Grain Orientation Spread Research Articles

Microstructure Characteristics and Identification of Low-Carbon Steels Fabricated by Controlled Rolling and Accelerated Cooling Processes

In the present study the microstructure of low-carbon steels fabricated by controlled rolling and accelerated cooling processes was characterized and identified based on various microstructure analysis methods including optical and scanning electron microscopy, and electron backscatter diffraction(EBSD). Although low-carbon steels are usually composed of α-ferrite and cementite(Fe3C) phases, they can have complex microstructures consisting of ferrites with different size, morphology, and dislocation density, and secondary phases dependent on rolling and accelerated cooling conditions. The microstructure of lowcarbon steels investigated in this study was basically classified into polygonal ferrite, acicular ferrite, granular bainite, and bainitic ferrite based on the inverse pole figure, image quality, grain boundary, kernel average misorientation(KAM), and grain orientation spread(GOS) maps, obtained from EBSD analysis. From these results, it can be said that the EBSD analysis provides a valuable tool to identify and quantify the complex microstructure of low-carbon steels fabricated by controlled rolling and accelerated cooling processes.

Deformation Zone Length and Plastic Strain in Twin-Roll Casting of Strips of Al-Mg-Si Alloy

An original method for determination of the deformation zone length and corresponding plastic strain is suggested. The method is based on microstructural analysis of wedge-shaped specimens produced by controlled rapid process interruption. Electron backscatter diffraction analysis followed by grain orientation spread (GOS) characterization allows description of the grain evolution during the passage through the roll gap. The appearance of the first elongated grains and increase in GOS values detected in the microstructure of the strip core zone were used for exact identification of the deformation zone origin.

Dynamic Recrystallization of the Constituent γ Phase and Mechanical Properties of Ti-43Al-9V-0.2Y Alloy Sheet.

A crack-free Ti-43Al-9V-0.2Y alloy sheet was successfully fabricated via hot-pack rolling at 1200 °C. After hot-rolling, the β/γ lamellar microstructure of the as-forged TiAl alloy was completely converted into a homogeneous duplex microstructure with an average γ grain size of 10.5 μm. The dynamic recrystallization (DRX) of the γ phase was systematically investigated. A recrystallization fraction of 62.5% was obtained for the γ phase in the TiAl alloy sheet, when a threshold value of 0.8° was applied to the distribution of grain orientation spread (GOS) values. The high strain rate and high stress associated with hot-rolling are conducive for discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), respectively. A certain high-angle boundary (HAGB: θ = 89° ± 3°<100>), which is associated with DDRX, occurs in both the recrystallized and deformed γ grains. The twin boundaries play an important role in the DDRX of the γ phase. Additionally, the sub-structures and sub-boundaries originating from low-angle boundaries in the deformed grains also indicate that CDRX occurs. The mechanical properties of the alloy sheet were determined at both room and elevated temperatures. At 750 °C, the alloy sheet exhibited excellent elongation (53%), corresponding to a failure strength of 467 MPa.

Overcoming the drawbacks of plastic strain estimation based on KAM

Plastic strain estimation using electron backscatter diffraction (EBSD) based on kernel average misorientation (KAM) is affected by random orientation measurement error, EBSD step length, choice of kernel and average grain size. These sensitivities complicate reproducibility of results between labs, but it is shown in this work how these drawbacks can be overcome. The modifications to KAM were verified against a similar misorientation metric based on grain orientation spread (GOS), which does not show sensitivity to these factors. Both metrics were used in parallel to estimate the plastic strain distribution in Alloy 690 heat affected zones from component mockups, and showed the same results where the grain size was correctly compensated for.

EBSD法によるクリープ損傷評価のためのラウンドロビン試験

Crystal orientations of creep damaged Type 316 stainless steel (SUS316L) were measured by 3 organizations using the same specimens, passed in a round robin, in order to investigate the scatter in material damage assessment using the electron backscatter diffraction (EBSD) technique. Two misorientation parameters, KAM (Kernel average misorientation) and GOS (Grain orientation spread), were calculated using mapping data of measured crystal orientations. It was shown that KAM and GOS correlated well with the degree of creep strain. However the scatter in GOS was smaller than in KAM. The GOS parameter showed an excellent correlation with both of the creep strain and creep damage ratio. It was concluded that the GOS parameter can be used for evaluation of the creep damage. The empirical relationship between GOS parameter and the degree of the creep damage can be shared regardless of the SEM/EBSD system used.

