Formation Of Dislocation Structures Research Articles

Local crack arrestability and deformation microstructure evolution of hydrogen-related fracture in martensitic steel

Intergranular cracks in the uncharged specimen were arrested at low-angle prior austenite grain boundary (PAGB) segments of several micrometers. In contrast, even small, low-angle PAGB segments with sub-micrometer sizes impeded the propagation of hydrogen-related intergranular crack. At the hydrogen-related quasi-cleavage crack tip, the crystallographic orientation changed abruptly, and deformation microstructures developed, including the formation of low-energy dislocation structures. A certain degree of crack growth resistance (intrinsic crack growth resistance) in the hydrogen-related fractures could be attributed to the intense localized plastic works involved in the arrest of intergranular cracks and the propagation of quasi-cleavage cracks.

Correlation between the micro-shot peening coverage and surface microstructural evolution and fluoride-induced corrosion behavior in Monel 400 alloy

This study examines the influence of micro-shot peening (MSP) on Monel 400 alloy, focusing on surface microstructural evolution and fluoride-induced corrosion behavior compared to its solution annealed (SAed) counterpart. MSP treatments were conducted at various surface coverages (100%, 200%, 500%, 1000%, 1500%, and 2000%). Characterization encompassed microhardness, surface roughness, grazing incidence x-ray diffraction (GI-XRD), field emission scanning electron microscopy (FE-SEM) with electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). With increasing the MSP coverage to 2000%, the surface crystallite size decreased from approximately ∼30 µm in the SAed sample to 60 nm. TEM analysis emphasized dislocation slip and formation of dislocation structures as the primary mechanisms for the grain refinement. However, the 2000% coverage exhibited microcrack formation, compromising its hydrofluoric (HF) corrosion resistance. Electrochemical tests revealed severe localized corrosion in all MSP-treated samples except the 1500% coverage, which exhibited a minimum passive current density of 0.2–1.0 µA/cm2. Inductively coupled plasma optical emission spectroscopy (ICP-OES) of immersion solutions showed lower copper and nickel ion concentrations (<150 ppm) in the 1500% MSP-treated sample, indicating its enhanced corrosion resistance. X-ray photoelectron spectroscopy (XPS) identified NiO, NiF2, CuO, CuF2, and Cu(OH)2 phases in SAed and 1500% MSPed samples, with a higher concentration of copper oxide (CuO) in the corrosion film of the 1500% MSP-treated sample, contributing to its superior corrosion resistance.

Effect of deformation temperature on strain localization phenomena in an austenitic Fe-30Mn-6.5Al-0.3C low-density steel

We have investigated the influence of the deformation temperature from 25 °C (RT) to -196 °C on the dislocation structures associated with strain localization phenomena in an austenitic Fe-30Mn-6.5Al-0.3C (wt.%) low-density steel by electron channeling contrast imaging (ECCI), electron backscatter diffraction (EBSD), and bright-field transmitted forescattered electron imaging ((BF) t-FSEI) techniques. The characteristics of the dislocation structures were evaluated on the main texture components, i.e. <111>//tensile axis, <112>//tensile axis, and <001>//tensile axis directions. The inhomogeneous character of the plastic behavior is promoted upon cryogenic deformation due to the formation of dislocation structures associated with strain localization, namely microbands (MBs) and deformation bands (DBs). ECCI analysis of the dislocation structure reveals that the deformation temperature has a strong influence on the thermal-assisted dislocation processes controlling the dislocation configurations and MB formation mechanisms. The MB nucleation mechanism evolves from a cross-slip-assisted mechanism at RT deformation conditions to a slip band-assisted mechanism at cryogenic deformation temperatures. This effect has a profound effect on the grain orientation dependence of the MB structure but not on its crystallographic alignment. On the other hand, cryogenic deformation temperatures (-196 °C) enhance the material's mechanical strength and ductility due to the activation of deformation twinning, which is associated with the reduction of the stacking fault energy. We find that MBs have a small contribution to strain-hardening and ductility due to the small mechanical resistance of these dislocation structures against the advance of deformation twins and dense dislocation layers, and the comparatively small plastic strain accommodated by them, respectively. These findings provide new insights into the microband-induced plasticity (MBIP) effect.

