Crystallographic Misorientation Research Articles

Local thermal conductivity of polycrystalline AlN ceramics measured by scanning thermal microscopy and complementary scanning electron microscopy techniques

The local thermal conductivity of polycrystalline aluminum nitride (AlN) ceramics is measured and imaged by using a scanning thermal microscope (SThM) and complementary scanning electron microscope (SEM) based techniques at room temperature. The quantitative thermal conductivity for the AlN sample is gained by using a SThM with a spatial resolution of sub-micrometer scale through using the 3ω method. A thermal conductivity of 308 W/m·K within grains corresponding to that of high-purity single crystal AlN is obtained. The slight differences in thermal conduction between the adjacent grains are found to result from crystallographic misorientations, as demonstrated in the electron backscattered diffraction. A much lower thermal conductivity at the grain boundary is due to impurities and defects enriched in these sites, as indicated by energy dispersive X-ray spectroscopy.

Inclusion-localised crystal-plasticity, dynamic porosity, and fast-diffusion pathway generation in zircon

A population of oscillatory zoned, igneous zircon grains in a Javanese andesite contains fluid and mineral inclusions (up to 10 μm across) trapped during zircon growth. Orientation contrast imaging and orientation mapping by electron backscatter diffraction reveal that crystal-plastic deformation overprints growth zoning and has localized around 1–10 μm pores and inclusions. Cumulative crystallographic misorientation of up to 25° around pores and inclusions in zircon is predominantly accommodated by low-angle (<5°) orientation boundaries, with few free dislocations in subgrain interiors. Low-angle boundaries are curved, with multiple orientation segments at the sub-micrometer scale. Misorientation axes associated with the most common boundaries align with the zircon c-axis and are consistent with dislocation creep dominated by <100>(010) slip. A distinctly different population of sub-micron pores is present along subgrain boundaries and their triple junctions. These are interpreted to have formed as a geometric consequence of dislocation interaction during crystal-plasticity. Dislocation creep microstructures are spatially related to differences in cathodoluminescence spectra that indicate variations in the abundance of CL-active rare earth elements. The extent of the modification suggests deformation-related fast-pathway diffusion distances that are over five orders of magnitude greater than expected for volume diffusion. This enhanced diffusion is interpreted to represent a combination of fast-diffusion pathways associated with creep cavitation, dislocations and along low-angle boundaries. These new data indicate that ductile deformation localised around inclusions can provide fast pathways for geochemical exchange. These pathways may provide links to the zircon grain boundary, thus negating the widely held assumption that inclusions in fracture-free zircon are geochemically armoured once they are physically enclosed.

Crack–grain boundary interactions in zinc bicrystals

In polycrystalline materials that fail by transgranular cleavage, it is known that crystallographic misorientation of preferred fracture planes across grain boundaries can provide crack growth resistance; despite this, the micromechanisms associated with crack transmission across grain boundaries and their role in determining the overall fracture resistance are not well understood. Recent studies on diverse structural materials such as steels, aluminum alloys and intermetallics have shown a correlation between fracture resistance and the twist component of grain misorientation. However, the lack of control over the degree and type of misorientation in experimental studies, combined with a dearth of analytical and computational investigations that fully account for the three-dimensional nature of the problem, have precluded a systematic analysis of this phenomenon. In this study, this phenomenon was investigated through in situ crack propagation experiments across grain boundaries of controlled twist misorientation in zinc bicrystals. Extrinsic toughening mechanisms that activate upon crack stagnation at the grain boundary deter further crack propagation. The mechanical response and crack growth behavior were observed to be dependent on the twist angle, and several accommodation mechanisms such as twinning, strain localization and slip band blocking contribute to fracture resistance by competing with crack propagation. Three-dimensional finite element analyses incorporating crystal plasticity were performed on a stagnant crack at the grain boundary that provide insight into crack-tip stress and strain fields in the second grain. These analyses qualitatively capture the overall trends in mechanical response as well as strain localization around stagnant crack-tips.