XRDおよびEBSDを用いた23Cr-45Ni-7W合金溶接部のひずみ評価

The residual strain of 23Cr-45Ni-7W Alloy welds was estimated by the change in the dislocation density and the average misorientation within grains. X-ray diffraction was used to measure the dislocation density by the modified Williamson-Hall method and the modified Warren-Averbach method. EBSD technique was used to measure the orientation in order to calculate the grain orientation spread (GOS) as the average misorientation within grains. Tensile tests were conducted at room temperature and were interrupted to prepare a number of specimens with different residual strain. The changes in the dislocation density and GOS with the strain were investigated using the interrupted specimens and the heat-affected zone in 23Cr-45Ni-7W Alloy welds. The dislocation density and GOS increased approximately linearly with increase in the residual strain. The residual strain of the heat-affected zone in 23Cr-45Ni-7W Alloy welds was evaluated from the linear relationships. The residual strain near the bond line estimated by the dislocation density was 3.7%;the estimated residual strain decreased with increases in the distance from the bond line. At 10 mm away from the bond line, the residual strain became less than 1%. The change in the residual strain near the bond line estimated by GOS showed a similar tendency.

純鉄圧粉磁芯の保磁力に及ぼす微視組織の影響

The recrystallization behavior of pure iron powder cores during the annealing process core is visualized with the Grain Orientation Spread (GOS) map from an SEM/EBSD analysis, and found to be significantly inhomogeneous, leading to an inhomogeneous dislocation density distribution. Nevertheless, a conventional dislocation pinning model well describes the coercive force behavior if the average dislocation density is applied. The pinning model is modified to separate the influence of the grain boundary pinning, and the relationship between the coercive force and the microstructure is discussed comprehensively.

Recrystallization Behavior of Aluminum Plates Depending on Their Purities

Recrystallization behavior has been investigated for commercial purity AA1050 (99.5wt%Al) and high purity 3N Al (99.9wt% Al). Samples were cold rolled with 90% of thickness reduction and were annealed isothermally at 290, 315, and 350oC for various times until complete recrystallization was achieved. Hardness measurement and Electron Backscatter Diffraction(EBSD) analyses, combined with Grain Orientation Spread(GOS), were employed to investigate the recrystallization behavior. EBSD analysis combined with GOS were distinctly revealed to be a more useful method to determine the recrystallization fraction and to characterize the recrystallization kinetics. As the annealing temperature increased, recrystallization in AA1050 accelerated more than that process did in Al 3N. Both AA1050 and Al 3N showed the same temperature dependence of the n value of the Johnson-Mehl-Avrami-Kolmogorov equation(JMAK equation), i.e., n values increased as annealing temperature increased. Activation energy of recrystallization in AA1050 is about 176 kJ/mol, which is comparable with the activation energy of grain boundary migration in cold-rolled AA1050. This value is somewhat higher than the activation energy of recrystallization in Al 3N.

Mechanism of continuous dynamic recrystallization in a 50Ti-47Ni-3Fe shape memory alloy during hot compressive deformation

The mechanisms of dynamic recrystallization (DRX) in a 50Ti-47Ni-3Fe alloy are studied using compression tests at temperatures of 1023–1323 K with strain rates of 0.01–10 s−1, and the resulting stress-strain curves are used to construct an Arrhenius equation with a Zener-Hollomon parameter (Z). The relationship between this Z parameter and stress, and its effect on the subgrain size are discussed. With the help of electron backscatter diffraction (EBSD), the development of recrystallizing grain boundaries is tracked in deformed grains with different grain orientation spread (GOS) values. Continuous dynamic recrystallization (CDRX) is subsequently confirmed by evidence of the conversion of low-angle boundaries (LAGBs) into high-angle boundaries (HAGBs). Grain boundary sliding (GBS) and HAGB migration are therefore considered secondary mechanisms under high-Z (ln Z > 29) and low-Z (ln Z < 23.5) conditions, but CDRX is confirmed as the dominant DRX mechanism.

