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The development of automated segmentation and quantitative characterization of microtextured regions (MTRs) from the complex heterogeneous microstructures is urgently needed, since MTRs have been proven to be the critical issue that dominates the dwell-fatigue performance of aerospace components. In addition, MTRs in Ti alloys have similarities to microstructures encountered in other materials, including minerals and biomaterials. Meanwhile, machine learning (ML) offers new opportunities. This paper addresses segmentation and quantitative characterization of MTRs, where an ML approach, the Gaussian mixture models (GMMs) coupled with density-based spatial clustering of applications with noise (DBSCAN) clustering algorithms, was employed in order to process the orientation data acquired via EBSD in the Matlab environment. Pixels with orientation information acquired through electron backscatter diffraction (EBSD) are divided and colored into several "classes" (MTRs) within the defined c-axis misorientations (i.e., 25°, 20°, 15°, 10°, and 5°), the precision and efficacy of which are verified by the morphology and pole figure of the segmented MTR. An appropriate range of c-axis misorientations for MTR segmentation was derived, i.e., 15~20°. The contribution of this innovative technique is compared with previous studies. At the same time, the MTRs were statistically characterized in the global region. [ABSTRACT FROM AUTHOR]

The development of automated segmentation and quantitative characterization of microtextured regions (MTRs) from the complex heterogeneous microstructures is urgently needed, since MTRs have been proven to be the critical issue that dominates the dwell-fatigue performance of aerospace components. In addition, MTRs in Ti alloys have similarities to microstructures encountered in other materials, including minerals and biomaterials. Meanwhile, machine learning (ML) offers new opportunities. This paper addresses segmentation and quantitative characterization of MTRs, where an ML approach, the Gaussian mixture models (GMMs) coupled with density-based spatial clustering of applications with noise (DBSCAN) clustering algorithms, was employed in order to process the orientation data acquired via EBSD in the Matlab environment. Pixels with orientation information acquired through electron backscatter diffraction (EBSD) are divided and colored into several “classes” (MTRs) within the defined c-axis misorientations (i.e., 25°, 20°, 15°, 10°, and 5°), the precision and efficacy of which are verified by the morphology and pole figure of the segmented MTR. An appropriate range of c-axis misorientations for MTR segmentation was derived, i.e., 15~20°. The contribution of this innovative technique is compared with previous studies. At the same time, the MTRs were statistically characterized in the global region.

The present work deals with revealing the fatigue and dwell-fatigue behavior and correlated damage mechanisms of Fe–Mn–Al–C lightweight steel. Surprisingly, alteration in loading mode from monotonic to cyclic induces reversible dislocation movement and facilitates the occurrence of dynamic strain aging. Additionally, applying dwell time by an acceleration of strain aging intensified stress asymmetry during dwell fatigue. The occurrence of strain aging has a bilateral effect on the crack initiation and growth. On one hand, strain aging stimulates twin formation and retards fatigue crack initiation, however, on the other hand, reduces hardening capacity, restricts the plastic deformation and facilitates crack propagation.

This paper investigated the crack initiation and propagation behaviour of Ti-6Al-4V-0.55Fe alloy under the low-cycle dwell-fatigue. It found that cracks were preferred to initiate at the α/β-phase boundaries, the α/α-phase boundaries, and the twinning boundaries within the α-phase. Twinning played a key role in the crack initiation, for the reason that it changed the phase orientation on its sides. Besides, grain orientation was another important factor in the crack nucleation. The soft/hard grain boundaries may become the crack nucleation sites due to the dislocation pile-up. In addition, as the dwell time increased, the fraction of the high Schmid factor of prismatic slip was increasing, which resulted in more cracks. Furthermore, the fracture mode of the alloy was intergranular fracture with microporous aggregation. [ABSTRACT FROM AUTHOR]

