Fatigue Of Alloy Research Articles

Tibial Baseplate Microstructure Governs High Cycle Fatigue Fracture InVivo.

Previous studies report rare occurrences of tibial baseplate fractures following primary total knee arthroplasty (TKA). However, at a microstructural scale, it remains unclear how fatigue models developed invitro apply to fractures invivo. In this study, we asked: (1) do any clinical factors differentiate fracture patients from a broader revision sample; and (2) invivo, how does microstructure influence fatigue crack propagation? We identified three fractured tibial baseplates from an institutional review board exempt implant retrieval program. Then, for comparison, we collated clinical data from the same database for n = 2120 revision TKA patients with tibial trays. To identify mechanisms, we characterized fracture features using scanning electron and digital optical microscopy. Additionally, we performed cross sectional analysis using focused ion beam milling. The fracture cohort consisted of moderately to very active patients with increased implantation time (15.6 years) compared to the larger revision patient sample (5.1 years, p = 0.009). We did not find a significant difference in patient weight between the two groups (p = 0.98). Macroscopic fracture features aligned well with both previous retrieval analysis and invitro baseplate fatigue tests. On a micron scale, we identified striations on each baseplate, demonstrating fatigue as the fracture mechanism. Invivo fatigue fracture processes depended on both the alloy (Ti-6Al-4V vs. CoCrMo) and the microstructure of the alloy formed during manufacturing. For Ti-6Al-4V, the presence of equiaxed or acicular microstructure influenced the fatigue crack propagation, the latter arising from large prior β grains and a Widmanstatten microstructure, degrading fatigue strength. CoCrMo alloy fatigue cracks propagated linearly, crystallographically influenced by planar slip. However, we did not document any features of overload or fast fracture, suggesting a high cycle, low stress fatigue regime. Ultimately, the crack profiles we present here may provide insight into fatigue fractures of modern tibial baseplates.

Slip transfer and crack initiation at grain and twin boundaries during strain-controlled fatigue of solution-hardened Ni-based alloys

Slip transfer/blocking at grain and twin boundaries as well as preferential fatigue crack nucleation locations were studied in two solution-hardened Ni-based alloys (Inconel 600 and Hastelloy C276) deformed under strain-controlled, fully-reversed cyclic deformation in the low-cycle fatigue regime. Electron backscatter diffraction-based slip trace analysis was used to identify the active slip systems after interrupted fatigue tests. It was found that the Luster-Morris parameter m′=0.6 was an accurate geometrical criteria to discriminate between slip transfer and blocking at grain and twin boundaries. Moreover, it was found that fatigue cracks initiation was always intergranular and cracks were nucleated at grain and twin boundaries when the slip transfer across was blocked. The probability of crack nucleation increased with the misorientation angle and was independent of the grain size. This behavior was associated with the development of stress concentrations at grain and twin boundaries as well as triple junctions in which slip was blocked and is different from previous reports on fatigue crack nucleation in Ni-based superalloys deformed, in which the slip system parallel to the TB in the parent grain was suitably oriented for slip. This contrast in the fatigue crack nucleation sites between both types of Ni alloys were attributed to the differences in the degree of strain localization and show how this factor controls damage nucleation in polycrystals.

Comparative assessment of Ti‐6Al‐4 V titanium alloy fatigue life improvement by vibratory peening, shot peening, and vibratory finishing

AbstractThe effects of vibratory peening (VP), shot peening (SP), and SP followed by vibratory finishing (SPVF) on the surface and fatigue properties of Ti‐6Al‐4 V were compared to conventional low‐stress grinding (LSG). VP processing produced seven times smoother surface finish than SP and 66% deeper compressive residual stresses (CRS) but with 12% lower magnitudes. SPVF produced optimal surface properties with a perfectly flat surface and CRS‐like SP. All three mechanical surface treatments generated similar fatigue life improvements (108–122%) over LSG when the cyclic stress was below the yield stress. Above the yield stress, most of the CRS relaxed during the first cycle in VP specimens, resulting in up to 97% fatigue life improvement over LSG. The CRS relaxed more gradually in SP specimens leading to larger (up to 239%) fatigue life improvement. This shows the need to amplify CRS magnitudes produced in VP to maximize fatigue life improvement.

Wet shot peening effects on surface integrity and very high cycle fatigue of TC17 titanium alloy

With the increasing reliability requirements of aerospace equipment, very high cycle fatigue of TC17 titanium alloy has gained significant attention. This study investigates the effects of different wet shot peening treatments on the surface integrity and very high cycle fatigue performance of TC17 titanium alloy, elucidating the underlying mechanisms. Experimental results show that wet shot peening exacerbates surface defects, increases roughness, creates a plastic deformation layer, and induces compressive residual stress and work hardening. The combined effect of these factors reduces the fatigue performance. However, post-peening polishing significantly enhances the very high cycle fatigue performance by reducing stress concentration from surface defects while retaining the beneficial effects of compressive residual stress. Therefore, polishing after wet shot peening is concluded to be the most effective method for improving the very high cycle fatigue performance of TC17 titanium alloy.