Effect of microstructure on the nucleation of deformation twins in polycrystalline high-purity magnesium: A multi-scale modeling study

A multi-scale, theoretical study of twin nucleation from grain boundaries in polycrystalline hexagonal close packed (hcp) metals is presented. A key element in the model is a probability theory for the nucleation of deformation twins based on the idea that twins originate from a statistical distribution of defects in the grain boundaries and are activated by local stresses at the grain boundaries. In this work, this theory is integrated into a crystal plasticity constitutive model in order to study the influence of these statistical effects on the microstructural evolution of the polycrystal, such as texture and twin volume fraction. Recently, a statistical analysis of exceptionally large data sets of {101̄2} deformation twins was conducted for high-purity Mg ( Beyerlein et al., 2010a). To demonstrate the significantly enhanced accuracy of the present model over those employing more conventional, deterministic approaches to twin activation, the model is applied to the case of {101̄2} twinning in Mg to quantitatively interpret the many statistical features reported for these twins (e.g., variant selection, thickness, numbers per grain) and their relationship to crystallographic grain orientation, grain size, and grain boundary misorientation angle. Notably the model explains the weak relationship observed between crystal orientation and twin variant selection and the strong correlation found between grain size and the number of twins formed per grain. The predictions suggest that stress fluctuations generated at grain boundaries are responsible for experimentally observed dispersions in twin variant selection.

Distinguishing crystallographic misorientations of lanthanum zirconate epilayers on nickel substrates by electron backscatter diffraction

Electron backscatter diffraction (EBSD) was used for distinguishing crystallographic orientations and local lattice misfits of a La 2Zr 2O 7 (LZO) buffer layer epitaxially grown on a cube textured Ni-5.%W (Ni–W) substrate for a YBCO superconductor film. Orientation data were obtained from the LZO epilayer using low energy primary electrons (5 keV) and from the Ni–W substrate by increasing the voltage to 15 keV. In-plane and out-of-plane orientations of the LZO epilayer were revealed with respect to its Ni–W substrate. A strong {1 0 0} 〈0 1 1〉 rotated-cube texture in the LZO epilayer was formed on the {1 0 0} 〈0 0 1〉 cube-textured Ni–W substrates. LZO and Ni in-plane crystallographic axes are related by an expected 45° rotation. The step-misorientations and the local misfit strains between the LZO epilayer and the substrate were also analyzed.

Proposition of a Crystal Plasticity Constitutive Equation Based on Crystallographic Misorientation Theory

In this study, we try to reveal the relationship between the plastic deformation and the microscopic crystal misorientation evolution by using the homogenized finite element (FE) procedure with the proposed crystal plasticity constitutive equation. Since plastic deformation of polycrystal sheet metal is greatly affected by its initial and plastic deformed textures, multi-scale FE analysis based on homogenization theory with considering micro polycrystal morphology is required. We formulated a new crystal plasticity constitutive equation to introduce not only the effect of crystal orientation distribution, but also the size of crystal grain and/or the effect of crystal grain boundary for the micro FE analysis. The hardening evolution equation based on strain gradient theory was modified to consider curvature of crystal orientation by using crystallographic misorientation theory. We employed two-scale structure, such as a microscopic polycrystal structure and a macroscopic elastic/plastic continuum. Our analysis code predicts the plastic deformation of polycrystal metal in macro-scale, and simultaneously crystal texture and misorientation evolutions in the micro-scale. The crystallographic misorientation evolution induced by the plastic deformation of polycrystal aluminum alloy was investigated by using the multi-scale FE analysis with new proposed hardening evolution equation. We confirmed the availability of our analysis code employing the new constitutive equation through the comparison with numerical and experimental results of uniaxial tensile problem.