This study investigates the slip system activities in primary α grains of a forged Ti–6Al–4V alloy under pure fatigue and dwell-fatigue conditions, using high-resolution digital image correlation (HR-DIC) analysis obtained through interrupted mechanical tests. A quantitative examination of operating slip systems and strain localization on large-field HR-DIC data is conducted using an automated analysis framework developed in a previous study. The findings reveal higher slip activities under dwell-fatigue conditions, evidenced by parameters such as slip band density, area fraction of grains activated with slips, and mean equivalent plastic strain intensities along slip bands through statistically sound analysis. A notable shift in dominant slip activity from basal slips to prismatic slips is observed under pure fatigue conditions, while dominant prismatic slip activity persists throughout dwell-fatigue processes. Furthermore, slip bands with early-developed high strain localization, referred to as slip markings, are identified as prerequisites for surface crack initiation, and three types of slip markings are discovered. Finally, possible reasons for dwell-life debits, and potential anisotropy in the two major slip systems, basal and prismatic slips, are discussed. • Slip system activities are analyzed for bimodal Ti–6Al–4V under pure fatigue and dwell-fatigue conditions. • Quantitative analysis on slip band activities is obtained through large-field HR-DIC data. • Similarities and differences in slip band activities are identified for different conditions. • Cracks are observed on slip band with early developed high strain localization in dwell-fatigue. • Anisotropic slip behaviors between basal and prismatic slips are discovered. [ABSTRACT FROM AUTHOR]

In the present study, the mechanism of fatigue and dwell-fatigue crack initiation was investigated in Ti-6Al-4V with a bi-modal microstructure. While substantial dwell-fatigue life debit was evidenced, microstructural configurations associated with crack nucleation are similar and suggest a unique mechanism for fatigue and dwell-fatigue loadings. Pairs of α grains well oriented for basal slip and separated by a (0001) twist grain boundary were found to be critical configurations for crack initiation. Intense slip is localized at the boundary and precedes crack formation along this boundary. Data from a prior fatigue study was revisited and supports the occurrence of this mechanism. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The prior studies have investigated the influence of internal hydrogen on dwell-fatigue behavior of near- α titanium alloys primarily in the lamellar microstructural condition. In the current study, the effects of internal hydrogen, in the range 10–230 ppm (by weight), on the dwell-fatigue behavior of Ti-6242Si alloy were investigated. The examined alloy had a bimodal microstructure comprising approximately 70 vol% primary α grains and 30 vol% transformed β regions. The dwell-fatigue life generally increased with increasing hydrogen content. The dwell-fatigue lives were longer by a factor of as high as 6 for high (≥150 ppm) hydrogen contents than for the low (<60 ppm) hydrogen contents, which is reported for a near- α titanium alloy for the first time. The crack-initiation site was essentially faceted for all the hydrogen levels examined in current study. The crystallographic orientations of fracture facets at the crack-initiation sites were similar for the low (<60 ppm) and high (>150 ppm) hydrogen contents. Specifically, these facets were inclined at ∼8 – 17° from the basal plane. Therefore, the longer dwell-fatigue lives observed for the alloys with hydrogen contents ≥150 ppm could not be explained on the basis of any differences in crystallography of the facets at crack-initiation sites. The longer dwell-fatigue lives for higher hydrogen contents can be explained within the framework of time-dependent load shedding from the soft microtextured regions (MTRs) to the hard MTRs if the local stress redistribution at the soft MTR/hard MTR boundary due to the hold at maximum load is reduced with increasing hydrogen content. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Ti-6Al-4V alloy is widely used for the deep-sea manned submersible. In addition to the normal cyclic loading, the manned cabin will experience a period of dwell time in each cycle during their service life. In this research, the fatigue and dwell-fatigue crack growth behavior of Ti-6Al-4V alloy under different dwell time were studied experimentally. The mechanism of dwell-fatigue crack growth was investigated. The acceleration phenomenon of the dwell-fatigue crack growth can be directly observed in the experiment. The relationship between the crack length and the dwell time was captured under different Δ K within one cycle. The results presented that there is a saturation time for the dwell-fatigue crack growth. A prediction model is proposed to predict the dwell-fatigue crack growth behavior considering the effects of dwell time. [ABSTRACT FROM AUTHOR]