Dislocation structures formation induced by thermal stress in additive manufacturing: Multiscale crystal plasticity modeling of dislocation transport

The motion of dislocations governs the plastic deformation of crystalline materials, which in turn determines the mechanical properties. The complex thermal history, large temperature gradients and high cooling rates during the process of additive manufacturing (AM) can induce high dislocation density and unique dislocation structures in the material. The origin of these dislocation structures and their stability during mechanical loading are debated. A novel temperature dependent continuum dislocation dynamics (CDD) model is developed, in which four state variables are used for each slip system representing the total dislocation density, edge and screw geometrically necessary dislocation densities and dislocation curvature. The CDD model is fully coupled with a crystal plasticity solver, which captures the plastic deformation induced by the dislocation motion. A hybrid continuous and discontinuous Galerkin formulation is developed to accurately reproduce the dynamics of highly discontinuous dislocation density fields that are typical of dislocation structures. A multiscale modeling approach is used, in which the thermally induced deformation in specific grains of a polycrystal is extracted from larger scale crystal plasticity simulations of the laser powder-bed fusion process, and is then used for single crystal scale dislocation dynamics simulations. Simulation results reveal the dynamics of dislocation structure formation in grains at different positions during laser scanning and cooling stages. The effect of the cyclic thermal stress during multi-layer AM fabrication is also investigated. The simulations provide a new perspective on the specific conditions that should be satisfied during AM process for the formation of stable dislocation structures.

RELATION BETWEEN DISCONTINUOUS PLASTIC FLOW AND STRAIN HARDENING OF THE LOW-CARBON STEEL

Purpose. Determination of the conditions for the disappearance of a section of intermittent flow and its effect on the strain hardening of low-carbon steel.&#x0D; Actuality. The use of low carbon steels with intermittent flow for stamping has a significant limitation. Based on this, the issues of the effect of ferrite grain size on the occurrence of intermittent flow are relevant for determining the optimal structural state of steels intended for deep drawing.&#x0D; Research methods. The structure of the samples was studied under a light microscope, the grain size of the ferrite was determined by the methods of quantitative metallography. The mechanical properties of steel were determined in tension at room temperature and a strain rate of 10-3 s-1. The characteristics of the initiation of plastic flow and the parameters of strain hardening were determined from the analysis of tension curves in logarithmic coordinates. In the region of uniform strain hardening, the deformation of the violation of the directly proportional relation lgσ-lgε was determined as the moment of formation of dislocation structures with a certain periodicity.&#x0D; Results. An increase in the grain size of ferrite is accompanied by a decrease in the region of intermittent flow and a shift in the moment of formation of a dislocation cellular structure towards small plastic deformations. The strain hardening rate in the region of uniform work hardening and the Lüders strain are related by an inversely proportional relationship. With excessively large grain sizes of ferrite, the difficulty of maintaining conditions for a uniform distribution of slip lines is one of the reasons for the disappearance of the intermittent flow region on the deformation curves of low-carbon steel.&#x0D; Scientific novelty. With an increase in the grain size of ferrite, the deformation of the beginning of the decay of a uniform distribution of dislocations into periodic structures is shifted to a decrease. At the same time, an increase in the ability of the metal to work hardening during the formation of a deformation band contributes to a decrease in the length of the intermittent flow section.&#x0D; Practical value. Determining the nature of the influence of the grain size of low-carbon steel ferrite on the characteristics of work hardening and the formation of dislocation periodic structures can be useful in determining the optimal structural state of steel for deep drawing.

Characterization of dislocation microstructures in near-[formula omitted] single crystal copper using high-voltage scanning transmission electron microscopy

Metallic structures are prone to failure caused primarily by fatigue-related damage to the structural material. Fatigue behavior is strongly correlated with dislocation structures in metals. Therefore, investigating the formation of dislocation structures is essential for understanding the fatigue process. The dislocation structure in face-centered cubic crystals has a strong orientation dependence. However, the detailed characteristics and evolution process of dislocation structures of fatigued [1‾11] single crystal copper are still insufficient. This study investigated dislocation structures in near-[1‾11] single crystal copper cyclically deformed at room temperature under different constant plastic shear strain amplitude (γpl) to analyze the formation mechanism of dislocation structures and their relationship with fatigue behavior. Characteristic dislocation structures were characterized by adopting multiple planes using a high-voltage scanning transmission electron microscope. With increasing shear strain amplitude, a vein-like structure along the (1‾11) plane gradually developed into a wall structure. When γpl ≥ 1 × 10−3, deformation bands and cell bands were formed to accommodate the higher plastic strain. The state of cell-band development significantly affected the cyclic softening of the single crystal copper. A positive linear relationship existed between the shear stress amplitude and the reciprocal of the cell width.

