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We investigated the flow behavior of γ/γʹ-strengthened Co-12Ti and Co-12Ti-4Mo (at.%) alloys at room and elevated temperatures (up to 900°C) by electron microscopy and density functional theory. The Mo-added alloy exhibited an enhanced compressive yield strength and strain hardening behavior as compared to the reference binary alloy. This behavior could be attributed to a ~25% larger γʹ volume fraction and ~7% higher planar fault energies in Co-12Ti-4Mo. Using electron channeling contrast imaging, we observed interrupted slip bands in the Co-12Ti-4Mo alloy deformed to a strain of 6%, which led to enhanced strain hardening, in contrast to extended slip bands along {111} planes in the Co-12Ti alloy. Interrupted slip band formation in Co-12Ti-4Mo could be explained by rapid exhaustion of dislocation sources and a higher energy barrier required to cut the γʹ precipitates. These effects are due to a reduced γ channel width and substantial hardening effect of γʹ-Co 3 (Ti,Mo) in the ternary alloy as well as due to the large shear modulus difference between γʹ and γ. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Shear strain profiles along slip bands in a modified Rolls-Royce nickel superalloy (RR1000) were analyzed for a tensile sample deformed by 2%. The strain increased with distance away from a grain boundary (GB), with maximum shear strain towards the center of the grain, indicating that dislocation nucleation generally occurred in the grain interior. The strain gradients in the neighborhood of the GBs were quantified and generally correlated with rotation about the active slip system line direction. This leads to an ability to determine the active slip system in these regions. The dislocation spacing and pileup stresses were inferred. The dislocation spacing closely follows an Eshelby analytical solution for a single ended pileup of dislocations under an applied stress. The distribution of pileup stress values for GBs of a given misorientation angle follows a log-normal distribution, with no correlation between the pileup stress and the GB misorientation angle. Furthermore, there is no observed correlation between various transmissivity factors and slip band pileup stress. Hence it appears that the obstacle strength of any of the observed GBs is adequate to facilitate the dislocation pileups present in the slip bands. However, slip band transmission does correlate with transmissivity factors, with the current study focusing on the Luster and Morris m'-factor. Observation of strain profiles of transmitted bands indicate dislocation nucleation locations. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Systematic study was conducted on the microstructures and mechanical properties of nickel samples with two distinct types of heterostructures. The first is featured with coarse-grained lamellae embedded in a matrix consisting of a very high density of dislocation structures. The second is featured with coarse-grained zones embedded in the ultrafine-grained matrix. The second type of heterostructures exhibits better strength and ductility, although it has a smaller average grain size than the first type. The zone boundaries in the second type of heterostructures are less prone to cracking than those in the first type. Intersecting micro-shear-bands formed net-like patterns in the second type of heterostructures during tensile deformation. This is the first ever observation of structural micro-shear-bands in a heterostructured material. It supports the claim that heterostructure promotes the formation of dispersive shear bands. In contrast, a macroscopic shear band formed and caused early failure of the sample with the first type of heterostructures. Our results indicate that well-developed ultrafine/nano grained matrix in heterostructured materials are necessary for preventing crack formation and shear band localization. This should be considered as a key factor for optimizing the mechanical properties of heterostructured materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Plastic deformation during low cycle fatigue in fcc materials with low stacking fault energy is accumulated in slip bands, which become preferential sites for crack initiation. Whilst these dislocation structures have been studied before, little has been done to assess the effect and evolution of the individual slip lines within them. In this study, samples of a γ ′ precipitate strengthened nickel-based superalloy are fatigued at room temperature and 700 ∘C for 1, 40 and 500 cycles. The resulting dislocation structures are characterised via Electron Channeling Contrast Imaging and Transmission Electron Microscopy. We introduce a new methodology to measure slip band parameters such as the slip line spacing and shear step length by analysing the holes left by sheared precipitates in γ ′-etched secondary electron micrographs. Statistics of these parameters are obtained and compared for different conditions. Advantages of this technique include resolution at the scale of individual planes, acquisition of true three-dimensional data and applicability in the bulk of the material. The combination of these techniques provides a unique mechanistic and quantitative insight into the slip band and precipitate morphology evolution. [ABSTRACT FROM AUTHOR]

• We perform atomistic simulations of deformation in Ni with He bubbles and SIA clusters. • Nanotwins form in a model with free surfaces, slip bands form in a model without free surfaces. • He bubbles deform severely within slip bands and nanotwins, but do not coalesce or form incipient cracks. This paper presents molecular dynamics (MD) simulations of plastic deformation in single-crystal Ni models containing internal distributions of helium (He) bubbles and self-interstitial atom (SIA) clusters corresponding to experimental characterization of ex-service Inconel X-750 components. We simulate single crystals with and without free surfaces at room temperature and 588K, the latter temperature corresponding to the Inconel X-750 service conditions. Both models are deformed under multiple slip to a maximum deviatoric strain of ∼10 %. A dislocation slip band forms in the model without free surfaces, but not in the model with free surfaces. However, the latter exhibits nano-twin nucleation from surfaces. Helium (He) bubbles that overlap with a slip band or a nano-twinned region deform more severely than other bubbles in the model. Nevertheless, the bubbles do not link up and do not form configurations that resemble incipient cracks. [ABSTRACT FROM AUTHOR]