• Macrozones lead to a reduction in fatigue and dwell-fatigue lifetimes in Ti-6Al-4V. • The competition between fatigue and dwell-fatigue fracture mechanisms was studied. • Dwell-time makes macrozones with different orientations critical. • Main cracks nucleated at basal twist grain boundaries for all conditions. • A weak microtexture inhibits the rapid growth of small dwell-fatigue cracks. The influence of microtexture on the fatigue and dwell-fatigue response of Ti-6Al-4V was investigated considering two regions of a part showing different degrees of microtexture. A high degree of microtexture resulted in a significant reduction in fatigue lifetime. No difference in crack initiation mechanism was observed, as main cracks formed along basal twist grain boundaries (BTGB) connected to the specimen surface. However, a key contribution of faster small crack growth in the strongly microtextured region is suggested. A 120 s dwell time resulted in a dwell-fatigue lifetime debit exceeding a factor of 10 in this region while it remained below a factor of 3 in the weakly microtextured region. In the dwell-sensitive region, internal nucleation of the main crack occurred at a BTGB and long range facetted growth was enabled by the adjacent microtextured region with a dominant [0001] orientation. In contrast, surface crack nucleation typical of fatigue failures dominated in the dwell-insensitive region. The limited growth of internal cracks suggests that the lack of path for rapid crack growth has a pivotal effect for the low dwell sensitivity. The competition between fatigue and dwell-fatigue damage highlights the importance of considering both in modeling approaches to obtain accurate lifetime predictions. [ABSTRACT FROM AUTHOR]

• Low cycle and dwell fatigue response of SLM Ti6Al4V alloy were investigated. • Cyclic softening was more dominant during cyclic loading than the dwell one. • Dwell load reduced the fatigue lives due to redistributed and relaxed stresses. • Life-debit was more at low strain amplitudes due to cumulative damage during dwell. • Dwell fatigue damage was associated with the multiple crack initiation sites. The Ti6Al4V is a cold dwell sensitive alloy, as evident from the failure investigations of several aerospace fan discs and past laboratory research data. However, the studies on the dwell-fatigue sensitivity of additively manufactured Ti6Al4V alloy and its underlying failure mechanism at room temperature are limited. In this study, the cyclic plasticity behavior and the cold dwell sensitivity of powder-bed fusion based additively manufactured Ti6Al4V alloy has been investigated. The standard test specimens of Ti-alloy were fabricated using the selective laser melting process and were subjected to the low cycle fatigue and low cycle dwell fatigue tests, at the same strain rate. A significant reduction in the fatigue lives of specimens exposed to a dwell period was observed at relatively lower strain amplitudes, while fatigue lives were nearly the same at higher ones. The fractographic analysis of the broken specimens revealed multiple crack initiation regions under the action of dwell loadings. The cracks were initiated either from the process-induced defects or by the mechanism of facet formation in the α laths. The failure mechanism based on stress redistribution and its relaxation are discussed to explain the observed results and are presented in this study. [ABSTRACT FROM AUTHOR]

The introduction of welded assemblies in aerospace components aid in weight reduction, but also lead to an increased risk of defects. It is therefore important to analyze the high temperature crack growth resistance of such welds. The results from high temperature cyclic and dwell-fatigue testing of surface flawed Alloy 718 welds are presented here. An increasing temperature and application of a dwell time accelerate the crack growth and increase interaction with secondary phases. During cyclic loading at 550 °C, there is little interaction with the microstructure during transgranular propagation, but the application of dwell times results in a mixture of transgranular propagation and intergranular cracking of boundaries between different dendrites. At 650 °C, mixed intergranular and transgranular mode of crack growth is seen under both cyclic and dwell conditions. However, during dwell-fatigue the interfaces between the secondary arms of the same dendrite are also weakened, leading to an interfacial type of crack growth also in the intergranular parts. [ABSTRACT FROM AUTHOR]

