Inverse Pole Figures Research Articles

Inhomogeneous strain and recrystallisation of a shot-peened Inconel 625 alloy after annealing

ABSTRACTMicrostructural variations in a shot-peened nickel superalloy after isothermal annealing were observed via scanning electron microscopy and electron backscatter diffraction analysis. The analysis was based on inverse pole figure and kernel average misorientation maps. Before annealing, a heavily plastically deformed layer was observed under the surface. Post annealing for 1 h, the uppermost 30–40 µm layer was discontinuously recrystallised and inhomogeneous strains remained in the below layers. After a particular duration, the inhomogeneous strains recovered but did not recrystallise. The threshold depth of recrystallisation depended on the inhomogeneous strains. Recrystallisation and growth progressed from the recrystallisation-threshold depth toward the surface. These microstructural variations explain the release mechanism of the residual stress induced by shot peening.

Study of the anisotropy of the polycrystal properties based on texture data

The results of studying correlation between the crystallographic texture of polycrystalline materials and anisotropy of their physical and mechanical properties are considered. The methods for calculating the anisotropic properties of polycrystals based on the data obtained by X-ray methods of direct and inverse pole figures are reviewed. Calculation methods based on the use of the distribution function of crystallite orientations require the use of a large amount of experimental data and, hence, they are not suitable for express estimation of the anisotropy level of the physical properties of samples upon their thermomechanical processing. A method for rapid estimation of the anisotropic properties of the sample based on the use of Д; ("orientation factors") in the calculations, is proposed. Experimental data of X-ray analysis (method of inverse pole figures) are used to calculate the absolute and relative deviations of the physical parameter of textured polycrystal from the same value in the isotropic sample. The contributions of individual crystallographic orientations to the formation of the anisotropy of the properties of the sample are estimated. The dynamics of quantitative changes in the anisotropic properties of a polycrystal in the process of texture formation is studied. To analyze the source of the most rapid changes in the anisotropy of properties, we used the coefficients of the "response" matrix, the calculation of which does not depend on the results of specific diffractometric measurements, but is common for all metals with a hexagonal close-packed (hep) lattice. The anisotropy of the coefficient of thermal conductivity, electrical conductivity, and thermal diffusivity was calculated for the samples of deformed yttrium which underwent cold rolling with a reduction ratio of e = 25%. It is shown that the final physical properties_of the hep polycrystal are largely determined by the pyramidal crystallographic orientations {1015}, {1124}. The results of the study form a basis for analysis of the anisotropy of the physical properties of hep-metal samples upon thermomechanical processing.

Metallographic, structural and mechanical characterization of low-density austenitic Fe-Mn-Al-C steels microalloyed with Ti/B and Ce/La in hot-rolling condition

ABSTRACTLow-density austenitic Fe-Mn-Al-C steels have high strength, high ductility and a significant weight reduction respect to other alloyed steels. However, this complex system exhibits second-phase precipitation, particularly κ-carbide. It is well-known that the microalloying elements addition to steel generates precipitation hardening, as well as grain refinement effect. It is worth noting that low-density steels can cause cracking during hot-rolling due to high Mn, Al and C contents and segregation in grain boundaries. Hot-rolling conditions play an important role in the dynamic recrystallization mechanisms, and therefore in the austenitic grain size. The main objective of this research work is the metallographic, structural and mechanical characterization of low-density steels microalloyed with Ti/B and Ce/La in hot-rolling condition. For this purpose Fe-(27-30)Mn-(7-8)Al-(1.2-1.8)C (wt.%) low density steels microalloyed with Ti/B and Ce/La were hot-rolled at 1200 °C in two stages. Metallographic, structural and mechanical characterization was carried out by optical (LOM) and scanning electron (SEM) microscopies, electron backscatter diffraction (EBSD) through quality images, inverse pole figures (IPF) and orientation distribution functions (ODF) maps, X-ray diffraction (XRD) and microhardness Vickers (HV) testing. In general, the first stage of hot-rolling exhibits a strongly bimodal microstructure of dynamically recrystallized austenitic grains, while the second stage shows more uniform recrystallized grain size. In the first stage of hot-rolling the austenite is the predominant phase, while in the second stage the α-ferrite phase is barely visible. Low-density steel microalloyed with Ti/B presented better grain size and microhardness values compared to steel microalloyed with Ce/La. Preferred crystallographic orientations were not found.