The LCF behaviors of two Ni-based single-crystal superalloys at room temperature and 600 °C have been studied. Superalloy with 3 wt% Ru-containing (3Ru alloy) had more excellent fatigue performances than that of non-Ru superalloy (0Ru alloy). Microstructures observed by transmission electron microscope showed that 0Ru alloy exhibited slip bands with orthogonal slip directions after the test. (1ī1) [011] and (1ī1) [0ī1] slip systems were activated in plastic deformation process. While (111) [0ī1] and (1ī1) [0ī1] slip systems of 3Ru alloy were along the single slip direction. Therefore, adding alloying element Ru to the superalloy promoted uniform deformation and prolonged fatigue life. Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract The characteristics of slip band and its interplay with dynamic precipitation of α phase during the thermo–mechanical coupling process in titanium alloy is really interesting but is not sufficiently ascertain. In the present work, the formation of slip bands, dynamic microstructure evolution and crystallographic orientation relationship during warm deformation of Ti-5553 alloy were investigated using Scanning Electron Microscopy/Transmission Electron Microscopy/crystallographic calculations. Results reveal that multiple-slip bands with two or three different propagating directions would form during the warm compression. These three distinctly oriented bands could be estimated as slip bands of (112) [ 11 1 ¯ ] , (1 2 ¯ 3 ¯ ) [ 1 1 ¯ 1 ] and ( 2 ¯ 13) [ 1 1 ¯ 1 ] types. Nano/ultrafine-trimorphic structure (lamellar α, equiaxed α and irregular α) formed dynamically during the warm deformation process due to the dynamic interplay between the initiation of the slip bands and the nucleation of α phase. There is an obvious competitive mechanism between dynamic recovery/dynamic recrystallization and α phase nucleation, which depended on the deformation parameters and modes. These results could provide valuable reference for process optimization and the microstructural evolution controlling. Graphical abstract Image 1 Highlights • The multiple-slip bands were formed in Ti-5553 alloy during the warm deformation. • Slip systems were identified accurately via crystallographic and matrix calculations. • The hot deformation mechanisms of titanium alloys were systematically considered. • Nano/ultrafine-trimorphic structure can be successfully produced in Ti-5553. [ABSTRACT FROM AUTHOR]

Highlights • Analysis of circa 12,000 micrographs of Antarctic ice from 8 depths and covering the range 94–853 m revealed two contrasting evolution regimes for the orientation of slip bands. • Unexpected behavior of slip bands in shallow bubbly ice reveals the inheritance of certain mechanical and microstructural features from ancient firn, probably related to former force chains within the firn skeleton. • Such inherited features gradually fade away in shallow bubbly ice, through the action of dynamic recovery and recrystallization, and the redistribution of internal stresses. This evanescence is explained through the postulation of a new hypothesis of microstructural fading memory. • The hypothesis of microstructural fading memory is compatible with a number of observations of microstructure evolution in firn and ice, and it lays the foundations for a new experimental and theoretical framework to study the elusive process of dynamic recovery in polar ice. Abstract The Antarctic Ice Sheet is a continental ice mass with circa 23 million gigatons of ice, which represent roughly 67 % of world's freshwater supply. This colossal mass of ice is by no means static, as the old ice slowly creeps under its own weight towards the ocean, while new ice is continually formed through the sintering of snow deposited on the ice sheet surface. A crucial role in this metamorphism is played by firn, which is the porous material in an intermediate state between the granular snow and the solid polycrystalline ice. Understanding the snow–firn–ice metamorphism is essential not only for a precise determination of the mechanical (creep) properties of polar ice, but also for comprehending the formation and decay of climate proxies widely used in ice-core studies. This work investigates the transition from firn to ice through the spatial and directional distributions of slip bands in bubbly ice. The analysis of high-resolution micrographs of ice sections extracted from the EPICA-DML Deep Ice Core allows us to identify a clear influence of strain-induced anisotropy (viz. c -axis preferred orientations) on the evolution of slip-band inclinations in deep bubbly ice. In contrast, we discover an unanticipated behaviour of slip bands in shallow bubbly ice, which prompts the introduction of the hypothesis of microstructural fading memory and the definition of a stabilization zone that may penetrate hundreds of metres into the bubbly ice. Within this stabilization zone, highly localized concentrations of strain energy and internal stresses once generated by force chains in the ancient firn are gradually redistributed by the newly formed bubbly-ice microstructure. We show that this hypothesis is compatible with the localized dynamic recrystallization episodes observed in polar firn (even at temperatures close to − 45 ∘ C), and it may also explain the sluggish rotation of c -axes observed in the upper hundreds of metres of polar ice sheets. [ABSTRACT FROM AUTHOR]

• Novel technique for visualizing laser-induced strain/slip generation. • Effects of crystallographic orientation with respect to laser trajectory. • Effects of process parameters and extent of melting on resulting slip characteristics. • Establishes basis for validation of crystal plasticity modelling of full thermo-elastoplastic process. The capability to characterize the inelastic response of a material induced by laser processing is particularly relevant within the context of laser-based additive manufacturing. While many efforts have been directed toward elastic residual field measurements, determining the extent of plastic deformation significant experimental challenges. The present effort seeks to offer direct insight into the nature of plastic strain generation in nickel single crystals subjected to melt-mediated laser processing. Ultra-high purity nickel single crystals were chosen for their FCC crystal structure and their lack of potential for dislocation interactions with either grain boundaries or solutes, thus significantly simplifying their analysis. [ABSTRACT FROM AUTHOR]

The microstructure evolution and mechanical properties of a Fe-Mn-Al-C austenitic low-density steel at different hot-rolling reductions have been investigated. It was found that with the increase in hot-rolling reduction from 45% to 82%, the grain size was uniformly refined and the dislocation density was continuously increased. As a result, both yield strength and ultimate tensile strength were effectively enhanced while the ductility and toughness only slightly decreased. An excellent combination of yield strength, ultimate tensile strength, total elongation, and toughness of 648 MPa, 976 MPa, 50%, and 105 J/m2, respectively, was obtained. The yield strength increment was interpreted by the stronger grain boundary strengthening and dislocation strengthening, and the minor loss of ductility and toughness was arising from the faster saturation of the slip band refinement (slip band spacing reached ∼50 nm) and an earlier occurrence of microbands due to the finer grain size. Based on this research, it is proposed that increasing the hot-rolling reduction was an effective approach to enhance the overall mechanical properties of the low-density steel with a fully austenitic microstructure. • Excellent ductility was kept while strength was enhanced by increasing hot-rolling reduction. • The increase in hot-rolling reduction effectively refined the mean grain size. • Stronger grain-boundary and dislocation strengthening led to improved yield strength. • The slip band spacing was reduced with finer grain size at the same strain level • Ductility decreased due to earlier saturation of slip band refinement and formation of microbands. [ABSTRACT FROM AUTHOR]

Abstract Microstructures and dislocations associated with the slip band (SB) fatigue cracks were investigated in Cu single crystal and bicrystal. It is found that there are high strain localizations with abundant dislocation cells around the cracked SBs. Due to the high local strain and slip irreversibility, the lattice rotates severely leading to large misorientation and hence low- or high- angle grain boundaries could form between the neighboring cells. Moreover, the dislocation walls can serve as preferential sites for nucleation and propagation of fatigue cracks with high density of dislocations, vacancies and high strain incompatibility. Graphical Abstract Unlabelled Image Highlights • Dislocation cells form near early slip bands fatigue cracks in wavy-slip materials. • Lattice rotates severely and grain boundaries form between neighboring cells. • The walls of dislocation cells are preferential sites for fatigue cracking. [ABSTRACT FROM AUTHOR]