Although Ti-6Al-4V is the most commonly used titanium alloy in the aerospace industry, the mechanisms governing crack initiation in the different fatigue regimes are not well understood yet. This situation partly pertains to a competition between multiple crack initiation mechanisms. In particular, applied loading conditions were identified as a key parameter governing the transition between mechanisms. The fatigue behavior of Ti-6Al-4V with a bi-modal microstructure was investigated in the present study using different waveforms, load ratios and frequencies to clarify this feature. A detailed characterization of the main crack initiation sites was carried out to identify microstructural configurations governing crack nucleation in low-cycle dwell-fatigue, low-cycle fatigue and high-cycle fatigue regimes. While lifetimes and fracture surfaces showed a good consistency with data from prior studies, a single microstructural configuration was found involved with the formation of crack initiation facets. All investigated cracks leading to specimen failure were nucleated along (0001) twist grain boundaries exhibiting similar features. Based on this finding, a criterion is proposed to identify candidates for crack initiation. This also demonstrates no major sensitivity of the critical microstructural configurations to environment, free surface, loading conditions and, as shown in previous studies, microstructure and composition. However, conventional fatigue failure results from one, or a few, surface or subsurface crack initiation sites while dwell-fatigue failure involves the formation of multiple internal cracks. This is accompanied by a significant dwell-fatigue life debit at peak stress magnitudes close to the yield strength. Features of microstructural configurations prone to crack nucleation are finally compared with data reported in existing literature to propose a mechanism of crack formation in Ti alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, the fatigue behaviors of a nickel-based superalloy FGH96 with different microstructural morphologies generated from different heat-treatment processes were investigated. The fatigue and dwell-fatigue tests with the same maximum stress of 1200 MPa were conducted at 650 °C. The relationship between the γ' morphology and the fatigue properties was established. The results indicate that the critical shearing stress of dislocation movement played a key role in affecting fatigue life. No apparent difference can be observed from the fracture morphology at the macroscopic scale for normal fatigue and dwell-fatigue tests. However, in the crack initiation region, the crack was observed to grow along the grain boundary for the dwell-fatigue condition, resulting in the intergranular fracture, similar to creep failure. The introduction of dwell time in the fatigue loading brings larger cyclic strain deformation originates from massive dislocation slip. The dwell debit for the considered loading condition is about 100 times. • The size of γ′ precipitate played a key role in determining fatigue and dwell-fatigue life. • When the applied stress is 1200 MPa and the dwell time is 2 min, the dwell debit is about 100 times. • Dwell time brings the larger cyclic strain deformation and significant damage to the service life. • The fracture morphology of dwell-fatigue combines the characters of both fatigue and creep. [ABSTRACT FROM AUTHOR]

The elastoviscoplastic behavior of α Ti-alloys microstructures is simulated under dwell-fatigue loading in order to identify the favorable crack initiation sites. To aim this goal, a mathematical model is developed using Cellular Automata (CA) approach. Each α Ti-alloy microstructure is presented with a Cellular Automaton formed of 900 and 10,000 cells where each cell represents a hexagonal close packed (HCP) grain of a polycrystalline microstructure. In order to describe a non-textured microstructure, each cell was associated with a randomly distributed crystallographic orientation. The medium in the CA model was built using the six first-degree neighbor cells. Each cycle of dwell-fatigue loading is simulated by three steps: load, creep and unload using the averaged stress–strain fields in all cells. An adapted elastoplastic Eshelby localization approach is used to reach the local strains and stresses in each cell. The elastoplastic behavior of cells during the load step is simulated using a linear isotropic hardening model while a time dependent elastoviscoplastic model is used for the simulation of the cells’ behavior during the creep step. The unload step is assumed to be elastic and residual stresses were calculated at the end of each load cycle and stored for the next cycle. Simulations were run for 3000 dwell-fatigue cycles on three different non-textured microstructures. Stress–strain fields at macro/microscopic scales dwell time effect and critical cells which can be favorable for crack initiation were investigated. The results obtained by the CA model are in accordance with experimental observations found in the literature in terms of stress–strain distributions, crack initiation sites, dwell time effect and the effect of microstructures dispersion. Distribution of residual stresses and neighbors’ effects are finally investigated and discussed. [ABSTRACT FROM AUTHOR]

The deep-sea manned cabin endures dwell-fatigue loading process during service. The high strength titanium alloy Ti–6Al–4V ELI adopted for the manufacture manned cabin is of creep nature in the room temperature. So the dwell-fatigue property of this material should be evaluated for service life estimation. This paper presents the experimental research results on dwell-fatigue property of Ti–6Al–4V ELI. The strain accumulations under different loading conditions are reported. Results show that the strain accumulation behavior of the material under dwell-fatigue loading conditions are very similar to that under the condition of normal creep with three stages; and the increase in total strain with respect to number of cycles was much more pronounced for specimen at higher stress level, while the dwell time will affect strain accumulation when it is plotted versus cycles while strain accumulation tends to be similar in the abscissa of time for different dwell time under test. Based on the results, a dwell-fatigue life curve is derived based on the analysis, which can be applied in the material evaluation and service life estimation of the manned cabin. [ABSTRACT FROM AUTHOR]