Local Crystal Misorientation Influences Non-radiative Recombination in Halide Perovskites

We use ultrasensitive electron backscatter diffraction (EBSD) to map the local crystal orientations, grains, and grain boundaries in CH3NH3PbI3 (MAPI) perovskite thin films. Although the true grain structure is broadly consistent with the morphology visible in scanning electron microscopy (SEM), the inverse pole figure maps taken with EBSD reveal grain structure and internal misorientation that is otherwise hidden. Local crystal misorientation is consistent with the presence of local strain which varies from one grain to the next. We acquire co-aligned confocal optical photoluminescence (PL) microscopy images on the same MAPI samples used for EBSD. We correlate optical and EBSD data, showing that PL is anticorrelated with the local grain orientation spread, suggesting that grains with higher degrees of crystalline orientational heterogeneity (local strain) exhibit more non-radiative recombination. We find that larger grains tend to have larger grain orientation spread, consistent with higher degrees of strain and non-radiative recombination.

TiB whiskers stimulated the dynamic recrystallization behavior

B-containing high temperature titanium alloys were in situ fabricated successfully by casting route. The influences of heat treatment processes on the evolution of microstructures, textures, strengths, elongations and fracture characteristics at room temperature (RT) and high temperature (650 °C) were analyzed. Microstructure investigation revealed that TiB whiskers stimulated the dynamic recrystallization behavior. The volume fractions of primary α phase (VPα) decreased with the increasing solution temperature, while the volume fractions of transformed β phase (VTβ) and widths of secondary α lamellas in transformed β phase (WSα) increased. The inverse pole figures (IPFs) observations illustrated near-equiaxed α grains transformed to ideal equiaxed morphology after 960 °C solution. By the analyzation of pole figues (PFs), after α+β heat treatments, the overall texture intensity increased with the increasing solution temperature, and after β heat treatments, textures with comparatively high intensities were concentrated around various directions. The equiaxed α grains and lamellar α phase had similar main texture components. But the maximum texture intensity of lamellar α phase was obviously higher than that of equiaxed α grains. Moreover, the textures of equiaxed α gains and lamellar α phase exhibited higher similarity after 980 °C solution comparing with after 960 °C solution. Alloy after 980 °C solution exhibited an excellent combination of RT and 650 °C mechanical properties which was ascribed to the microstructure tailoring and the load-sharing effect of TiB whiskers. Fracture of alloys was due to the debonding of TiB whiskers, and the growth and coalescence of micro-voids in matrix and around the cracks of fractured TiB whiskers.

Investigation of reorganization of a nanocrystalline grain boundary network during biaxial creep deformation of nanocrystalline Ni using molecular dynamics simulation.

In this paper, simulated biaxial creep deformation behaviour for nanocrystalline (NC) nickel (Ni) has been performed at various applied load (i.e. 1GPa, 1.4GPa, 2GPa, 2.5GPa and 3GPa) for a particular temperature (i.e. 1210K) using molecular dynamics (MD) simulation to investigate underlying deformation mechanism based on the structural evolution during biaxial creep process. Primary, secondary and tertiary stages of creep are observed to be exhibited significantly only at 3GPa applied stress. While, only primary and secondary stages of creep are exhibited at 1GPa applied stress. Atomic structural evaluation, dislocation density, shear strains, atomic trajectory, inverse pole figures and grain orientation with texture distribution have been carried out to evaluate structural evolution. Stress exponent (m) for NC Ni is analysed for a particular creep temperature (i.e. 1210K) and obtained m value is 1.30. According to shear strains counter plot, accumulation of higher shear strains are observed at grain boundary (GB) during biaxial creep deformation. It is found that dislocation density during biaxial creep is increased with the progress of creep process. Grain rotation and texture evaluation during biaxial creep process are studied using grain tracking algorithm (GTA). Grain rotation in ultrafine-grained NC Ni specimen during biaxial creep deformation is happened and exhibits almost distinct distribution, which is occurred due to the atomic shuffling within the GBs. Grain growth of ultrafine grained NC Ni is observed during biaxial creep deformation which is caused by mechanical stress.