Microstructural evolution and mechanical properties on an ARB processed IF steel studied by X-ray diffraction and EBSD

Accumulative Roll Bonding (ARB) is one of the so-called severe plastic deformation (SPD) processes, allowing the production of metals and alloys with ultrafine (micro-nano) structures. Materials with ultrafine grains present attractive properties like the simultaneous increase in strength and ductility. Our interest in these materials is focused on their microstructural evolution during ARB processing, eventually responsible for the enhancement of those mechanical properties.In the current work we follow the evolution of the microstructure in an interstitial-free (IF) steel deformed by ARB after consecutive processing cycles, by means of Electron BackScatter Diffraction (EBSD) and X-ray diffraction (XRD). Particularly, we present results related to texture, grain (GS) and domain sizes, grain boundary character, density of Geometrically Necessary Dislocations (GND), Grain Orientation Spread (GOS), lattice parameters, microstrain, dislocation density and their spatial arrangement.After 5 ARB cycles the system shows a microstructure constituted mainly by submicrometric grains with high angle boundaries and low presence of dislocations inside the grains.

Strain hardening of Titanium alloy Ti6Al4V sheets with prior heat treatment and cold working

Strain hardening of Titanium alloy Ti6Al4V has been studied at four different strain rates (10−4 to 10−1s−1) under tensile loading at four different heat treatment conditions viz. mill annealing (MA), recrystallization annealing (RA), solution treatment (ST) and solution treatment and aging (STA). Effect of prior cold working before tensile testing has also been studied. Strain hardening exponent (n) is found to be decreasing with increasing strain rates for samples in all the four heat treatment conditions, whereas trend is found to be opposite in case, of cold worked (~15%) samples prior to tensile testing. This is due to rearrangement of dislocations generated during the prior cold working. Strength coefficient (K) is also found to follow similar trend.Optical microstructure clearly showed two phase (α+β) structure in all the samples and completely fragmented grain boundaries in cold worked condition. Non-basal oriented grains in as-annealed samples and higher volume fraction of basal (0001) grains in annealed and cold worked samples were observed along with fragmented grain boundaries/regions of void coalescence. Low angle misorientation was found to be lower in sample subjected to STA heat treatment as compared to other heat treated conditions. Twinning was observed in ST as well as in STA conditions, which was absent in annealed as well as annealed and cold worked samples.Image quality maps revealed regions of low image quality in deformed samples indicating presence of high dislocation density. Regions of void coalescence were confirmed by KAM (Kernel average misorientation) maps, GOS (grain orientation spread) maps and unique grain colour maps. Analysis of fractographs showed ductile mode of fracture in all heat treated conditions and mixed mode of fracture with fragmented grain boundaries in all samples subjected to heat treatment followed by tensile testing with prior cold working.

In-situ study on the self-annealing behavior of electroplated Cu through the cantilever method, XRD, and EBSD

Abstract It is well-known that self-annealing of as-electroplated Cu would cause remarkable microstructure transition in few hours, inducing grain growth accompanied by elimination of grain boundaries and redistribution of impurities and crystallographic defects that determine the physical/chemical characteristics (e.g., resistivity and internal stress) of the entire Cu film. We carried out an in-situ study on this strongly time-dependent phenomenon to probe into crystallographic/microstructure and strain transitions in the self-annealing procedure. The crystallographic evolution of electroplated Cu, including grain size distribution, crystallographic orientation, grain boundaries, and residual strain, were investigated by means of in-situ X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). Moreover, grain orientation spread (GOS) value was obtained via the EBSD analysis, which offers valuable information regarding the residual strain distribution in the Cu platings. The internal stress of electroplated Cu was examined via a cantilever method. Additionally, effects of self-annealing on the impurity redistribution were investigated by a time of flight secondary ion mass spectrometer (TOF-SIMS). The knowledge advances our understanding of the evolution of the electroplated Cu physical/chemical properties during self-annealing.