GRENVILLE SKARN TITANITE: POTENTIAL REFERENCE MATERIAL FOR SIMS U-Th-Pb ANALYSIS

We have investigated the homogeneity, chemical composition, structure, degree of radiation damage, and post-formation evolution of titanite crystals from skarns of the Grenville Province of the Canadian Shield using SHRIMP, TIMS, Raman and PL spectroscopy, EBSD, and EPMA–WDS. These results are used to assess the potential of the titanite as Reference Material (RM) for micro-analytical U–Th–Pb age dating. The SHRIMP data show that these megacrysts (5–31g) have concordant U–Pb isotope systematics, 60 to 500 ppm U, 120 to 1200 ppm Th, 206 Pb/ 204 Pb between 500 and 2500, ages of ~1 Ga, and excellent homogeneity at the scale of the analytical volume of the ion probe. The ID–TIMS titanite data for OLT1, OLT2 and TCB show that these crystals are essentially concordant. Data for OLT1 and OLT2 show slight scatter ( i.e. , in excess of that expected from the uncertainty in an individual analysis). For OLT1, one of seven analyses shows Pb loss or, possibly, a younger period of growth. Crystals OLT1 and OLT2 have respective TIMS concordia ages of 1014.8 ± 2.0 Ma (2σ, n = 6, MSWD = 1.8) and 998.0 ± 4.5 Ma (2σ, n = 3, MSWD = 3.3) for domains that have not lost Pb. The TIMS analyses of TCB are tightly clustered and give a concordia age of 1018.1 ± 1.7 Ma (2σ, n = 4, MSWD = 0.92). Raman and PL spectra show a low to moderate degree of accumulated radiation-induced damage in the Grenville Skarn Titanite crystals and uniform internal distributions of this damage. The EDSB contrast images indicate little or no crystallographic misorientation. The EMPA–WDS data show that the outer 50–100 μm of the OLT1 and TCB crystals are enriched in Al and F, and depleted in Fe and Nb, when compared with the interior. In spite of the variation in composition and degree of radiation damage amongst samples, there are no identifiable matrix effects in our SHRIMP data. Some Grenville skarn titanite (GST) crystals have potential as RM for micro-analytical U–Th–Pb age dating. Crystal TCB has excellent homogeneity of U–Th–Pb isotopic composition. Crystals OLT1 and OLT2 have minor TIMS age heterogeneity. However, this heterogeneity is smaller than that of the Khan titanite, our current in-house titanite standard. Careful selection of analysis areas during SIMS, and of chips for TIMS analysis, allows high-quality isotopic data to be obtained from these large crystals of titanite.

Relationship among titanium, rare earth elements, U–Pb ages and deformation microstructures in zircon: Implications for Ti-in-zircon thermometry

A zircon grain in an orthopyroxene–garnet–phlogopite–zircon–rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal–plastic deformation. The zircon grain records significant variations in titanium (Ti) from 2.6 to 30 ppm that corresponds to a difference in calculated Ti-in-zircon temperatures of over several hundred degrees Celsius. The highest Ti concentration is measured at subgrain centres (30 ppm), and Ti is variably depleted at low-angle boundaries (down to 2.6 ppm). Variations in cathodoluminescence coincide with the deformation microstructure and indicate localised, differential enrichment of rare earth elements (REE) at low-angle boundaries. Variable enrichment of U and Th and systematic increase of Th/U from 1.61 to 3.52 occurs at low-angle boundaries. Individual SHRIMP-derived U–Pb ages from more deformed zones (mean age of 1799 ± 40, n = 22) are systematically younger than subgrain cores (mean age of 1851 ± 65 Ma, n = 7), and indicate that open system behaviour of Ti–Th–U occurred shortly after zircon growth, prior to the accumulation of significant radiogenic Pb. Modelling of trace-element diffusion distances for geologically reasonable thermal histories indicates that the observed variations are ~ 5 orders of magnitude greater than can be accounted for by volume diffusion. The data are best explained by enhanced diffusion of U, Th and Ti along deformation-related fast-diffusion pathways, such as dislocations and low-angle (< 5°) boundaries. These results indicate chemical exchange between zircon and the surrounding matrix and show that Ti-in-zircon thermometry and U–Pb geochronology from deformed zircon may not yield information relating to the conditions and timing of primary crystallisation.

Texture evolution and grain refinement of ultrafine-grained copper during micro-extrusion

Samples of oxygen-free high conductivity (OFHC) coarse-grained (CG) and ultrafine-grained (UFG) copper were micro-extruded to an equivalent strain of 2.8 in one pass at room temperature. Samples of the OFHC copper were annealed at 650°C for 2 h to produce CG copper. Some samples were subsequently processed by equal channel angular pressing of eight passes, route Bc, at room temperature to produce the UFG material. Crystallographic texture and misorientation distributions were obtained locally from EBSD mappings at different radial positions after micro-extrusion. To model the strain path during micro-extrusion, the analytic flow line model of Altan et al. [J Mater. Process. Tech. 33 (1992) p.263] was used and also validated by finite element calculations. Modelling was carried out using the viscoplastic self-consistent (VPSC) model and a recently developed grain refinement model. The results showed large texture variations along the cross-section of the extruded sample for both UFG and CG copper. These cyclic drawing textures in UFG copper were simulated in good agreement with experiments using the presented modelling framework.