Selected Area Electron Diffraction, a technique for determination of crystallographic texture in nanocrystalline powder particle of Alloy 617 ODS and comparison with Precession Electron Diffraction

Texture analysis in nanocrystalline materials is a challenge. A simple technique as Selected Area Electron Diffraction (SAED) has been used to evaluate texture in a single nanocrystalline Alloy 617 ODS powder particle by carrying out Rietveld texture refinement using Material Analysis Using Diffraction (MAUD) software package and the results were compared with the ASTAR™/Precision Electron Diffraction (ASTAR™/PED) results. Extraction of texture from the SAED patterns involved image analysis and Rietveld refinement of radial plots divided into judiciously chosen angular spans. Inverse pole figure (IPF) from SAED pattern using MAUD revealed 〈110〉 texture parallel to the normal direction (electron beam direction) for unmilled and 6 h milled powders. IPF from ASTAR™/PED technique also shown 〈110〉 lying parallel to the normal direction (beam direction) in both unmilled and the 6 h milled powder. A one is to one correspondence of IPF obtained from MAUD to that of ASTAR™/PED was observed. Texture in unmilled powder could be attributed to the compressive force during rapid solidification in water atomisation process. During the milling process, inhomogeneous rolling and compression of the trapped powder particle in between the balls and between the balls and walls of the jar resulted in shear texture in 6 h milled powder. ASTAR™/PED technique also showed the presence of 〈100〉 //ND texture which was attributed to solidification in unmilled powder and 〈112〉 //ND type texture in milled powder attributed to twin mode of deformation during milling.

Crystallographic orientation dependence of mechanical properties in the superelastic Ti-24Nb-4Zr-8Sn alloy

Nanoindentation and electron backscattered diffraction techniques are used to study the dependence of crystallographic orientation on mechanical properties in individual grains of the superelastic polycrystalline Ti-24Nb-4Zr-8Sn alloy. Strain recovery, elastic modulus, and hardness are evaluated from the force-displacement curves using spherical and Berkovich indenters. Experimental data are reported in a standard stereographic triangle covering all possible crystallographic directions of loading in the bcc-\ensuremath{\beta} structure of the Ti-24Nb-4Zr-8Sn alloy. Our experiments show that both spherical and Berkovich indenters are suitable for probing anisotropy of elastic modulus whereas spherical indenter is more appropriate for probing anisotropy of superelastic response. The highest indentation strain recovery is measured along $\ensuremath{\langle}001{\ensuremath{\rangle}}_{\ensuremath{\beta}}$ and the lowest one is observed along $\ensuremath{\langle}111{\ensuremath{\rangle}}_{\ensuremath{\beta}}$. Our inverse pole figure distribution of indentation strain recoveries is in good agreement with inverse pole figure distribution of compressive lattice distorsions calculated from the crystallographic model of martensitic transformation in \ensuremath{\beta} titanium alloys. This established pattern in compression is very different from that seen during tensile deformation, and both our experiments and calculations confirm the strong tension-compression asymmetry of the strain response in superelastic \ensuremath{\beta} titanium alloys. The indentation modulus also shows significant crystallographic anisotropy: ${E}_{[001]\ensuremath{\beta}}<{E}_{[101]\ensuremath{\beta}}<{E}_{[111]\ensuremath{\beta}}$. In contrast, orientation dependence is lost when plasticity has set in, and hardness becomes independent of crystallographic orientation due to the fact that multiple directions are prone to generate slip systems in the bcc-\ensuremath{\beta} structure.