A group of Ti-27Nb-7Fe-xCr (x = 0, 2, 4, 6, 8 wt%) alloys were designed on the basis of the DV-Xα cluster method, molybdenum equivalent and valence electron to atom ratio. The designed alloys were produced using the cold crucible levitation melting process for studying their microstructures and mechanical properties. The alloying of Cr renders a dual phase microstructure composed of a dominant β and a small amount of orthorhombic α'' formed in the Ti-27Nb-7Fe alloy to a single β phase microstructure formed in the alloys containing Cr. In the present work, yield strength is influenced by the effects of solid solution strengthening and fine grain strengthening, whereas hardness is influenced by the phases present and the level of the β stability. None of the investigated alloys fail until the load reaches 100 kN and all demonstrate impressive maximum compressive strength (~ 2 GPa) as well as plastic strain (> 26%). Young's modulus decreases from 116 GPa (for Ti-27Nb-7Fe) to 72 GPa (for Ti-27Nb-7Fe-8Cr) as the β stability improves. Moreover, the analyses of slip band patterns around the hardness indentation, wear resistance indices (i.e. H/E and H 3 /E 2 ) and elastic energies of the Ti-27Nb-7Fe-xCr alloys are carried out in the present work. [ABSTRACT FROM AUTHOR]

In this study, (austenite+ferrite+κ-carbide) triplex microstructures were obtained from the hot-rolling and subsequent 800 °C-annealing of Fe-0.8C-(12,15,20)Mn-7Al (wt%) lightweight steels, and their effects on ultra-high strength along with good ductility were investigated in relation with microstructural evolutions occurring during the tensile deformation. In the 12-wt%-Mn hot-rolled specimen, lamellar κ-carbides were populated along austenite grain boundaries, which seriously deteriorated the ductility. When the Mn content increased to 15 or 20 wt%, the volume fraction of κ-carbide decreased, and slip bands were sufficiently formed inside austenite grains during the deformation, which resulted in excellent ductility as well as ultra-high strengths. Very high yield strength was also achieved by forming triplex microstructures, in which the austenite deformed during the hot rolling greatly contributed to the strength enhancement. In the 800 °C-annealed specimens, the decreased volume fraction and morphological change from lamellar to polygonal-particle type of κ-carbides enhanced the ductility in spite of the slightly reduced strengths. This was because slip bands were sufficiently formed in austenite grains during the deformation, while voids were formed inside well-developed slip bands. The existence of a large amount of austenite was highly valuable for increasing the ductility by developing fine dislocation substructures such as Taylor lattices as a key feature of deformation mechanisms. [ABSTRACT FROM AUTHOR]

Deformation and crack initiation of industrial Ti-6Al-4V titanium alloy sheet were investigated using in-situ scanning electron microscopy (SEM) at room temperature. The results showed that slip band originated from α/α and α/β interfaces when the tension reaches the yield stage, and the slip mode develops from single slip to multi slip and finally the cross-slip occurs. Microcracks initiate primarily at the phase boundary or along the slip band within α phase, cracks are mainly connected along the 45° line. The fracture surface is full of dimples. Intergranular cracking is the main fracture mechanism. [ABSTRACT FROM AUTHOR]

A micromorphic single crystal plasticity model is formulated at finite deformations as an extension of Mandel’s classical theory based on a multiplicative decomposition of the deformation gradient. It involves a single microslip degree of freedom in addition to the usual displacement components. Two main variants of the constitutive equations are proposed. The first one relies on a Lagrangian microslip gradient and leads to a Laplace term in the isotropic hardening law. In contrast, the second formulation, based on a generalized strain measure defined with respect to the intermediate configuration, is shown to induce both isotropic and kinematic enhanced hardening. The first formulation is implemented in a 3D finite element code. The model is applied first to strain localization phenomena in a single crystal in tension undergoing single slip. The regularization power of the model is illustrated by mesh-independent simulations of the competition between kink and slip bands. The model is then used to investigate void growth and coalescence in FCC single crystals. Cylindrical and spherical voids are considered successively. The simulations show, for the first time in the case of spherical voids embedded in a single crystal matrix, that smaller voids grow slower than bigger ones, and that the onset of void coalescence is delayed for smaller voids. These results are related to the fact that the field of plastic slip is found to be more diffuse around smaller voids. [ABSTRACT FROM AUTHOR]

• The local slip band in the grain orientation provided the preferred path for fatigue crack growth. • The fracture energy of 12 slip systems in the optimal {111}<110>slip system family was calculated through molecular dynamics. • A micro damage evolution model based on fracture energy was established to predict the fatigue life of IN 750H. • The proposed model can better realize the dynamic process of fatigue crack initiation and growth stage. The cyclic stress responses and microstructure analyses were carried out of short-term aged Inconel 750H under high temperature low cycle fatigue tests, the influence of strain amplitude on fatigue fracture mechanism of aged IN 750H was systematically analyzed. According to the slip traces, Schmid factor, and geometrically necessary dislocation density distribution on the fracture frontier, the paper revealed that the local slip band provided a preferred path for the fatigue crack growth of Inconel 750H. Due to the limitation of the inability to measure energy of slip system through experiments, a probability based statistical method on average fracture energy of the slip system was constructed. Coupling with the macro-scale constitutive models, a microstructural-sensitive strategy based on fracture energy exhaustion theory was established. Based on the proposed model, the dynamic process of fatigue crack initiation and growth stage were simulated. The predictive fatigue lives showed a good consistence with the experimental results of both as-received state and short-term aged Inconel 750H under various amplitudes. In addition, the validity of the proposed model was further confirmed by fatigue crack length under the initiation and propagation stages, accompanying by the 3D X-ray computed tomography. [ABSTRACT FROM AUTHOR]