Investigation of micro-mechanisms for facet formation during dwell fatigue in Ti6321 alloy with equiaxed microstructure

Dwell fatigue failure has always been the most concerning threat to titanium alloy components, and the dominant mechanism is still not thoroughly understood. In this work, room temperature stress-controlled dwell fatigue tests were performed on a near α titanium, Ti-6Al-3Nb-2Zr-1Mo alloy with equiaxed microstructure. Quantitative characterization was conducted to reveal the surface morphology and the crystallographic orientation of facets on the fracture. The results shows that faceted primary α grains well aligned with (0001) basal plane. Facets at crack-initiation sites were found with orientation distribution ranging from 20° to 60°, while the facets at crack path shows a more scatter orientation distribution. Based on the results, phenomenological models were proposed to explain the formation of facets from the aspect of slip-assisted cracking, including basal slip band cracking, and mixed-deformation induced cracking, which well elucidated the formation of traditional sharp facet and special step-liked facet morphology.

Dynamic recrystallization mechanisms for improving fatigue life under high temperature low cycle fatigue in FGH95 alloy

High temperature low cycle fatigue (LCF) tests were conducted on the FGH95 nickel-based superalloy at temperatures of 420 °C and 600 °C. The experimental results indicate that the fatigue life of the FGH95 alloy at 600 °C is approximately nine times higher than that at 420 °C under identical stress conditions. This finding differs from the conclusions of previous studies on the effect of temperature on fatigue life. The microstructure of the alloy was characterised, and it was found that there were multiple dynamic recrystallisation (DRX) mechanisms present. Continuous dynamic recrystallisation (CDRX) and discontinuous dynamic recrystallisation (DDRX) were identified as the dominant mechanisms at different temperatures. These different dominant mechanisms contributed to the variation in the fatigue life of the alloys under different temperature conditions at the same stress level.

A micromagnetic-mechanically coupled phase-field model for fracture and fatigue of magnetostrictive alloys

Magnetostrictive alloys are usually brittle materials with micromagnetic structures. Their structural reliability and durability depend on the complex micromagnetic-mechanical coupling at smaller length scales encompassing the evolution of micromagnetic structures. Herein we propose a micromagnetic-mechanically coupled phase-field model for fracture and fatigue behavior of magnetostrictive alloys with evolution of the micromagnetic structure. The thermodynamically-consistent model is derived from microforce theory, laws of thermodynamics, and Coleman–Noll analysis. The evolution of crack phase-field and magnetization-vector order parameters that are fully coupled is governed by history field dependent Allen–Cahn and Landau–Lifshitz–Gilbert equations, respectively. The model is extended to fatigue by introducing a degradation prefactor for the fracture energy as a function of positive elastic energy. One-dimensional analyses are then presented to anatomize the crack driving forces in terms of fully coupled micromagnetic-mechanical and pure mechanical driving force. We demonstrate the model capabilities by finite-element numerical studies on the micromagnetic domain evolution during the crack propagation and the influence of external magnetic field for type-I, type-II, and three-point bending fracture, as well as for the fracture of a single-edge notched specimen with an elliptical inclusion. The simulation result shows that depending on how micromagnetic domains are switched under micromagnetic-mechanical coupling, the magnetic field can enhance or decrease the critical load. In the presence of inclusion with larger fracture toughness, a crack is found to nucleate in the tri-junction of multi-domain micromagnetic structure owing to the high elastic strain around the tri-junction point. It is further found that a suitable magnetic field promoting magnetization-vector rotation around the crack tip could remarkably improve the fracturing load and fatigue life. The results demonstrate the model promising for the study of micromagnetic-mechanically coupled fracture and fatigue in magnetostrictive alloys.

High-temperature thermal fatigue of Ni3Al-based single crystal alloy affected by wall thickness and peak temperature

Complex thin-walled structures are commonly employed in turbine components to improve cooling efficiency. However, thin-walled blades are prone to thermal fatigue failure due to the high thermal stress induced by frequent and abrupt temperature fluctuations during duty cycles. The thermal fatigue behavior of Ni3Al-based single crystal alloy with thin-walled structure during 25 °C ↔ 1000 °C/1100 °C was investigated by combining thermal fatigue tests and finite element simulation. The thermal fatigue demonstrated a significant thickness debit effect, with thermal fatigue property dropping as peak temperature and wall thickness increased. Wall thickness had a more pronounced effect than peak temperature. Visible slip traces were found on the wall thickness surface, and their density was positively correlated with wall thickness. Further investigation revealed that thermal fatigue is primarily driven by the octahedral slip system ({111}<110>), with significant contributions from (111)[101‾] and (1‾1‾1)[101]. Simulations of thermal stress distribution and J-integral at the crack tip during crack initiation and propagation stages indicated that wall thickness influences thermal fatigue properties by affecting thermal stress concentration at the notch and crack tip. Higher peak temperatures increased thermal stress and reduced yield strength, thus diminishing thermal fatigue performance. A thermal fatigue crack propagation prediction model was constructed incorporating Paris' law and the J-integral. The model revealed an unfavorable correlation between material Cj/ nj and both peak temperature/wall thickness, indicating that both factors adversely affect thermal fatigue resistance.