Ag–Pd–Cu alloy reflector to improve the opto-electrical performance and electromigration resistance of near ultraviolet GaN-based light-emitting diode

We investigated the opto-electrical and electromigration properties of near ultraviolet light emitting diodes (UV-LEDs) fabricated with Ag–Pd–Cu (APC) and Ag only reflectors. It was shown that unlike Ag only sample, the APC sample revealed a smooth surface with hillocks when annealed at 600 °C. The 600 °C-annealed APC sample gave a reflectance of 84.2% at 400 nm, whereas the Ag sample had 69.0%. Both the samples exhibited ohmic behavior when annealed. The specific contact resistivity of the Ag and APC contacts annealed at 500 °C were estimated to be 2.59 × 10−4 and 1.85 × 10−4 Ωcm2, respectively. The X-ray photoemission spectroscopy Ga 2p core level results showed that for the annealed APC sample, the Ga 2p core level was shifted towards the lower binding-energies by 0.67 eV as compared to that of the as-deposited sample. Both UV-LEDs with the 500 °C-annealed Ag and APC reflectors gave the same forward voltage of 3.23 V at 20 mA. The UV-LED with the annealed APC reflector yielded 9.07% higher output at 100 mA than that with the annealed Ag reflector. The APC sample exhibited a longer median-time-to-failure (MTF) by a factor of 1.4 than the Ag sample. The activation energy for the electromigration of these samples was measured to be 0.58–0.7 eV. Electron back scatter diffraction (EBSD) and inverse pole figure (IPF) images revealed that the Ag sample was more <111>-textured than the APC sample. Based on the scanning electron microscopy, EBSD and IPF results, the better thermal and electromigration properties of the APC sample are described and discussed.

Improved Output Power Behavior of Ultraviolet GaN-Based Light-Emitting Diode By Using Agpdcu Reflector

GaN-based ultraviolet UVLEDs have attracted a great deal of interest because of their applications in water and air purification and solid-state lighting. These applications have stimulated the technological development of high-efficiency UVLEDs. On the one hand, UVLEDs exhibit relatively lower external quantum efficiencies (EQEs) than visible LEDs. In particular, high-power UVLEDs should have high light extraction and heat dissipation efficiencies. For the flip-chip (FC) LEDs, the fabrication of high-performance p-type reflector with low contact resistance and high reflectivity is reqyired. Silver (Ag) is a commonly adopted p-type reflector for near UV LEDs but suffers from thermal instability, namely, agglomerated when annealed in air above 300 °C. In addition, electromigration (EM) is one of the major failure mechanisms of electronic interconnect under high current density (> ~105 A/cm2) stressing in microelectronics devices. In this talk, we investigated the opto-electrical properties, and electromigration reliability of a Ag-Pd-Cu alloy (APC) reflector for near UV (385 nm)-LEDs as a function of temperature and compared with those of Ag only reflector. SEM results revealed that the Ag samples were less stable than the APC samples upon annealing. The contact resistivities of the Ag and APC contacts annealed at 500 °C were measured to be 2.59 × 10– 4 and 1.85 × 10–4 Wcm2, respectively. The Ga 2p core level for the APC sample shifted towards the lower binding-energies by 0.67 eV as compared to that of the as-deposited sample. The forward I-V properties of near UV LEDs fabricated with the Ag and APC reflectors were observe to be similar each other. Notably, the UV LEDs with the APC reflector produced 9.04% higher output at 100 mA than those with the Ag reflector. To investigate the device reliability, the EM behaviour of Ag and APC films were also characterised. The APC samples exhibited better EM resistance than the Ag samples. The APC samples yielded higher activation energies of the EM failures than the Ag sample. The better EM behaviour of the APC samples will be described and discussed on the basis of XRD pole figure and electron back scatter diffraction, phi scan, and inverse pole figures (IPFs) examination results.