• An in-situ test system combined with DIC is developed under SEM, which can capture the SB evolution and microcrack nucleation. • For circular hole on SX superalloy, effects of secondary orientation and temperature on tensile behavior and SB evolution are revealed. • A SB evolution model is proposed, which uses different CRSSs as the plasticity criteria and internal state variables inside and outside SB. • The proposed model can simulate the SB evolution, SB direction, SB-induced strain concentration, and microcrack nucleation. Circular holes on single crystal (SX) superalloys are widely utilized as film cooling structures on SX turbine blades, while their failure is a persistent issue. This study presents in-situ tests using digital image correlation (DIC) to reveal the slip band (SB) evolution behavior near the circular hole on SX superalloy, and proposes a mechanism-based model to capture the SB-associated evolutions of stress, strain, and damage fields. In the experiment part, high-temperature in-situ tensile tests are carried out under scanning electron microscope on plate-like SX specimens with circular hole, which can achieve the in-situ measurement and observation for the SB-induced strain concentration and microcrack nucleation. Experimental results reveal the effects of secondary orientation and temperature on stress-strain curve, SB evolution and SB direction. Besides, the microstructure observation shows that the γ´ phase shear is the primary cause of strain concentration inside SB. In the simulation part, a physics-based SB evolution model is proposed under the framework of crystal plasticity. For the regions inside and outside SB, different critical resolved shear stresses are utilized as the plasticity criteria, and different slip resistances are used as internal state variables in the flow rule to simulate the SB-induced strain concentration. A damage evolution rule is developed based on the plastic work density in slip systems to simulate the microcrack nucleation near the hole edge. Finally, the proposed model is validated through the experiments. The model can effectively simulate the SB initiation/evolution, SB direction, SB-induced strain concentration, and the microcrack nucleation near circular hole on SX superalloy. [ABSTRACT FROM AUTHOR]

Small-scale mechanical testing techniques are currently being explored and developed for engineering applications. In particular, micro-tensile testing can add tremendous value, since the entire stress-strain curve, including the strain to failure, can be measured directly. In this work, 304 stainless steel specimens irradiated with 2 MeV protons to 10 dpa (full-cascade setting in the Stopping and Range of Ions in Matter, SRIM, software) at 360 °C was evaluated using micro-tensile testing. It was found that even on the micron scale, the measured strain corresponds well with macroscopic expectations. In addition, a new approach to analyzing sudden slip events is presented. [ABSTRACT FROM AUTHOR]

(Mg,Zn) 3 Gd precipitates were observed in the form of parallel arrays within a α-Mg matrix of a Mg-3.5Gd-1Zn-0.6Zr (GZ41K) alloy following isothermal holding at 450 °C for 20 min or uniaxial hot compression testing at 450 °C and at strain rates of 10 − 3 s − 1 and 10 − 1 s − 1 . A microstructural analysis using a combination of scanning and transmission electron microscopies showed arrays of precipitates nucleated on stacking faults as a result of the LPSO structures decomposing statically after long isothermal holding times at 450 °C, which is lower than the dissolution temperature of (Mg,Zn) 3 Gd precipitates (520 °C), and dynamically, as a result of hot compression. The presence of precipitates on slip bands was also observed in the case of deformed specimens. The characteristics of the precipitates were investigated using differential thermal analysis, and optical and electron microscopy. The influences of the solutionizing temperature and deformation conditions on distribution, morphology and volume fraction of precipitates were quantified. The results are interpreted in terms of the influence of the strain rate in increasing the stacking fault/dislocation intersections and the decomposition of the L1 2 structure of stacking faults. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) grain boundary sliding (GBS), which is useful for phenomenological understanding of superplastic and near-superplastic deformation, was achieved during a high-temperature shear test in oxide-dispersion-strengthened ferritic steel exhibiting anisotropic microstructure with largely elongated and aligned grains. In this study, 2D GBS, dislocation slip and subsequent microstructural evolutions were examined using surface markers drawn by focused ion beam and electron back-scattered diffraction analysis. In the near-superplastic state (region III), GBS was accommodated by transgranular dislocation activities initiating from grain protrusions or triple junctions into core areas, as described by the Ball–Hutchison model. The accommodation mechanisms were determined by the microstructural correlation between GBS-triggered stress concentration and available slip orientation and were closely related to the angle θ between GBS and dislocation slippage. When θ was small, GBS tended to be accommodated by a group motion of dislocations belonging to <111> {110} or <111> {112} slip systems (slip-band type). When θ was large, GBS tended to be accommodated by intragranular dislocation accumulation, which led to the development of sub-boundaries along {110} planes via dynamic recovery (sub-boundary type); this would be the origin of continuous dynamic recrystallization. [ABSTRACT FROM AUTHOR]

Effect of coherent L1 2 nanoprecipitates on the tensile behavior of a novel-designed Al 0.2 CrFeCoNi 2 Cu 0.2 high-entropy alloy is investigated in this study. Different heat treatments after cold rolling were used to achieve the alloys with two different microstructures. One is composed of a fcc matrix and coherent L1 2 (Ni,Cu) 3 Al nanoprecipitates after annealing at 700 ° C for 20 h; the other owns a fcc single-phase structure after annealing at 800 °C for 1 h as reference. Furthermore, the two alloys have nearly identical average grain sizes (~4.5 µm), and thus the exclusive effect of L1 2 nanoprecipitates could be identified by directly comparing their tensile behaviors. It is shown that the presence of L1 2 nanoprecipitates results in increases of 259 MPa and 316 MPa in the yield strength and ultimate tensile strength, respectively, accompanied by the maintenance of a high elongation (30.4%). This excellent strengthening effect is explained by the interaction between dislocations and L1 2 nanoprecipitates during the tensile straining process. Dislocation shearing of the L1 2 nanoprecipitates, which is evidently observed and also verified by the yield strength increment calculation, leads to predominant planar dislocation glide and the formation of crystallographically aligned slip bands as the main deformation mechanism, eventually resulting in a considerable work-hardening capacity enhancement with almost none harm to the elongation. [ABSTRACT FROM AUTHOR]

Hadfield steel is characterized both by high wear-resistance and ability to strain hardening. Due to these properties Hadfield steel is widely used in various industrial applications. The present investigation is aimed at analyzing the deformational behavior of Hadfield steel single crystals with [10 7 1] and [ 3 4 ̅ 2 ̅ ] compression and friction axis orientations, respectively. Consecutive experiments under constant loading conditions have demonstrated the deformation-induced relief development stages as well as succession of slip system activation in the process. Both slip band step height and inter-band space increased due to the development of the maximum stress concentration zone and distortions of the near-end zone. The sequence and direction of the shear in the analyzed systems are ascertained by analyzing the shear stress value and the deformation relief. [ABSTRACT FROM AUTHOR]