Evaluation of Microstructure and Magnetic Properties in Non-oriented Electrical Steel Strained by Tension

The effects of deformation on the microstructure and magnetic properties of non-oriented electrical steels were investigated. Box-annealed electrical steel sheets were deformed by tension at four different strains: 3%, 8%, 12% and 25%. The internal grain misorientation caused by tensile deformation was measured by electron backscattering diffraction (EBSD) with grain orientation spread (GOS) as an indicator of the lattice distortion. The experimental results showed that the average GOS value increases with the strain. The microstructure and crystallographic texture of deformed samples did not show a significant change in samples strained below 25%. However, the magnetic properties were strongly affected: coercivity was directly proportional to the square root of the GOS value and energy losses increased as the strain level was increased.

Investigation of SIBM driven recrystallization in alpha Zirconium based on EBSD data and Monte Carlo modeling

The work focuses on the influence of moderate plastic deformation on subsequent partial recrystallization of hexagonal zirconium (Zr702). In the considered case, strain induced boundary migration (SIBM) is assumed to be the dominating recrystallization mechanism. This hypothesis is analyzed and tested in detail using experimental EBSD-OIM data and Monte Carlo computer simulations. An EBSD investigation is performed on zirconium samples, which were channel-die compressed in two perpendicular directions: normal direction (ND) and transverse direction (TD) of the initial material sheet. The maximal applied strain was below 17%. Then, samples were briefly annealed in order to achieve a partly recrystallized state. Obtained EBSD data were analyzed in terms of texture evolution associated with a microstructural characterization, including: kernel average misorientation (KAM), grain orientation spread (GOS), twinning, grain size distributions, description of grain boundary regions. In parallel, Monte Carlo Potts model combined with experimental microstructures was employed in order to verify two main recrystallization scenarios: SIBM driven growth from deformed sub-grains and classical growth of recrystallization nuclei. It is concluded that simulation results provided by the SIBM model are in a good agreement with experimental data in terms of texture as well as microstructural evolution.

Comparison of Room Temperature and Cryo-Deformation Effects on Mechanical Properties and Microstructure of Copper

The objective of this work is to study the effect of room temperature (RT) and liquid nitrogen temperature (LNT) rolling on mechanical properties of the pure copper. For the same percentage deformation, LNT samples show a significant increase in tensile strength and hardness value compared to RT samples. Microstructural investigation shows a large misorientation change between RT and LNT samples when we use grain orientation spread (GOS) as a measure of microstructural change. The mechanical property and microstructural changes are correlated with calorimetry experiments. We also present some preliminary results from our work on wire drawing at RT and LNT.

Research on the hot deformation behavior of a Fe–Ni–Cr alloy (800H) at temperatures above 1000 °C

Considering the pinning effect of fine carbides on grain boundaries, hot compression tests were performed above the dissolution temperature of Cr23C6 to investigate the hot deformation behavior of a Fe–Ni–Cr alloy (800H). The results show that the single peak stress associated with dynamic recrystalization (DRX) became more distinct at higher temperature and lower strain rate. The process of DRX was thoroughly stimulated when deformed above 1000 °C. Constitutive equations for hot deformation were established by regression analysis of conventional hyperbolic sine equation. The relationships between Zener–Hollomon parameter (Z) and the characteristic points of flow curves were established using the power law relation. Furthermore, kernel average misorientation (KAM) and grain orientation spread (GOS) were used to map the distribution of local misorientation and estimate the fraction of DRX, respectively. The critical strain and peak strain were used to predict the kinetics of DRX with the Avrami-type equation.

Grain Size and Texture Evolution During Annealing of Non-oriented Electrical Steel Deformed in Tension