Effect of Microstructure and Texture Evolution During Variable Gauge Rolling on Mechanical Properties of Tailor Rolled Blanks

In this study, anisotropic elastic and plastic mechanical properties of a tailor rolled blank (TRB) with thickness ratio of 0.52 (1 mm/1.9 mm), have been fully studied. To gain a deeper insight into anisotropic mechanical behavior of the studied TRB, continuous changes in microstructure and crystallographic texture of a dual phase steel caused by variable gauge rolling (VGR) were investigated on several points (on RD–ND plane) along longitudinal direction with the aid of EBSD observations. Analysis of grain boundary (GB) maps revealed that ferrite grain refinement is occurred during VGR so that the average ferrite grain size decreases from 4.1 µm for the thicker side to 2.2 µm for the thinner side. Furthermore, it was found out that substructure density is more intense within smaller ferrite grains. Evaluation of inverse pole figures as well as orientation distribution function maps showed that texture of thicker side comprises {001}〈110〉 and {112}〈110〉 components along $$ \alpha $$ -fiber. In addition, it was revealed that orientations of {111}〈110〉 and {111}〈112〉 along $$ \gamma $$ -fiber strengthen along VGR direction by further increase in thickness reduction near thinner side. Accordingly, unprecedented gradual changes in mechanical properties with respect to these changes in microstructure and texture, were obtained. Finally, the correlation between in-plane anisotropic mechanical properties [Young’s modulus (E), yield stress (YS), ultimate tensile stress (UTS) and total elongation] of the studied tailor rolled blank with microstructure and deformation texture was interpreted.

Effect of crystallographic orientations on the corrosion resistance of Fe-17Cr ferritic stainless steel

Effect of crystallographic orientations on the corrosion resistance of the Fe-17Cr ferritic stainless steel sheets was investigated by electron backscatter diffraction and electrochemical measurements. Nearly homogeneous {111}〈112〉 γ-fiber recrystallization texture is produced in the Fe-17Cr ferritic stainless steel sheets. Comparison between the inverse pole figure orientation map and scanning electron microscopy microstructures etched by aqua regia reveals that the severest corrosion occurs on the sheet rolling surface where {111} crystal plane dominates. Electrochemical measurements demonstrate that the plane perpendicular to transverse direction displays the lowest corrosion current density. This indicates that this plane, where {110} plane dominates, exhibits the best corrosion resistance.

Influence of the Crystallographic Orientation on the Yield Strength and Deformation Mechanisms of Austenitic Grains in Metastable Stainless Steels Investigated by Spherical Nanoindentation

The mechanical behavior of a metastable stainless steel is studied by spherical nanoindentation, as a function of crystallographic orientation of its austenitic grains. The residual imprints are analyzed by electron backscattered diffraction (inverse pole figure, phase and geometrically necessary dislocation maps) and atomic force microscopy. Results showed that austenite grains with the most common crystallographic orientations display similar elasto‐to‐plastic transition, being the dislocation activity by the Frank‐Read source the main deformation mechanism. However, the amount of dislocations generated during indentation testing strongly depends on the crystallographic orientation. No evidence of stress‐induced phase transformation is observed.

Microstructure development of molybdenum during rotary friction welding

Rotary friction welding is a solid state welding process where the required heat for welding is generated by friction caused by the relative movement between a stationary part and its rotary counterpart. As the melting temperature is not reached, this welding technique does not produce typical welding defects known from fusion welding. In the case of molybdenum, grain coarsening and re-distribution of impurities on grain boundaries are the main problems during fusion welding that can partly be avoided by rotary friction welding.Pure molybdenum and the precipitation strengthened alloy TZM (titanium-zirconium-molybdenum) were subjected to rotary friction welding and a systematic parameter optimization led to successful welds. However, Mo and TZM proved to be very sensitive to small process parameter changes.Microstructural analysis shows a transition from elongated grains with intense substructure in the base material to nearly equiaxed grains at the weld interface is observed. Typical macroscopic zones in the joint can be distinguished and are investigated by electron backscatter diffraction (EBSD). Inverse pole figures maps, grain reference average misorientation maps and resulting grain sizes as well as orientation distribution functions (ODF) are considered to investigate the deformation state of the different zones.Continuous dynamic recrystallization and the competing dynamic recovery were observed as key mechanisms; Intensive subgrain formation and the onset of recrystallization played the major role on the microstructure modification due to rotary friction welding. Grain refinement is observed in the weld interface for the TZM, while coarse grains are observed in the same zone for the pure Mo but comparable crystallographic texture is observed for both materials.