Light-weight high-manganese steels offer a high potential for industrial application due to their excellent combination of mechanical properties and reduced density. In the present work, the deformation behavior of an Fe-29.8Mn-7.65Al-1.11C steel was investigated by means of TEM microstructure analysis and XRD texture measurements. CALPHAD calculations were used to determine the processing parameters for the applied heat treatments in order to produce essentially different initial microstructures, i.e. single-phase austenite in homogenized condition with large grain size (state A), 2-phase steel composed of austenite and κ-carbides in aged condition with large grain size (state B), and single-phase austenite in recrystallized condition with fine grain size (state C). Since this is the first study to directly compare the plastic deformation of the same alloy with and without κ-carbides, the influence of the precipitation state could be successfully identified. Although the mechanical properties were strongly affected by grain size and precipitation state, the developed deformation microstructures and textures appeared very similar and evidenced the activation of the same deformation mechanisms in the material in states A, B, and C. The strong work hardening in these alloys was facilitated by planar dislocation glide leading to slip band refinement, i.e. Slip band Refinement-Induced Plasticity (SRIP) rather than microband formation. The reasons for this deformation behavior as well as its influence on the evolution of rolling and tensile textures are discussed. [ABSTRACT FROM AUTHOR]

Four alloys based on the Fe–30Mn–(8.5–12)Al–(1.0–1.3)C (wt%) system were prepared to investigate the effects of microstructure evolution and κ-carbide precipitation behavior on hot ductility behavior of austenitic lightweight steels. Hot tension tests were carried out at temperatures of 500–1230 °C using a Gleeble simulator. At high temperatures above 1000 °C, dynamic recrystallization occurred in all alloys, leading to high tensile ductility. At temperatures of 700–900 °C, the ductility decreased in all alloys due to the intragranular precipitation of κ-carbide, with increases in the amounts of Al and C contents then leading to a greater loss of ductility due to the formation of coarse intergranular κ-carbides. The addition of Cr and Mo suppressed the precipitation of κ-carbide, reducing the extent of ductility loss. At 500 °C, the ductility was recovered due to a reduction of inter-/intragranular κ-carbide precipitation and the development of slip bands caused by planar gliding of dislocations through κ-carbide shearing. The spacing among slip bands then became coarse with an increase in the Al and C contents, resulting from the coarsening of κ-carbide. Meanwhile, dynamic strain aging (DSA) behavior was observed in all alloys deformed at 500 °C. This occurred because the hot tensile tests were carried out under a high strain rate condition; therefore, the mobility of the dislocations was fast and thus solute atoms pinned the dislocations despite deformation at a high temperature. With a coarsening of κ-carbide, the extent of serration was reduced, resulted from the fact that the content of solute C decreased due to the greater precipitation of κ-carbide; i.e. , the amounts of solute C atoms to cause the DSA behavior were reduced. • Tensile ductility of lightweight steels changed greatly depending on the temperature. • At high temperature (>1000 °C), the ductility increased by dynamic recrystallization. • Ductility dip phenomena appeared at temperatures in the range of 700–900 °C. • Excessive κ-carbide precipitation caused a ductility dip with intergranular cracking. • Activation of planar gliding of dislocations at 500 °C recovered the ductility. [ABSTRACT FROM AUTHOR]

• Slip bands initiated inside martensitic laths, are oriented parallel to the lath. • Internal slip bands of the martensitic laths cause cracks to initiate. • Crack are more likely to propagation along the martensitic laths. • The complex structure of martensite has a greater resistance to small crack growth. Martensitic steel presents high fatigue crack resistance due to its complex and hierarchical microstructure, but its mechanisms are unclear. This work experimentally investigated effect of the lath and the prior austenitic grain (PAGs) on crack initiation and the early propagation behavior in high cycle fatigue. It is found that micro cracks initiated from the slip bands in the interior of thin monocrystalline laths, in which the dislocation intensity zones deflected the crack path. Subsequently, the micro cracks coalesced through the lath boundaries, and resulted in an intermittent and staggered appearance of crack path in the PAGs. Finally, the crack propagation across the boundaries of the primary PAG are extremely slow and presents significant zigzag manners due to the misorientation of the laths in neighboring PAGs. The above observations demonstrate that the crack initiation and early propagation are significantly hindered by the multi-scaled microstructure of the martensitic steel. [ABSTRACT FROM AUTHOR]

In the present study an attempt has been made to understand the high strain hardening in austenitic low-density steel using two full field measurements of temperature and strain on the sample during tensile deformation. Based on these measurements' evolution of energy storage during deformation was calculated. High energy storage has been attributed to the interaction between dislocation groups belonging to different slip bands and destruction of short-range order (SRO) clusters. This in turn, dictates the range of the elastic stress field of slip bands. Furthermore, weak deformation heterogeneity ensued just after yield and continued with a fixed strain pattern up to facture. This did not result in macroscopic instability but manifested as microstructural heterogeneity in the form of micro-band and nano twins at later stages of deformation. A mathematical model of energy storage based on dislocation entrapment is discussed. [ABSTRACT FROM AUTHOR]

A local approach coupling atomic force microscopy (AFM) observations and polycrystal finite element calculations is proposed to provide data at the slip-band scale. From AFM measurements of slip bands emerging at the specimen surface during tensile loading, and from numerical results of strain fields at the grain scale, the method is able to determine at the local discrete scale the mean slip-band spacing and the number of dislocations emerging during the plastic strain. The methodology applied in the hydrogen embrittlement context highlights, quantitatively, at the grain scale an increased plastic strain localization with internal hydrogen. [ABSTRACT FROM AUTHOR]

• CuCrFeMnNi-based welds showed Cu-rich phase separation with FCC structures. • Cu-rich phases enhanced the tensile properties of CuCrFeMnNi-based weld. • The dislocation movement and slip bands in WM were hampered by forming Cu-rich phases. • Cu-rich phases produced by Cu addition improved the weldability of HEA. This study investigates the gas tungsten arc weldability of the high-entropy alloy CoCrFeMnNi using CoCrFeMnNi and CuCrFeMnNi fillers. The CoCrFeMnNi-based weld had the same face-centered cubic (FCC) structure as the base metal, and the CuCrFeMnNi-based weld exhibited phase separation of the Cu-rich phase in addition to the FCC structure. Although the grain size of the CuCrFMnNi-based weld was similar to that of the CoCrFeMnNi-based weld, the Cu-rich phase formed in the CuCrFMnNi-based weld enhanced its tensile properties. This occurred because the dislocation movement and slip band in the weld metal were hindered by the formation of the Cu-rich phase. [Display omitted] [ABSTRACT FROM AUTHOR]