Dissolution–reprecipitation of igneous zircon in mid-ocean ridge gabbro, Atlantis Bank, Southwest Indian Ridge

Zircons recovered from oceanic gabbro exposed on Atlantis Bank, Southwest Indian Ridge, typically display oscillatory and sector zoning consistent with igneous crystallization from mafic magmas. In one rock (of twenty investigated), weak-oscillatory-zonation patterns are overprinted by secondary textural features characterized by mottled, convoluted and wavy internal zonation patterns that are frequently associated with secondary micron- to submicron-scale micro-porosity. These zircons are hosted in a felsic vein that intruded an oxide gabbro, both of which are cross-cut by monomineralic amphibole- and quartz-rich veinlets. Zircons with weak-oscillatory-zonation patterns record a weighted-average 206Pb/ 238U age of 12.76 ± 0.20 Ma (mswd = 1.5), and have high trace element concentrations [e.g., ΣREEs (∼ 0.4–2.2 wt.%), Y (∼ 0.6–2.8 wt.%), P (∼ 0.4–0.9 wt.%)], and Th/U (0.1–0.5). These zircons are anomalously old (≥1 Myr) relative to the magnetic age for this portion of oceanic crust (11.75 Ma). In contrast, zircons with non-igneous, secondary textures have a younger weighted-average 206Pb/ 238U age of 12.00 ± 0.16 Ma (mswd = 1.7), and have lower trace element concentrations [e.g., ΣREEs (∼ 0.2–0.8 wt.%), Y (∼ 0.3–1.0 wt.%), P (∼ 0.1–0.3 wt.%)], and slightly lower Th/U (0.1–0.3). The weighted-average age of these zircons is similar to the magnetic anomaly age, and other 206Pb/ 238U ages of nearby rocks. We do not observe a correlation between crystallographic misorientation, internal texture, or trace element chemistry. We suggest that the decrease in trace element concentrations associated with the development of non-igneous alteration textures is attributed to the purging of non-essential structural constituent cations from the zircon crystal lattice at amphibolite-facies conditions. The mechanism of alteration/re-equilibration was likely an interface-coupled dissolution–reprecipitation processes that affected pre-existing, anomalously old zircons during shallow-level magmatic construction of Atlantis Bank at ∼ 12.0 Ma.

Multilevel modular mesocrystalline organization in red coral

Biominerals can achieve complex shapes as aggregates of crystalline building blocks. In the red coral skeleton, we observe that these building blocks are arranged into eight hierarchical levels of similarly (but not identically) oriented modules. The modules in each hierarchical level assemble into larger units that comprise the next higher level of the hierarchy, and consist themselves of smaller, oriented modules. EBSD and TEM studies show that the degree of crystallographic misorientation between the building blocks decreases with decreasing module size. We observe this organization down to a few nanometers. Thus, the transition from imperfect crystallographic order at millimeter scale to nearly perfect single crystalline domains at nanometer scale is progressive. The concept of mesocrystal involves the three-dimensional crystallographic organization of nanoparticles into a highly ordered mesostructure. We add to this concept the notion of modularity. This modularity has potential implications for the origin of complex biomineral shapes in nature. A multilevel modular organization with small intermodular misorientations combines a simple construction scheme, ruled by crystallographic laws, with the possibility of complex shapes. If the observations we have made on red coral extend to other biominerals, long-range crystallographic order and interfaces at all scales may be key to how some biominerals achieve complex shapes adapted to the environment in which they grow.

Development of novel grain morphology during hot extrusion of magnesium AZ21 alloy

Microstructure and microtexture evolution during static annealing of a hot-extruded AZ21 magnesium alloy was studied. Apart from fine recrystallized equiaxed grains and large elongated deformed grains, a new third kind of abnormal grains that are stacked one after the other in a row parallel to the extrusion direction were observed. The crystallographic misorientation inside these grains was similar to that of the fine recrystallized grains. The large elongated grains exhibited significant in-grain misorientation. A self-consistent mechanistic model was developed to describe the formation of these grain morphologies during dynamic recrystallization (DRX). The texture of pre-extruded material, although lost in DRX, leaves a unique signature which manifests itself in the form of these grain morphologies. The origin of abnormal stacked grains was associated with slow nucleation in pre-extruded grains of a certain orientation. Further annealing resulted in large secondary recrystallized grains with occasional extension twins.