Effect of strain of cryorolling on structure and strength of nickel

The effect of isothermal rolling at liquid nitrogen temperature with reductions up to 90 % on the structural-mechanical behavior of coarse-grained nickel was evaluated by TEM, SEM-EBSD and X-ray analysis methods, and microhardness measurements. The highest hardening rate of the metal was found at the initial stage of rolling (up to about 50 %), after which it decreased slightly with further reductions. Detailed analyses of the evolution of dislocation density, grain size and grain boundary spectra have shown that the behavior found was attributed to an extremely low deformation temperature, resulted in a decreased rate of accumulation of crystalline defects, as well as the formation and rearrangement of dislocation structure. Due to the strong suppression of dynamic recovery and recrystallization, even when rolling to a reduction of 90 %, a relatively homogeneous coarse-fibered structure with a developed nanocellular substructure and less than 5 % fraction of nanoscale dynamically recrystallized grains was formed. It was concluded that the main structural strengthening factors in cryogenically rolled nickel was the formation of low-energy dislocation structures and their transformations into a well-developed substructure with nanosized crystallites separated predominantly by low-angle boundaries.

Effects of plastic strain and reloading stress on the magneto-mechanical behavior of electrical steels: Experiments and modeling

The properties of electro-mechanical systems are intimately linked to the mechanical state of the materials used for their design. Notably, the processing stages can lead to significant mechanical stresses, with a strong impact on the final magnetic behavior, through plasticity and residual stress effects. This work presents a thorough magneto-mechanical characterization, both hysteretic and anhysteretic, of an electrical steel (DC04) at different levels of plastic deformation and applied tension stress. The mechanical characterization of the material leads to the identification of two hardening stages: a first stage attributed to the development of long-range internal back stress, and a second stage dominated by intragranular stresses connected to the formation of dislocation structures. The magnetic characterization shows that, under no applied stress, plastic strain involves a significant degradation of the magnetic behavior. Mechanical reloading allows recovering part of the magnetic properties of the virgin material. A simplified multiscale modeling tool is proposed for the magneto-mechanical behavior, including the effects of internal stress and dislocation density. The model is notably used to predict the effect of a reloading stress on the magnetic behavior of a plasticized material, with a very satisfactory agreement. For the first time, a three-dimensional modeling approach is proposed for the magneto-mechanical behavior of materials including levels of plasticity up to necking. The very low computation cost of the modeling approach makes it suitable for the numerical study of magnetic devices under various mechanical states. In addition, this formulation opens a route for estimating the mechanical state of a plastically deformed material through the analysis of its magnetic behavior.

The interplay of local chemistry and plasticity in controlling microstructure formation during laser powder bed fusion of metals

Additive manufacturing (AM) of metallic components promises many advantages over conventional manufacturing processes through high design flexibility across multiple length scales and precision coupled with an astonishing combination of mechanical properties. Characterizing the relationship between microstructure and mechanical properties remains one of the major challenges for this novel technology. A natural precursor is identifying the influence of the processing path on the developing microstructure. We combine experimental studies of single-track laser powder bed fusion (LPBF) scans of AISI 316L stainless steel, finite element analyses, and large-scale three-dimensional discrete dislocation dynamics simulations to provide a unique understanding of the underlying mechanisms leading to the formation of heterogeneous defect structures in additively manufactured metals. Our results show that the interruption of dislocation slip at solidification cell walls is responsible for the formation of cellular dislocation structures, highlighting the significance of solute segregation for plastic deformation of additively manufactured components. This work provides a mechanistic perspective on heterogeneous microstructure formation and opens the potential for a reliable prediction of the resulting mechanical properties of additively manufactured parts.

Formation of dislocation structures during cyclic deformation in near-[001] multiple-slip-oriented copper single crystals

Dislocation structures in [001]-oriented copper single crystals have historically been studied at relatively low plastic shear strain amplitudes (γpl). Herein, the dislocation structure is investigated across a wide γpl range of 1.7 ∙ 10−4–1.7 ∙ 10−2. When γpl < 1.5 ∙ 10−2, the dislocation structure comprised a labyrinth with a set of parallel (100) and (001) walls. However, as γpl approached 1.5 ∙ 10−2, the dislocation structure changed to a cell structure to accommodate the higher plastic strain. The formation plane of the cell boundary depends on which slip system is activated as the primary slip system.