High angular resolution electron backscatter diffraction has been used to quantify the local elastic field at the tip of mechanically loaded intragranular slip bands observed in situ in the ferrite grains of an age-hardened duplex stainless steel (Zeron 100). The surface elastic strain field was integrated to calculate in-plane and out-of-plane surface displacements. This allowed the elastic fields to be parameterised in a finite element analysis, which used the displacement field as the boundary conditions, to obtain the potential strain energy release rate (J -integral) and three-dimensional stress intensity factors (K I , I I , I I I). This new analysis method is demonstrated by examining the elastic fields around the tip of an incipient slip band, an array of slip bands and the loading of a slip band. Direct measurement of the stress tensor in the grain identified the active slip systems with the highest Schmid factor. The stress intensity factors ahead of the slip band, measured under load, were directly affected by the magnitude of loading and the inclination angle of the slip band to the observed surface. [Display omitted]. [ABSTRACT FROM AUTHOR]

The interaction between dislocation pile-ups and grain boundaries gives rise to heterogeneous stress distributions when a structural metal is subjected to mechanical loading. Such stress heterogeneity leads to preferential sites for damage nucleation and therefore is intrinsically linked to the strength and ductility of polycrystalline metals. To date the majority of conclusions have been drawn from 2D experimental investigations at the sample surface, allowing only incomplete observations. Our purpose here is to significantly advance the understanding of such problems by providing quantitative measurements of the effects of dislocation pile up and grain boundary interactions in 3D. This is accomplished through the application of differential aperture X-ray Laue micro-diffraction (DAXM) and high angular resolution electron backscatter diffraction (HR-EBSD) techniques. Our analysis demonstrates a similar strain characterization capability between DAXM and HR-EBSD and the variation of stress intensity in 3D reveals that different parts of the same grain boundary may have different strengths in resisting slip transfer, likely due to the local grain boundary curvature. [ABSTRACT FROM AUTHOR]

Fatigue crack initiation and early short crack propagation behaviour in two microstructural variants of a recently developed Low Solvus, High Refractory (LSHR) disc superalloy at room temperature has been investigated by three-point bending with replication procedure. The results shows that fine gained (FG) LSHR possesses higher fatigue life due to its better crack initiation resistance, limited crack coalescence and comparable Stage I crack propagation resistance to the coarse grained (CG) LSHR, although its resistance to Stage II crack propagation is inferior. Twin boundary (TB) cracking in the relatively large grains dominates the crack initiation process along with occasional crack initiation due to slip band cracking. Activation of the primary slip systems parallel to the TB at matrix and twin and high resolved shear stress associated with high Schmid factor (SF) are required for TB crack initiation. Cracks preferentially propagate along slip bands associated with high SF slip systems after initiation. But cracks also propagate along slip bands associated with slip systems with lower SF if the inclination angle between the slip band ahead of the crack tip and the crack segment of the crack tip is small enough to enable a steady transition (or non-deflected growth) of cracks across the grain boundary. [ABSTRACT FROM AUTHOR]

In situ scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis were performed on the duplex Fe–27Mn–11.5Al–0.95C steel at room temperature to examine the tensile deformation behavior. The steel consisting of stable austenite matrix and a small amount of ferrite exhibited excellent combination of high strength and ductility (46.5 GPa%) in solid solution state due to the continuous strain hardening behavior. In situ SEM revealed that slip bands appeared in the austenite grain at the early deformation stage, and different slip systems intersected with higher density as the displacement increased. The deformation strains of austenite were obviously larger than that of ferrite, which resulted into the ferrite crack propagation at the later stage. With the stack fault energy (SFE) of ∼80 mJ/m 2 , the evolution of dislocation substructure with increasing strain shows typical planar glide characteristics, namely, dislocation pile-ups, Taylor lattice, high density dislocation walls, domain boundary and intersected microbands. Grain subdivision by microband intersection at high strains results in stable work hardening rate and continuous strain hardening behavior. [ABSTRACT FROM AUTHOR]

Deformation mechanisms of an Ni-based superalloy during low-cycle fatigue at various temperatures were studied. A new configuration of cross-slip dislocation was observed in the γ matrix during the deformation at 760 and 900 °C, which is an important component of the slip band at 900 °C. Slip bands with different morphologies were observed at room temperature and 900 °C, corresponding to the obvious work-hardening. It was observed that stacking faults spread throughout the γ/γ′ interface. [ABSTRACT FROM AUTHOR]

To examine the local conditions necessary to create cracks around cyclic slip bands, we studied the evolution of surface topography by atomic force microscopy and deformation localization by transmission electron microscopy for a wide structural variety (grain and precipitate sizes) in nickel-base alloys. We observed that the variance σ 2 associated with height emergence of deformation bands correlated directly with the type of bands, i.e. shear bands (SBs) or persistent slip bands (PSBs). An increase in the diameter of shearing precipitates induced a progressive transformation of SBs to PSBs with a decrease in the variance σ 2 . Surface analyses showed that a critical value of the local irreversible plastic strain accumulated in the band ( γ irr,pl,loc ) was necessary to for crack initiation. The value of γ irr,pl,loc increased with a progressive transformation of SBs to PSBs and the increase in band thickness. This last parameter is an internal length scale that plays an important role in diffusion of vacancies in accordance with Repetto’s model of crack initiation. [ABSTRACT FROM AUTHOR]