Caracterización mediante la técnica EBSD de la deformación de chapa de acero inoxidable AISI 304 DDQ bajo tensiones multiaxiales típicas de la embutición

The main aim of this work is to evaluate AISI 304 DDQ stainless steel behaviour under deep drawing deformation condition, that is, pure shear deformation in which material suffers a typical deformation under tension-biaxial compression stresses system. The microestructural evolution has been investigated by optical microscopy and by EBSD technique. The success of the EBSD analysis has been established for the deformation conditions experimented here. It has been determined the rolling direction and the equivalent strain influence on the crystallographic orientation maps, misorientation diagrams and poles figures. The results let the authors say the low angle misorientations corresponding to 0, 45 and 90° rolling directions have an inverse correlation with the material anisotropy. Initial prestraining has been considered also and the analysis of this aspects lead to establish that the increment of the intragranular misorientations with the strain depends on the initial state of the steel; this increment is observed to be minor for samples with initial prestraining. High angle misorientation analysis (>15°) indicates that the grain boundaries character distributions depends on the deformation.

Fragmentation in an Al–7 wt-%Si alloy studied in real time by X-ray synchrotron techniques

One mechanism for the formation of equiaxed grains is the detachment of dendrite fragments which is believed to be at the origin of the central equiaxed core region in casting processes. Unfortunately, the dynamics of the fragmentation phenomena cannot be revealed by classical methods. Investigation of a unrefined Al–7 wt-%Si alloy using in situ and real time synchrotron X-radiography and X-ray topography at the European Synchrotron Radiation Facility, has allowed verification of the existence of dendrite fragmentation and of cascade fragmentation during directional solidification, and to study the evolution of the growth and sedimentation of the equiaxed grains formed from these fragments. An examination of the crystallographic misorientation of dendrites as fragmentation is ongoing. These results contribute to the understanding of the characteristics of the columnar to equiaxed transition and to knowledge of the origin of new equiaxed grains in unrefined alloys.

Study on the growth behavior of voids located at the grain boundary

The growth behavior of voids located at the grain boundary was numerically simulated with three dimensional crystal plasticity finite element model, which was implemented with the rate-dependent crystal plasticity theory code as user material subroutine. A three dimensional (3D) bicrystal model was created to simulate the growth behavior of voids located at the grain boundary and the plastic deformation distribution around the voids, and the effects of crystallographic orientation and the angle θ of the grain boundary direction with respect to the tensile axis on fracture mode were analyzed. Under uniaxial tension condition, the unit cell with θ = 0° tends to fail by transgranular fracture, and the unit cell with θ = 45° is more likely to fail by intergranular fracture. With the orientation factor’s difference between the two grains increasing, larger heterogeneous deformation may occur between the two grains, which leads to large equivalent plastic deformation along the grain boundary, and the unit cell tends to fail by intergranular fracture. Under triaxial tension condition, the void with a spherical initial shape develops an irregular shape, and sharp corners started from the internal surface of the void are induced along the grain boundary. Results show that the maximal plastic deformation at the corners is related to the crystallographic orientation and misorientation.

The role of crystal misorientations during solid-state nucleation of ferrite in austenite

The role of grain and phase boundary misorientations during nucleation of ferrite in austenite has been investigated. Electron back-scatter diffraction (EBSD) was performed on a high-purity iron alloy with 20 wt.% Cr and 12 wt.% Ni with austenite and ferrite stable at room temperature in order to identify the crystallographic misorientation between austenite grains and between ferrite and austenite grains. It is observed that the specific orientation relationships between ferrite and austenite play a dominant role during solid-state nucleation of ferrite. Ferrite grains nucleate on grain faces independently of the misorientation between austenite grains, although random high-angle grain boundaries have a slightly higher efficiency. Different types of nucleation mechanisms are found to be active during ferrite formation at grain faces. A slight deformation of the austenite matrix was found to triple the number of ferrite nuclei during isothermal annealing.

Yield-Point Phenomena of Ti-20V-4Al-1Sn at 1073 K and Its Constitutive Modelling

The deformation behaviour of β titanium alloy Ti-20V-4A1-1Sn sheet at 1073K was investigated by performing uniaxial tension experiments. The stress-strain curves show a sharp yield point and the subsequent abrupt yield drop followed by the strain softening. From the EBSD analysis, a crystallographic misorientation was found in grains even at an early stage of yielding, even though the dynamic recovery had not yet taken place. To describe such a characteristic stress-strain response, a viscoplastic constitutive model is proposed that is built on the premise that the yield point phenomena are associated with the rapid dislocation multiplication at an early stage of yielding.