Structure and residual stress distribution in TiNi substrate after fabrication of surface alloy using electron-beam treatments

In this work, an origin of the residual stresses formed in the sublayer of TiNi substrate adjacent to the [Ti-Ni-Ta-Si] surface alloy (SA) was proposed. The as-cast SA was fabricated through an additive thin-film electron-beam synthesis using a low-energy high current electron beam (LEHCEB) treatment of the [Ti60Ta30Si10 (at. %)/TiNi] system. An additional post-LEHCEB treatment was employed for the SA synthesis (denoted as EB-treated SA) in order to reduce the value of residual stresses. Based on the XRD, TEM/SEM/EDS data, it has been found that the transition zone between the outer SA zone and the TiNi substrate exhibits several sublayers: eutectic B2+Ti3Ni4, martensitic and heat-affected zone (HAZ). However, the martensitic interlayers formed beneath the as-cast and EB-treated SAs possess different types of martensitic structures. Indeed, in the as-cast SA the sublayer of TiNi substrate is a Ni-rich (Ti<50Ni>50) one, so the martensitic transformation В2→R takes place in this sublayer. In turn, in the EB-treated SA the TiNi sublayer shows the composition close to equiatomic (Ti∼50Ni∼50) one, therefore the В2→B19′ martensitic transformation has occurred. The formation of martensitic phases led to a partial decrease (by a factor of ∼1.5–2) of the residual stresses in the underlying HAZ of TiNi substrates. The mechanism of B2 phase stabilization in the HAZ is closely related with a substructural hardening accompanied by formation of dense dislocation structures and residual elastic stresses that could be relaxed through short-term annealings induced by electron beam treatments.

Monte Carlo-Discrete Dislocation Dynamics: a technique for studying the formation and evolution of dislocation structures

A novel Monte Carlo (MC) based solver for discrete dislocation dynamics (DDD) has been developed, by which dislocation lines are inserted to the system in succession subject to a user-defined acceptance criterion. Utilizing this solver, dislocation structure evolution can be examined in a controlled fashion that is not possible using conventional DDD methods. The outcomes of the MC-DDD simulations establish for the first time that dislocation wall structures can adopt a characteristic width that naturally arises from elastic interactions within the network. This characteristic width does not alter as additional dislocation lines are inserted and the density in the wall increases, meaning it is independent of the mean dislocation spacing. However, the wall width is influenced by the acceptance criterion used during MC steps; the wall gets thinner as the interactions within the wall become more attractive. Finally, we demonstrate that algorithmic aspects of MC-DDD simulations can provide insights into structure evolution. Overall, this new MC-DDD technique will allow systematic studies of dislocation structures, providing unprecedented insight into the underlying mechanics.

Fluctuations in crystalline plasticity

Recently acoustic signature of dislocation avalanches in HCP materials was found to be long tailed in size and energy, suggesting critical dynamics. Even more recently, the intermittent plastic response was found to be generic for micro- and nano-sized systems independently of their crystallographic symmetry. These rather remarkable discoveries are reviewed in this paper in the perspective of the recent studies performed in our group. We discuss the physical origin and the scaling properties of plastic fluctuations and address the nature of their dependence on crystalline symmetry, system size, and disorder content. A particular emphasis is placed on the associated emergent behaviors, including the formation of dislocation structures, and on our ability to temper plastic fluctuations by alloying. We also discuss the "smaller is wilder" size effect that culminates in a paradoxical crack-free brittle behavior of very small, initially dislocation free crystals. We show that the implied transition between different rheological behaviors is regulated by the ratio of length scales $R=L/l$, where $L$ is the system size and $l$ is the internal length. We link this new size effect with other related phenomena like size dependence of strength ("smaller is stronger") and the size induced switch between different hardening mechanisms. One of the technological challenges in nanoscience is to tame the intermittency of plastic flow. We show that this task can be accomplished by generating tailored quenched disorder which allows one to control micro- and nano-scale forming and opens new perspectives in micro-metallurgy and structural engineering of ultra-small load-carrying elements. These results could not be achieved by conventional methods that do not explicitly consider the stochastic nature of collective dislocation dynamics.