The components of power generations are subjected to the repeated thermal strain, owing to the temperature fluctuations associated with start-up and shut-up. Therefore, fatigue properties of the candidate materials are essential to be understood. To fully elucidate the fracture mechanism and microstructure evolution of the Nickel-based alloy under high-temperature cyclic loading, low cycle fatigue tests were carried out under the strain amplitude of 0.4%, in which temperature was in the range of 700–800 °C and strain rates from 5 × 10−4 s−1 to 5 × 10−3 s−1. The fatigued specimens were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), and electron backscatter diffraction (EBSD) observations. Slip band deformations mainly dominated under the temperature of 700 °C and 720 °C, and paralleled dislocation transmissions around twin boundaries were dominant under 750 °C. While free dislocation lines were typical dislocation configurations in 800 °C. Due to stress concentration caused by the accommodated dislocations, some cracks preferred to propagate along the twin boundary. Molecular dynamics simulated the dynamic interaction between dislocation and twin boundary at 750 °C. Dislocation movement was constrained on the twin boundary, which was verified by molecular dynamics simulations. As the temperature increased, the strength of the grain boundary degraded, and the fracture pattern changed from totally transgranular to both transgranular and intergranular cracking. • With the increase in temperature, dislocation configuration changes from slip bands to free dislocation lines. • Dislocation movement is constrained on the twin boundary, which is verified by molecular dynamics. •. [ABSTRACT FROM AUTHOR]

The interaction between slip bands and grain boundaries in commercial-purity titanium was examined using cross-correlation-based electron backscatter diffraction. At a low strain level, three types of interactions were observed: blocked slip band with stress concentration; slip transfer; and blocked slip band with no stress concentration. The stress concentration induced by the blocked slip band was fitted with Eshelby's theoretical model, from which a Hall-Petch coefficient was deduced. It was found that the Hall-Petch coefficient varies with the individual grain boundary. We investigated the geometric alignment between the slip band and various slip systems to the neighbouring grain. Stress concentration can be induced by the blocked slip band if the slip system is poorly aligned with 〈a〉 prismatic, pyramidal or basal slip systems in the neighbouring grain. Transfer of slip across the boundary occurs when there is good alignment on 〈a〉 prismatic or 〈a〉 pyramidal slip systems. Other stress-relieving mechanisms are possible when the best alignment is not with the slip system that has the lower critical resolved shear stress. [ABSTRACT FROM AUTHOR]

Abstract: A Cu bicrystal with a twin boundary (TB) inclined at 45° to the loading direction and its component monocrystal were specially designed to reveal their fatigue cracking mechanisms. Experimental results show that slip bands (SBs) parallel to the TB plane operated easily in both component grains and concentrated at the TB, while the SBs distributed more homogeneously in the monocrystal. It was revealed by atomistic modeling simulations and anisotropic elasticity theory that the screw dislocations transmitted to the TB could dissociate into two far-separated partial dislocations. Therefore, these dislocations would be confined in the TB with a high difficulty of cross-slip, leading to strain localization near the TB. With cyclic deformation, the fatigue crack nucleated along the TB preferentially in the bicrystal with fewer cycles than that for the SB crack in the monocrystal. Besides, unlike the impingement fatigue crack along high-angle grain boundaries with dislocation impingement, the shear fatigue crack initiates along the TB devoid of dislocation pile-ups. The existence of the TB inclined at 45° to the loading direction induces strain localization and early intergranular fatigue cracking in the Cu bicrystal. These results could not only expand our knowledge of fatigue cracking mechanisms by clarifying how the boundary behaves without the piling up of dislocations, but also provide important implications for future interfacial optimization of materials. [Copyright &y& Elsevier]

Abstract: The purpose of this study is to investigate the effects of a nano-scale stress-field on fatigue damage in a nano-copper component under fully-reversed and high-cycle loading. A resonant fatigue experiment is carried out for a cantilever micro-specimen that has a polycrystalline nano-Cu sandwiched by Si, Ti and SiN. Crystallographic slip bands associated with extrusion/intrusion of about 30nm width, which is much finer than that in the bulk copper (≈1μm), are formed on the Cu surface owing to the high-cycle fatigue loading. The new finding, the ultra-fine extrusion/intrusion, suggests the existence of different fatigue damage mechanisms in the nano-Cu from that in a bulk counterpart. The slip bands appear only in a particular grain though some others possess slip systems with higher Schmid factor. Detailed stress analysis, taking into account the Cu grains and surrounding dissimilar materials (Si, Ti, SiN), indicates that they are formed at a slip system with the highest resolved shear stress, which is in nano-scale. The formation stress is much higher than that in a bulk. [Copyright &y& Elsevier]

Abstract: A finite-deformation strain gradient crystal plasticity model is implemented in a three-dimensional finite-element framework in order to analyze the deformation behavior and the stress–strain response of magnesium single crystals under c-axis orientation. The potential-based and thermodynamically consistent material model is formulated in a non-local and non-linear inelastic context in which dislocation densities are introduced via plastic strain gradients. Experiments have shown that the internal length scale of the microstructure starts to affect the overall stress–strain response when the sample size decreases to the micron scale. As a consequence, strain gradients develop, leading to an additional energetic-like hardening effect which results in an increase of the macroscopic strength with decreasing crystal size. In the case of uniaxial compression of c-axis-oriented single-crystal micropillars, the model is able to predict the discrete dislocation glide in terms of a band-shaped slip zone. Two different pillar sample sizes are taken into account in order to investigate the intrinsic size effect during plastic deformation where the crystallographic orientation leads to the activation of pyramidal slip systems as reported in various experimental studies. The interaction of those slip systems is expressed in terms of latent hardening and excess dislocation development. A comparison between numerical results and corresponding experimental data is presented. [Copyright &y& Elsevier]

Strain localization is often observed in single and poly-crystals, for instance forming clear bands or persistent slip bands respectively during post-irradiation tensile loading or cyclic loading. This concerns FCC, BCC or HCP crystallographic structures. At the intersection of the so-called slip bands (SBs) and grain boundaries (GBs), stress concentration areas emerge contributing to intergranular microcrack initiation. Indeed, GB stress fields show singularities due to the SB plastic shearing of the surrounding elastic matrix. Since Stroh's work [[?]], GB normal stress fields have been computed using pile-up theory assumptions. However, as these approaches assume that slip occurs along only one single atomic plane, they overestimate GB normal stress fields because SBs generally display finite thickness, from a few ten nm to a few μm. Crystalline finite elements (FE) computations are carried out using the Cast3 M software. Meshed microstructure includes an elastoplastic SB within a main elastic grain which which is embedded at free surface of an elastic matrix. Results show in fact that using the pile-up formalism leads to large GB stress field overestimations. Therefore, an analytical formula describing the normal GB stress fields is proposed in the current paper, extend- ing the pile-up solution in the neighbourhood of the SB corner. The relationships between SB length and thickness and stress singularities are established in the light of the theory of matching asymptotic expansions. A double fracture criterion allows the prediction of intergranular microcrack initiation based on the computed stress singularities. Another analytical model based on the solution of the thermoelastic problem allow to propose a more general formula of the grain boundary stress fields accounting for the unloading effects. Using only one stress field computed by FE, the prefactors are computed and both analytical formulae are shown to be validated for all the range of grain size, SB thickness and remote applied stress. [ABSTRACT FROM AUTHOR]