Analytical calculation of saturated strain near morphotropic phase boundary of polycrystalline ferroelectrics by the generalized inverse-pole-figure model

The generalized inverse-pole-figure (IPF) model has been applied to analyze the saturated strain in polycrystalline ferroelectrics including composition near morphotropic phase boundary (MPB). Saturated strains of single-phase polycrystalline ferroelectrics with tetragonal and rhombohedral symmetry have been analytically calculated and the results have been confirmed by comparison with the results from preceding studies. In addition, the general formula to analyze relative saturated strain near MPBs of different multiple-phase polycrystalline ferroelectrics has been derived and the saturated strain near tetragonal-rhombohedral MPB has been calculated.

Investigation of Ferroelectric Grain Sizes and Orientations in Pt/CaxSr1⁻xBi₂Ta₂O₉/Hf⁻Al⁻O/Si High Performance Ferroelectric-Gate Field-Effect-Transistors.

Electron backscatter diffraction (EBSD) was applied to investigate the grain size and orientation of polycrystalline CaxSr1–xBi2Ta2O9 (CxS1–xBT) films in ferroelectric-gate field-effect transistors (FeFETs). The CxS1–xBT FeFETs with x = 0, 0.1, 0.2, 0.5, and 1 were characterized by the EBSD inverse pole figure map. The maps of x = 0, 0.1, and 0.2 showed more uniform and smaller grains with more inclusion of the a-axis component along the film normal than the maps of x = 0.5 and 1. Since spontaneous polarization of CxS1–xBT is expected to exist along the a-axis, inclusion of the film normal a-axis component is necessary to obtain polarization versus electric field (P–E) hysteresis curves of the CxS1–xBT when the E is applied across the film. Since memory windows of FeFETs originate from P–E hysteresis curves, the EBSD results were consistent with the electrical performance of the FeFETs, where the FeFETs with x = 0, 0.1, and 0.2 had wider memory windows than those with x = 0.5 and 1. The influence of annealing temperature for C0.1S0.9BT poly-crystallization was also investigated using the EBSD method.

On Structural Aspects of Texture Changes During Rolling of Zr-2.5%Nb Alloy

Using X-ray structural analysis, features of changes in characteristics of crystallographic texture during cold working of Zr-2.5%Nb alloy plates by longitudinal and cross rolling has been investigated. To make original plates, longitudinal fragments and rings of Æ15.0´1.5 mm² tube annealed at 580 °C were used. The plates were rolled at room temperature to the degrees in the range from 6 to 56% with 5…7% per pass and the rate of 5...10s-1. Using the method of inverse pole figures with measuring by the Bragg-Brentano optical scheme, densities of reflections along normal to plane of the plates (pole densities) was determined. Based on this, distributions of orientations of c-axes of hcp lattice of the material have been analyzed. Local features of the distributions, which were attributed to signs of twinning effects in texture changes in the alloy, are revealed. At subsequent analysis, an effect of strain non-uniformity associated with prehistory of the plates was taken into account. It is established that the second stage of (moderate) changes in Kearns textural coefficient of the plates with the deformation degrees differs from the initial stage of accelerated changes by activation of compression twins. By the method of tilt scanning (of rocking curves) around the Bragg-Brentano position at registration of (0004) reflection intensities, changes in orientation distributions of c-axes in longitudinal and cross section of the plates for both parties were investigated. It is noted that the main textural changes in process of deformation of the plates occur in the cross-sectional plane of the original tube and are most expressed on the cross-rolling plates. The doublet in the distributions of c‑axes, characteristic for rolling texture of hcp metals of titanium subgroup, was noted just at the second stage of the texture changes in the material. Its directionality is mainly associated with the plane of cross-section of the original tube. A connection is revealed between features of the pole density distributions and expression degree of the textural doublet on the rocking curves. According to the results obtained and analysis of other publications, twinning nature of the textural doublet was confirmed and a schematic sequence of its formation was proposed with participation of compression twins of{112-2}{1-1-23} system and tensile twins of {101-2}{1-011} and{112-1}{1-1-26} systems.