• Effects of loading conditions on life distribution are explored by using CPFE. • GND density is predicted to understand dwell-fatigue damage mechanism. • Accurate life prediction under wide loading conditions is presented. • 3-D tolerated damage diagram is developed for residual dwell-fatigue life. In this work, a dislocation-based crystal plasticity finite element (CPFE) framework was implemented to investigate the effects of loading conditions on dwell-fatigue crack initiation life. Experimentally, a large number of strain-controlled dwell-fatigue tests were carried out at 650 °C in a nickel-based superalloy. The combinations of CPFE simulations and post-test examinations were used to reveal the dwell-fatigue crack initiation mechanisms. Then, a life prediction approach was presented on the basis of accumulated energy dissipation at half-life cycle. Good agreement between the experimental and simulated lives verifies the robustness as well as the accuracy of the present approach. Finally, a new three-dimensional (3-D) damage tolerance diagram was proposed by introducing a CP-based physical parameter to describe the degradation levels and evaluate the residual dwell-fatigue life. [ABSTRACT FROM AUTHOR]

• The small fatigue crack growth (CG) was monitored in Ti alloys. • CG was faster in equiaxed α than in transformed β. • Well aligned basal planes with high Schmid factors lead to highest CG rates. • Load holds induced an substantial crack acceleration. Microstructurally small crack growth was monitored in Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo with equiaxed and bi-modal microstructures. The influence of the microstructure was assessed to obtain an improved understanding of the lifetime variability observed in Ti alloys. Primary α grains, basal plane cracking and misalignment across boundaries were identified as key features for high crack growth rates. The origin of life debits encountered under dwell-fatigue loadings was also investigated through crack growth monitoring with the introduction of load holds at peaks stress. Dwell periods were found to induce a substantial small crack acceleration. [ABSTRACT FROM AUTHOR]

Abstract: Cellular automata were used to simulate microstructure heterogeneities at local (one grain) and global (aggregate of grains) levels in an attempt to better understand the large discrepancies observed between fatigue and dwell-fatigue behaviors of some titanium alloys. Eshelby theory was used to estimate the local stresses and strains developed in the microstructure. In the case of simple fatigue tests, loading and unloading stages were used to calculate and describe the strain accumulation history. For dwell fatigue analysis, a thirty second steady state at maximum load was applied to simulate the dwell period. In the present study, the local stress, strain and creep rate in each grain are calculated as a function of the mechanical properties of the neighboring grains. The data are then compiled and the overall behavior of the aggregate is predicted. The results can reproduce and explain some specific features observed experimentally in fatigue and dwell-fatigue tests of near alpha titanium alloys. [Copyright &y& Elsevier]

Abstract: This work assesses the residual stress relaxation of the nickel-based alloy RR1000 due to thermal exposure and dwell-fatigue loading. A number of different characterization methods, including X-ray residual stress analysis, electron back-scattered diffraction, microhardness testing and focused ion beam secondary electron imaging, contributed to a detailed study of the shot-peened region. Thermal exposure at 700°C resulted in a large reduction in the residual stresses and work-hardening effects in the alloy, but the subsurface remained in a beneficial compressive state. Oxidizing environments caused recrystallization in the near surface, but did not affect the residual stress-relaxation behaviour. Dwell-fatigue loading caused the residual stresses to return to approximately zero at nearly all depths. This work forms part of an ongoing investigation to determine the effects of shot-peening in this alloy with the motivation to improve the fatigue and oxidation resistance at 700°C. [Copyright &y& Elsevier]

Fatigue crack growth rate (FCGR) tests with different load ratios and dwell-fatigue crack growth rate (DFCGR) tests with different dwell times were conducted at 750°C for Incoloy 800H. As the load ratio increases from 0.1 to 0.5, the crack growth rate increased and the transition ΔK value from region I to region II (Paris regime) shifted leftward. In DFCGR tests with dwell time of 10 and 30 seconds, the Paris regime started at relatively lower ΔK level and the crack grew much faster than in FCGR tests. However, the crack growth rates between the 10 sec and 30 sec dwell times were relatively similar. The higher crack growth rates in the DFCGR tests compared to FCGR tests was associated with the reduction of the MC precipitates in the vicinity of the advancing crack by the Cr depletion, suggesting the crack propagation in DFCGR conditions was environmentally assisted. The crack growth rate was controlled by trans-granular mode regardless of the dwell time because the dwell time was not enough to cause creep damage. [ABSTRACT FROM AUTHOR]