Dislocation density in cellular rapid solidification using phase field modeling and crystal plasticity

A coupled phase field and crystal plasticity model is established to analyze formation of dislocation structures and residual stresses during rapid solidification of additively manufactured 316L stainless steel. The work focuses on investigating the role of microsegregation related to the intra-grain cellular microstructure of 316L. Effect of solidification shrinkage is considered along with dislocation mediated plastic flow of the material during solidification. Different cellular microstructures are analyzed and the characteristics of the cell core, boundary and segregation pools are discussed with respect to heterogeneity of dislocation density distributions and residual stresses. Quantitative comparison with experimental data is given to evaluate the feasibility of the modeling approach.

On the microstructural evolution pattern of 300 M steel subjected to surface cryogenic grinding treatment

In the present work, an ultrahigh strength 300 M steel was treated by the surface plastic deformation with surface cryogenic grinding treatment (SCGT) technique. The SCGT was carried out by rotational grinding wheel embedded with numerous zirconium corundum abrasive grits, which contributes to a decreasing distribution of strain, strain rate and strain gradient from the treated surface to the matrix. The depth-dependent microstructural evolution was systematically evaluated from micrometer to nanoscale and in particular, the deformation mechanisms and texture alternation were addressed. It was identified that the microstructural evolution starts from the formation of dislocation structures, that is subsequently followed by the distorted microstructures featured as the origination and evolution of ultrafine laminates and ultrafine grains in the form of dislocation activities. Nanocrystalline was generated in the topmost surface region and nanoparticle precipitates induced by the SCGT process occur within a few microns of the treated surface. In SCGT, a very high strain rate of over 10 6 s −1 and a strain gradient of over 0.2 μm −1 were induced on the topmost surface of 300 M steel sample, which impels the martensite-matrix lamella extended into the elongated structure and finally transformed into the nanosized grains during processing. A dislocation slip-dominated process that was supplemented by the mechanical twinning governs the microstructural evolution pattern during the SCGT process, the nucleus of dynamic recrystallization initiated from the pre-existing dislocation cells were observed, and the transformation from martensite to austenite was effectively suppressed. The increase of grain size from nanoscale to submicron and finally microscale contributes to a decrease of microhardness by 25.6% (from 7.8 GPa at the treated surface to 5.8 GPa at a depth of over 100 μm from the processed surface). • Gradient microstructures are observed after being subjected to the SCGT process • Nanoparticle precipitates induced by the SCGT process appear within a few microns of the treated surface • A dislocation slip-dominated process governs the microstructural evolution pattern • The relationship between the microstructural evolution and microhardness is analyzed

Deformation mechanisms of CoCrFeMnNi high-entropy alloy under low-cycle-fatigue loading

Plastic deformation during low-cycle fatigue (LCF) in equiatomic face-centered cubic (FCC) CoCrFeMnNi high-entropy alloys (HEAs) is accumulated by dislocation substructure formation, which leads to crack initiation. Whilst these substructures have been reported before, little has been done to clarify their formation mechanisms and the effects of strain amplitude, cycle number and grain orientation. In this study, cyclic deformation behavior and microstructural evolution of CoCrFeMnNi were examined for two different grain sizes at room temperature. Microstructural investigations by transmission electron microscopy showed that, while the dislocation structures at low strain amplitude (0.3%) mainly consisted of planar slip bands, at higher strain amplitudes (0.5% and 0.7%), wavy-substructures including veins, walls, labyrinth and cells prevailed. Slip mode also changes from initially planar-slip to wavy-slip with cycle numbers. Dislocations in veins, walls, labyrinth and cells are found to have different Burgers vectors, suggesting that apart from wavy-slip, multiple-slip also contributes to their formation. Moreover, distinct dislocation substructure in grains is dictated more by the constraints from neighboring grains rather than by their orientation. Additionally, the formation of various dislocation structures in a single grain is also linked to the constraint effects from the neighboring grains.

Deformation Mechanisms of CoCrFeMnNi High-Entropy Alloy Under Low-Cycle-Fatigue Loading

Plastic deformation during low-cycle fatigue (LCF) in equiatomic face-centered cubic (FCC) CoCrFeMnNi high-entropy alloy (HEA) is accumulated by dislocation substructure formation, which leads to crack initiation. Whilst these substructures have been reported before, little has been done to clarify their formation mechanisms and the effects of strain amplitude, cycle number and grain orientation. In this study, cyclic deformation behavior and microstructural evolution of CoCrFeMnNi were examined for two different grain sizes at room temperature. Microstructural investigations by transmission electron microscopy showed that, while the dislocation structures at low strain amplitude (0.3%) mainly consisted of planar slip bands, at higher strain amplitudes (0.5% and 0.7%), wavy-substructures including veins, wall, labyrinth and cells prevailed. Slip mode also changes from initially planar-slip to wavy-slip with increasing cycle numbers, which defines the cyclic stress response. Dislocations in veins, walls, labyrinth and cells are found to have different Burgers vectors, suggesting that apart from wavy-slip, multiple-slip also contributes to their formation. Moreover, distinct dislocation substructure in grains is dictated more by the constraints from neighboring grains rather than by their orientation. Additionally, the formation of various dislocation structures in a single grain is also linked to the constraint effects from the neighboring grains.