The paper examines the role of the loading frequency on the dwell fatigue crack growth mechanism in the super-solvus nickel-based superalloy, ME3. This is accomplished by carrying out a set of crack growth experiments in air and vacuum at three temperatures; 650°C, 704°C and 760°C using a dwell loading cycle with hold time periods up to 7200s imposed at the maximum load level. Results of these tests show that the transitional transgranular/intergranular loading frequency is 0.1Hz, and are used to determine the apparent activation energy of the time-dependent crack growth process. Analysis of this energy in both air and vacuum showed that the intergranular cracking is governed by a mechanism involving grain boundary sliding. This mechanism is explained in terms of absorption of dissociated lattice dislocations into grain boundary dislocations. The gliding of these dislocations under shear loading is assumed to cause grain boundary sliding. A condition for this mechanism to occur, is that a critical minimum distance exists between slip bands impinging the affected grain boundary. This condition is examined by correlating the slip band spacing (SBS) and loading frequency using a model based on minimum strain energy accumulation within slip bands and that a unique configuration of number and spacing of bands exists for a given plastic strain. The model outcome expressed in terms of SBS as a function of loading frequency is supported by experimental measurements at both high and low loading frequencies. Results of the model show that a saturation of SBS, signifying a condition for intergranualr cracking, is reached at approximately 3μm which is shown to coincide with the transitional loading frequency of 0.1Hz. [ABSTRACT FROM AUTHOR]

Abstract: The DISFAT project is a French project financially supported by the French National Agency for Research (ANR). It aims at a deeper understanding of mechanisms leading to crack initiation in metals and alloys under Very High Cycle Fatigue loading (VHCF). The VHCF regime is associated with stress magnitudes lower than the conventional fatigue limit and as a result, numbers of cycles higher than 109. Tests were carried out using an ultrasonic technique at loading frequency of 20 kHz. In the case of pure copper polycrystals, we previously showed that slip band (SB) activity and intrinsic dissipation were closely related. Dissipation and slip band amount increased with the number of cycles. At very small stress amplitudes, no slip band appeared at the specimen surface up to 108 cycles but the material was found to dissipate energy. These results revealed that the material never reached a steady state and so could break at higher number of cycles. In this paper, the morphology and the location of slip bands were characterized. Different types of slip bands depending on the stress amplitudes appeared at the specimen surface. The stress amplitude required to show the first slip bands decreases with the number of cycles. It is twice lower than the stress amplitude required to break the specimen for the same number of cycles. At the smallest stress amplitudes, slip bands were mostly found at twin boundaries. Quasi 3D finite element simulations taking into account the polycrystalline nature of the material emphasized the key role of the elastic anisotropy in slip band initiation. A criterion for slip band appearance was finally proposed. [Copyright &y& Elsevier]

Abstract: Many components have to withstand a very high number of loading cycles due to high frequency or long product life. In this regime, the period of fatigue crack initiation and thus the localization of plastic deformation play an important role. Metastable austenitic stainless steel (AISI304) that is investigated in this study shows localization of plastic deformation in bands of intense slip. In order to provide a physically-based understanding of the relevant damage mechanisms under VHCF condition, simulation of irreversible damage accumulation in slip bands is performed. For this purpose, a microstructural simulation model is proposed which accounts for the damage mechanisms in slip bands documented by experimental results. The model describes the damage accumulation through formation of slip bands, sliding and multiplication of dislocations and the amount of irreversibility of such mechanisms in case of VHCF relevant loading conditions. The implementation of the simulation model into a numerical method allows the investigation of the damage accumulation in a real microstructure simulated on the basis of metallographic analysis. The numerical method used in this study is the two-dimensional (2-D) boundary element method which is based on two integral equations: the displacement and the stress boundary integral equation. Fundamental solutions within these integral equations represent anisotropic elastic behavior. By using this method, a 2-D microstructure can be reproduced that considers orientations as well as individual anisotropic elastic properties in each grain. Contours of shear stresses along most critical slip systems are compared with images of slip band formation at the surface of fatigued specimens provided by scanning electron microscopy (SEM). Results show that simulation of slip bands is in good agreement with experimental observations and that plastic deformation in slip bands has a high impact on shear stresses at grain boundaries acting as possible crack origin in the fully austenitic material condition. In contrast to most other publications in the field of fatigue simulation the present paper tackles the problem of modeling cyclic slip irreversibility and gives an insight into its effect on the microstructural damage evolution. [Copyright &y& Elsevier]

Abstract: In order to investigate the fatigue behavior of submicron metal components, a resonant fatigue experiment is conducted using a single-crystal gold specimen that possesses a test section with a submicron width. Crystallographic slip bands appear on the test section surface due to fatigue when the resonant frequency of the specimen decreases abruptly. These slip bands form due to activation of a slip system with the maximum resolved shear stress amplitude. The critical value for slip band formation is evaluated to be over 150MPa, which is over six times larger than that of persistent slip bands (PSBs) in the bulk counterpart. Cross-sectional field-emission scanning electron microscopy observations reveal that extrusions/intrusions that are ∼15nm wide form on the surface at slip bands. Although the slip bands have similar morphologies to those of PSBs, they are much narrower (bulk width is larger than 1μm). The high fatigue strength may be attributed to the narrow slips required. Strain localization at the slip bands is revealed by cyclic deformation in the surface-polished specimen after fatigue. This suggests that there may be a certain fatigue understructure at the slip bands. [Copyright &y& Elsevier]

Abstract: Fatigue crack initiation behavior in duplex stainless steel was studied in the embrittled condition (aging at 475°C for 100h) by interrupting fatigue tests conducted at different Δσ/2 values, identifying the crack initiation sites and relating them to the crystallographic parameters obtained from electron back scattered diffraction scans. From the fatigue crack initiation studies conducted at Δσ/2=400 and 500MPa, it was concluded that the crack initiation sites are the slip markings corresponding to {111} plane in austenite at 400MPa and more cracks were observed to initiate at twin boundaries in austenite at 500MPa in the aged condition. [Copyright &y& Elsevier]