The evolution of grain size and texture during annealing at 700 °C of a low C, Si-Al electrical steel strip is investigated in samples deformed between 3 and 25% in tension. After an incubation period, which decreases as the magnitude of the pre-deformation increases, the grain size-time relationship exhibits two different stages. Initially, the grain growth occurs in some especial grains until they consume the deformed microstructure. In contrast, during the second stage the rate of growth decreases rapidly and a final constant grain size is reached which depends strongly on the initial deformation. Analysis of EBSD data obtained from strained samples shows that there is a direct relationship between the magnitude of the prior tensile strain, the intergranular misorientations as estimated by the grain orientation spread (GOS) and the image quality parameters. An attempt to explain the recrystallization texture observed in terms of the Taylor factors for some orientations in the α fiber of the deformation textures was made, nevertheless this analysis was not entirely satisfactory. However, it was found that the main orientation components present in the recrystallization texture of annealed samples are those with lower internal misorientation (lower GOS) in the deformed material. These results suggest that, in the material investigated, recrystallization after tensile deformation takes place via strain-induced boundary migration during annealing. Estimation of energy losses due to magnetic hysteresis in annealed samples show that the energy losses decrease as the grain size increases and as the texture factor defined as the ratio between the volume fractions of detrimental and beneficial orientations for magnetic properties, \(f\{ 111\} + f(112)[1\overline{1}0] + f(110)[1\overline{1}0])/f\{ 001\}\), increases.

SEM/EBSD法を用いたオーステナイトステンレス鋼のクリープひずみ評価

Changes of misorintation in grains were studied by Scanning Electron Microscopy and Electron Back Scattering Diffraction (SEM/EBSD) for austenitic stainless steel, SUS 316 that were crept under 100 MPa at 973K. Misorientation of the specimens was calculated by Kernel Average Misorientation (KAM), Grain Average Misorientation (GAM) and Grain Orientation Spread (GOS). The values calculated by KAM, GAM and GOS increased with the strain increasing linearly during the transient creep stage. The tendency corresponded to the changes in total dislocation density estimated by Transmission Electron Microscopy (TEM). In the transient creep stage, good linearity between geometrically necessary (GN) dislocation estimated from KAM values and dislocation density by TEM was revealed. Compared the increments among misorientations calculated by KAM, GAM and GOS, one of GOS was the highest and the others were almost the same. Increments of KAM values were lower than those reported in the previous papers. Because data was obtained from the crept specimens in this study but data were obtained from specimens deformed in room temperature or moderate temperature. It was suggested that the increment of GN dislocation become lower due to dynamic recovery during creep test in this study. When the pitches in the EBSD measurement were taken account into, the increment of GAM values in this study was equal to one reported in the previous paper where the data was obtained from the crept specimens of stainless steel with the similar grain size.

Mechanical properties and deformation behaviour of Fe-(20/27)Mn-4Al-0.3C austenitic steels

The mechanical properties of the Fe-20Mn-4Al-0.3C (20Mn) and Fe-27Mn- 4Al-0.3C (27Mn) austenitic steels are investigated, and the deformation behavior under uniaxial tension was analysed. The 20Mn steel displays superior tensile properties to steel 27Mn, but the latter has a higher work hardening rate at the onset of deformation. The medium stacking fault energy (SFE) of the two steels impedes the boom of deformation twinning and promotes the appearance of microbands in the late stage of straining, so that the work hardening rate is monotonously diminishing and fails to rise again. The maximum volume fraction of twin lamellae is less than 8 vol.%, and their mean spacing was also estimated. The distribution of grain orientation spread (GOS) indicates that twinning process contributes to relieving the locally high distortion generated by the dislocation cross-slip inside the grains, which improves the uniform plasticity. The 27Mn steel keeps a much higher toughness than 20Mn steel for each temperature. The Charpy impact energy of steel 27Mn after annealing reaches 310J and 188J at room temperature and −196 ◦ C, respectively.

Investigations of the microstructural response to a cold forging process of the 6082-T6 alloy

The microstructure of 6082 aluminium alloy in artificial aged condition was investigated before and after cold forming. The cold forming process was performed at room temperature with and without lubricant. An in depth microstructure investigation has been carried out through electron backscatter diffraction (EBSD) analysis. Different approaches were considered to quantify the plastic strain: the Line Segment Method (LSM) and the study of misorientations trough the Kernel Average Misorientation (KAM), the Grain Orientation Spread (GOS) and the Grain Average Misorientation (GAM). The evidence of intermetallic particles removal from their location during plastic deformation was observed. Values of plastic strain lower than 0.1 did not affect the grain size itself. Nonetheless it induced the development of sub-structures which may lead to the hardening of the alloy.