Abstract: In β-forged Ti6242, dwell periods during ambient stress-controlled fatigue substantially reduce the lifetime. Cracks initiate due to the coalescence of shear-induced cavities nucleated at α/β interfaces. This damage is most often due to pyramidal slip and enhanced by dwell periods. The influence of the hydrogen content on the tensile, creep and fatigue behaviour, damage mechanisms, and crack growth was investigated. Hydrogen reduced the proportional limit and the serrations on the tensile curves but increased the conventional yield stress at high strain rate, so that it either slowed down or enhanced room temperature creep, depending on the applied stress. When a H-induced reduction in creep occurred, H had a beneficial influence on the fatigue and dwell-fatigue lives, in spite of an acceleration of fatigue crack growth. Observations of the H distribution, using the microprint technique show that even though most of it resides in the β phase, some is transported into the α phase, especially in heavily deformed α laths. [Copyright &y& Elsevier]

This paper presents the results of a combined experimental and analytical study of fatigue crack growth and dwell-fatigue crack growth in forged Ti–6Al–2Sn–4Zr–2Mo–0.2%Si (Ti-6242). Following an initial characterization of microstructures and basic mechanical properties, the micromechanisms of long fatigue crack growth are presented for three microstructures. These include: a duplex α/β structure, an elongated α/β structure, and a colony α/β microstructure. The colony microstructure is shown to have the best resistance to fatigue crack growth. The elongated α structure has intermediate resistance, while the equiaxed α structure exhibits the fastest fatigue crack growth rates. The fatigue crack growth rates in the near-threshold, Paris and high ΔK regimes are then characterized with empirical crack growth laws that relate the crack growth rates to the stress intensity factor range and key parameters on the fatigue crack growth curve. Finally, the results of dwell-fatigue crack growth experiments are presented for the three microstructures. The dwell-fatigue crack growth rates are shown to be almost identical to the fatigue crack growth rates in the intermediate ΔK regime. However, the fatigue crack growth rates are faster at higher stress intensity factor ranges. The underlying mechanisms of dwell crack growth are compared with the mechanisms of fatigue crack growth before discussing the implications of the work for the prediction of dwell or fatigue crack growth in Ti-6242. The effects of cyclic frequency on fatigue crack growth are also explored. [Copyright &y& Elsevier]

The charm of diffusion coatings is mainly in their protective function of the surface of gas turbine components, which are often subjected to fatigue-creep loading in extremely hostile environments. Their impact gains in importance with the increasing time that the components are exposed to high temperatures and aggressive environments. This motivates the authors to study the low cycle fatigue behaviour of Al-Cr coated nickel-based superalloy Inconel 713LC. Polycrystalline diffusion Al-Cr coating was produced by out-of-pack Cr-modified aluminising chemical vapour deposition technique on the surface of cylindrical fatigue specimens manufactured by investment casting. Continuous low cycle fatigue (CLCF) tests and dwell-fatigue (DF) tests where a 10-minute tensile dwell was included in each cycle were conducted in strain control mode with constant total strain amplitude at 800 °C. The fatigue behaviour was characterised by cyclic hardening/softening curves, cyclic stress-strain curves and fatigue life curves. The Al-Cr coating provided excellent protection against surface oxidation of Inconel 713LC, especially during dwell-fatigue tests. The substrate as well as the Al-Cr coating were examined in as-coated conditions and after fatigue loading through scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX). Dislocation arrangement in the substrate material was investigated in a transmission electron microscope (TEM). The microstructural observations and the discussion on the degradation mechanisms of surface-treated superalloy have been provided for both regimes of cycling. • Aluminide coating was deposited on Ni 3 Al based alloy using the out-of-pack CVD. • High temperature fatigue and dwell-fatigue tests at 800 °C were performed. • The potential of Al-Cr coating to increase fatigue life was presented. • The damage mechanism of fatigue and dwell-fatigue loading was discussed. [ABSTRACT FROM AUTHOR]

• Deformation mechanisms were analyzed for fatigue and dwell-fatigue tested Ti-6Al-4V. • < a >-type slip, < c + a >-type slip, twinning and interface sliding were found active. • Conditions associated with the different deformation mechanisms were identified. • The loading conditions significantly influence the operating deformation processes. This paper investigates the deformation processes operating in α grains of Ti-6Al-4V submitted to fatigue and dwell-fatigue loadings at room temperature. With this aim, mechanical tests were interrupted after a given number of cycles or cumulated plastic strain. Slip traces analysis combined with electron back-scattered diffraction enabled to evidence the operation of and slip, twinning and interface sliding. The main parameters controlling their activity were analyzed, in particular regarding the crystallographic orientation and the load hold duration. Based on this statistically sound investigation, the differences between fatigue and dwell-fatigue behaviors are finally discussed. [ABSTRACT FROM AUTHOR]