Spatially Resolved X-ray Diffraction Technique for Crystallographic Quality Inspection of Semiconductor Microstructures

There is an increasing demand for techniques that allow detection and visualization of crystalline lattice microdefects. From the many techniques available the X-ray Rocking Curve Imaging (RCI), based on synchrotron X-ray diffraction, has gained much attention recently as a method of wafer defect analysis [1]. However, for most crystal growers laboratory techniques are preferred. Therefore, instead of applying RCI we have developed a microimaging technique based on spatially resolved X-ray diffraction (SRXRD) that makes use of conventional high resolution X-ray diffractometer. Briefly, the size of incident X-ray beam is reduced by a set of slits. Then the sample is moved in small steps while the rest of the system stays fixed. At each sample position X-ray diffraction curve is measured from precisely defined area. Finally, all diffraction curves are collected to construct the X-ray diffraction image of the sample. Both the ω and 2θ/ω scans are performed allowing independent mapping of crystallographic misorientation and lattice parameter distributions across the sample. Spatial resolution offered by the SRXRD technique is smaller than that obtainable with the use of synchrotron radiation based methods. This is due to a limited radiation intensity of conventional X-ray sources. We have checked that in our experimental setup measurable signals can be obtained with the X-ray beam as small as 10/sinθ × 100 μm 2 , where θ is the Bragg angle for the reflection studied. This corresponds to the beam spot size of ~18 × 100 μm 2 for 004 reflections of GaAs and Si. The aim of this report is to present advantages of SRXRD over a standard X-ray diffraction when applied for analysis of crystalline microstructures. First, we focus on SRXRD studies of epitaxial laterally overgrown (ELO) GaAs layers grown by liquid phase epitaxy on SiO2-masked GaAs substrates. ELO layer consists of a few hundreds micrometers wide monocrystalline stripes regularly arranged on a substrate. Since each stripe is strained such samples contain a periodic distribution of strain and/or defects. Thus, they are very suitable to demonstrate potential of the technique. We show that high spatial and angular resolutions of SRXRD allow studying a strong effect of ELO wings tilt towards the mask as well as very fine residual strain caused by dopant concentration inhomogeneity. Direction of the tilt and the distribution of tilt magnitude across width of each wing can be easily determined. In fully overgrown GaAs ELO layers additional strain was observed at a coalescence front where ELO wings grown from adjacent seeds merged. With the use of SRXRD a local structure of the crystal lattice around this coalescence front was studied. In heteroepitaxial GaSb/GaAs ELO layers local mosaicity in the wing area was found. By SRXRD the size of microblocks and their relative misorientation were analyzed. As the final example, we report on strain distribution in thermally oxidized Si wafers. Microscopic curvature of lattice planes confined between two neighboring slip bands was measured allowing its correlation with the dislocation structure. It is noting worthy that all the phenomena presented are difficult to study by standard X-ray diffraction. On the contrary, due to its high spatial resolution the SRXRD technique allows deeper insight into a localized strain fields present in semiconductor microstructures.

Microstructural evolution of Mg–Al–Ca–Sr alloy during creep

To provide new insight into microstructural development during creep, sequential EBSD (electron backscatter diffraction) orientation maps were obtained from fixed surface areas at intervals in creep tests of a high-pressure die-cast Mg–8.5Al–1Ca–0.3Sr alloy. Samples were tested at 200 °C at various stress levels to achieve power-law creep behavior. In all specimens, steady-state creep was marked by the formation of tension twins. At intermediate stress levels, specimen failure was initiated by the formation of defects at boundaries with high crystallographic misorientation. However, at high stress levels, the failure mechanism was assisted by the crack formation at interdendritic boundaries with low crystallographic misorientation.

Plastic Deformation Quantified by Atomic Force Microscopy Measurements for Duplex Stainless Steel under Monotonic and Cyclic Loading

By atomic force microscopy, the plastic deformation marks resulting from monotonic and cyclic plastic deformation were analysed to study the plasticity in each phase of Duplex Stainless Steels. In austenite, straight slip bands were observed after monotonic loading. These straight slip bands seem to serve as fatigue extrusion nucleation sites, which are the marks of the accommodation of the cyclic plasticity by the austenite. In ferrite, after monotonic loading, slip bands, could be classified into two different groups depending on whether they result from the bulk activities of ferrite or whether their formation is assisted by the plastic deformation of austenite. It was found that the crystallographic misorientation based on a Kurdjomov-Sachs relationship is the factor controlling one or the other type. After the first 5 loading cycles, the ferrite presents only monotonic plastic marks. This suggests no direct contribution of the ferrite to the accommodation of the cyclic plasticity.