Regularities of Changes in Kearns Texture Coefficient at Cold Rolling of Zr-2.5%Nb Alloy

-ray studies of the changes in characteristics of crystallographic texture with cold deformation of Zr‑2.5%Nb alloy plates by longitudinal and cross rolling up to 56% at the speed of 5…10 sec-1 were carried out. The original plates were made from longitudinal fragments and rings cut from Æ15.0´1.5 mm² tube, and were then annealed at 580 °C. Texture of the plates was studied by the method of inverse pole figures with calculation of the Kearns texture coefficient along the normal to the plate plane. Dependences of the texture coefficient on degrees of deformation of the plates are built. A discrepancy was found between texture coefficient values measured on different sides of the plates, which is associated with the straightening of the original tube fragments and invariance of “c”-axes distribution after subsequent annealing of the initial plates. By introducing corrections to the degree of deformation calculated from the parameters of the cross section of the original tube, such discrepancies were eliminated for the data on cross-rolling of the material. As a result, for both deformation schemes, two stages of changes in the texture coefficient with alloy deformation were revealed: the initial stage of its growth and the subsequent stage of minor changes. Both stages are mainly linear and have the boundary value of the texture coefficient equal to 0.65...0.68. To study the structural mechanisms of changes in the texture of the alloy, an original technique of comparative analysis of changes in the texture coefficient of the material and in the distribution of crystallographic orientations is applied. It is established that at the initial stage of changes in the texture coefficient with deformation in both schemes, the rotation of the crystallographic “c” axes of the material occurs abruptly, and it does at angles of more than 60°. This confirms the essential role of twinning in the texture changes of the alloy. In particular, we have shown that the initial stage is significantly dominated by the {102}á011ñ system of tensile twins. Connection of twinning with differences in texture changes at the longitudinal and cross rolling of the alloy is discussed.

Notched Creep Damage Assessment Based on EBSD Observation for Austenitic Stainless Steel

Creep damage processes for smooth and notched specimen of austenitic stainless steel through interrupted creep tests using multiple specimens. The material used was 18-8 stainless steel for boiler tube use. The mid-sections of interrupted creep test specimens were observed through SEM(Scanning Electron Microscope) instrumented with EBSD(Electron BackScatter Diffraction patter) equipment. IPF(Inverse Pole Figure) maps, Phase maps and GOS(Grain Orientation Spread) maps were used for investigating creep damage process. For smooth specimen, the relationship between macroscopic creep time fraction and GOS averaged for all pixels showed linearity, while the relationship between creep strain and the averaged GOS showed non-linearity regressed by Green function successfully. For notched specimen, the EBSD maps became noisy possibly due to extensive phase transformation under highly concentrated notch stress. Obtained GOS data for gamma phase only showed non-monotonic change with time and nominal strain. The evaluated local strains in the vicinity of the notch showed relatively small amount, which might cause the very long creep life compared with smooth specimen under the same nominal stress condition.

Deformation Structures in a Duplex Stainless Steel

The evolution of the deformation structure with strain has been studied using electron backscatter diffraction (EBSD). Samples from interrupted uniaxial tensile tests and from a cyclic tension/compression test were investigated. The evolution of low angle boundaries (LABs) was studied using boundary maps and by measuring the LAB density. From calculations of local misorientations, smaller orientation changes in the substructure can be illustrated. The different orientations developed with strain within a grain, due to operation of different slip systems in different parts of the grain, were studied using a misorientation profile showing substantial orientation changes after a true strain of 0.24. The texture evolution with increasing strain was followed by using inverse pole figures (IPFs). The observed substructure development in the ferritic and austenitic phases could be successfully correlated with the stress-strain curve from a tensile test. LABs were first observed in the different phases when the strain hardening rate changed in appearance indicating that cross slip started to operate as a significant dislocation recovery mechanism. The evolution of the deformation structure is concluded to occur in a similar manner in the austenitic and ferritic phases but with different texture evolution for the two phases.