Cyclic deformation behavior and failure mechanism of S32205 duplex stainless steel under torsional fatigue loadings

Torsional low cycle fatigue tests of ferrite-austenite duplex stainless steel S32205 at various shear strain amplitudes were conducted. The relationship between the evolution of dislocation structures in each constitutive phase and cyclic stress response and cyclic stress-strain curves was thoroughly studied. The surface damage evolution and short cracks nucleation behavior were also discussed. Results show that the cyclic softening occurred at all the strain amplitudes from 0.3% to 1.2% is due to the redistribution and localization of plastic strain and the development of strain transfer between phases, while the formation of regular dislocation cells contributes to achievement of cyclic saturation when the strain amplitude reaches 0.7%. The cyclic stress-strain curves show two-regimes with different cyclic strain hardening rates. As the plastic strain amplitude is smaller than 0.32%, the ferrite and austenite jointly accommodate the plastic strain within material matrix with the coexistence of representative planar slip and incipient wavy slip dislocation configurations in both phases, leading to a low cyclic strain hardening rate. By contrast, the ferrite dominates the plastic deformation with the formation of well-developed low-energy dislocation structures as the plastic strain amplitude is over than 0.32%, resulting in a high cyclic strain hardening rate. Moreover, microstructure observations reveal that the pronounced persistent slip markings in ferrite grains and phase boundaries are the preferential sites for microcrack nucleation and growth.

Microstructure, Thermal Stability during Creep and Fractography Study of Friction-Stir-Processed AA2024-T3 Aluminum Alloy

Friction stir processing (FSP) makes it possible to obtain a stir zone with very fine grain size with the aid of severe plastic deformation. Yet using FSP, it is impossible to obtain a uniform cross section as far as the microstructure and mechanical properties are concerned. To reduce the effect of this limitation, in the current study, the material was processed on both sides, thus yielding a wider, rectangular and more homogenous stir zone. In a recent publication, the authors focused on the mechanical properties, thermal stability and transmission electron microscopy (TEM) study of friction-stir-processed AA2024-T3, comparing this alloy to the parent material. While the previous study mentioned focused on the parent and on the as friction-stir-processed material, the current study focuses on post-creep specimens and hence completes the previous one with microstructural processes occurring during creep. The current paper completes the above precipitate analysis using electron-dispersive x-ray spectroscopy (EDS) mapping of the various precipitates reported after exposure to creep temperatures. The TEM study reported in the current paper revealed the formation of dislocation structures during creep, in parallel to the dynamic recrystallization (DRX) reported by the authors in the past. In addition, fractography study indicated premature cracking as the prevailing failure mechanism as well as in the case of friction stir welded creep specimens.

Fatigue damage assessment of SUS316L using EBSD and PALS measurements

Kernel averaging misorientation (KAM) measurements and positron annihilation lifetime spectroscopy (PALS) were conducted to investigate the damage introduced by the tensile and fatigue testing of type 316L stainless steel. The fatigue tests were carried out at room temperature and at 550 °C under the strain controlled mode with total strain amounts, Δε of 0.4% and 1.5%. A number of different samples were prepared by interrupting the fatigue test at various ratios of fatigue cycle time to fatigue lifetime. Both KAM and PALS analyses indicated increasing damage as increasing misorientation average or number of vacancies with increasing strains in tensile- and fatigue-tested samples. Dislocations play an important role in the evolution of damage as they produce vacancies and form dislocation structures. In the fatigue test at high temperature, accelerated dislocation relaxation encourages formation of dislocation structures that result in an early increase in misorientation. Under the same conditions, the positron lifetime rather decreased because of the migration of defects at early stages of fatigue and rapidly increased at fracture. We observed different responses to mechanical straining that can be useful for evaluation of damage in 316L stainless steel.