fixed orientation. All slivers can extend along the solidification direction to the top of the casting. Most of the sliver defects showed constant width and did not extend on the casting surface. However, the sliver with large misorientation to matrix on the cross section perpendicular to the solidification direction extended on the casting surface and into the casting quickly.

Ferritic stainless steel (FSS 430) has been deformed by equal-channel angular pressing (ECAP) at room temperature at an equivalent strain (evm) of 1.2 by adopting the route Bc. Microstructural developments were studied by optical microscopy, transmission electron microscopy, and microtexture by electron backscattered diffraction. Typical ultrafine-grains of less 0.2 µm could be identified. The XRD patterns confirm the presence of a BCC phase alone. An increase in peak broadening is attributed to the reduction of crystallite size and increase of lattice strain arising from deformation during ECAP. The grain refinement takes place through simple shear deformation by elongation of grains, splitting of grains into bands, the subdivision of bands into subgrains by dynamic recovery, and conversion of subgrains into grains by progressive lattice rotation (PLR). Weakly textured rolled ferritic stainless steel is strongly textured at an imposed equivalent strain of 0.6 with the development of ideal shear components of D2θ and $$\bar{E}_{\theta }$$ for bcc materials. On the second pass of ECAP texture is partially randomized and the intensity of components was decreased and new components of D1θ and Fθ are developed due to subdivision of grains into bands, bands into subgrains, and conversion of subgrains into grains of high angle of misorientation by PLR. The yield strength, tensile strength, and hardness are increased almost 1.5 times that of as-received coarse-grained material due to a high degree of grain refinement and an increase in defect density or strain. The yield strength of 687 MPa of as-received material was enhanced to 1093 MPa of ECAPed ferritic stainless steel. However, the material has lost its ductility significantly due to high defect density and a significant amount of non-equilibrium nature of grain boundaries.

XtalCAMP is a software package based on the MATLAB platform, which is suitable for, but not limited to, the analysis and visualization of scanning Laue X-ray micro-/nanodiffraction data. The main objective of the software is to provide complementary functionalities to the Laue indexing software packages used at several synchrotron beamlines. The graphical user interfaces allow the easy analysis of characteristic microstructure features, including real-time intensity mapping for a quick examination of phase, grain and defect distribution, 2D color-coded mapping of microstructural properties from the output of other Laue indexing software, crystal orientation visualization, grain boundary characterization based on orientation/misorientation calculation, principal strain/stress analysis, and strain ellipsoid representation, as well as a series of additional toolkits. As an example, XtalCAMP is applied to the microstructural investigation of a solution-heat-treated Ni-based superalloy manufactured using a laser 3D-printing technique, and a deformed natural quartzite from Val Bregaglia in the Central Alps.

The present research investigated the effect of annealing temperature on surface gradient fine microstructure and wear resistance of low-carbon steel. The results depicted that the optimized annealing temperature from 300 °C to 400 °C can facilitate the formation of a stable fine microstructure. The fine grain size is about 0.2 μm on the topmost surface layer, and the percentage of grain boundary with misorientation angle of 1.5° is 26 %. The full width at half maximum values gradually decreases with increasing temperature from room temperature to 600 °C. In addition, the abrasive wear dominates the entire process for samples annealed at 300-400 °C. The wear mechanism gradually switches to adhesive wear and even delamination wear when the annealing temperature is increased to 500-600 °C.