Comparison of Mechanical, Fatigue, and Corrosion Properties of Fusion-Welded High-Strength AA6011 Alloy Using Three Filler Wires

Comparison of Mechanical, Fatigue, and Corrosion Properties of Fusion-Welded High-Strength AA6011 Alloy Using Three Filler Wires

Review on Environmentally Assisted Static and Fatigue Cracking of Al-Mg-Si-(Cu) Alloys

This paper reviews the relevant literature and covers the main aspects of the environmentally assisted cracking of Al-Mg-Si-(Cu) alloys. Apart from a brief overview of the major microstructural and mechanical properties, it presents research results on the corrosion sensitivity and stress corrosion susceptibility of Al-Mg-Si alloys. Possible mechanisms of stress corrosion cracking and corrosion fatigue in aluminum alloys, such as anodic dissolution and/or interaction with hydrogen, are considered. A number of factors, including atmospheric or solution conditions, applied stress, and material properties, can affect these mechanisms, leading to environmentally assisted cracking. Specific attention is given to Al-Mg-Si alloys with copper, which may increase the sensitivity to intergranular corrosion. The susceptibility to both intergranular corrosion and stress corrosion cracking of Cu-containing Al-Mg-Si alloys is mostly associated with a very thin layer (segregation) of Cu on the grain boundaries. However, the effect of Cu on the corrosion fatigue and fatigue crack growth rate of Al-Mg-Si alloys has received limited attention in the literature. At the current state of the research, it has not yet been holistically assessed, although a few studies have shown that a certain content of copper can improve the resistance of aluminum alloys to the environment with regard to corrosion fatigue. Furthermore, considerations of the synergistic actions of various factors remain essential for further studying environmentally assisted cracking phenomena in aluminum alloys.

Cyclic Fatigue of Different Ni-Ti Endodontic Rotary File Alloys: A Comprehensive Review.

Modern endodontics aims to decrease the bacterial load from the complex endodontic space. Over the years, improvements in the operative phases have led to a considerable increase in the success rate of endodontic treatments. The shaping phase has seen the development of new techniques supported by technological innovations that have led to higher treatment predictability. Endodontic instruments have experienced a series of changes that have led to modifications in their design, surface treatments, and heat treatments. The clinical use of rotating nickel-titanium instruments has become widespread and consolidated, a success due primarily to the alloy's mechanical characteristics, which are superior to steel ones, but also to innovations in instrument design. The advent of the Ni-Ti alloy has kept the concepts and requirements of shaping the same but has modified its implementation in endodontics. The following review followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) protocol. The research question focused on Ni-Ti endodontic instruments whose cyclic fatigue was evaluated by analyzing cyclic fatigue strength and the incidence of fracture. At the end of the research, 10 systematic reviews and 1 randomized controlled trial were included in this comprehensive review. The most frequently analysed alloys were M-wire, conventional Ni-Ti, and CM-wire. In seven articles, instruments made of M-wire alloy were used; in eight articles, instruments made of conventional Ni-Ti; and in seven articles, instruments made of CM-wire alloy. The technological evolution of Ni-Ti alloys has led to the development of increasingly high-performance endodontic files that are resistant to cyclic fatigue during clinical practice and have greater resistance to sterilisation practices, making treatment easier and more predictable over time. In particular, heat-treated nickel-titanium root canal instruments present greater resistance to cyclic fatigue than untreated ones and those used with reciprocating kinematics concerning continuous rotation.

Damage accumulation and its effect during thermal- and stress-induced cycling martensite transformation of laser powder bed fused (LPBF) NiTi alloy

Nitinol (NiTi) alloys produced via laser powder bed fusion (LPBF) exhibit promising potential across diverse applications, yet their suitability for devices necessitating repetitive actuation confronts uncertainties regarding microstructural evolution and functional fatigue behavior during cyclic operation. Our investigation unveils that damage accumulation during thermal cycling stems from geometrically necessary dislocations formed through finite-scale incoherent interface motion, contrasting earlier hypotheses attributing LPBF-induced dislocation activity as the primary contributor. Damage accumulation during mechanical cycling is characterized by notable multiplication of cyclic dislocations via dislocation twinning interactions, rather than severe martensitic plasticity. These newborn cycling dislocations inherit martensite's crystallographic characteristics, exerting a distinct influence mechanism on martensite transformation and deformation behavior, diverging from conventional studies on function fatigue in traditional NiTi alloys. This study sheds light on the distinctive damage accumulation traits observed during thermal/mechanical cycling of LPBF-fabricated NiTi alloys, offering valuable insights for probing their functional fatigue mechanisms.

Investigation on high cycle fatigue performance of additively manufactured Alloys: Synergistic effects of surface finishing and Post-Heat treatment

The high-cycle fatigue (HCF) behavior of additively manufactured (AM) materials in structural applications remains insufficiently explored when contrasted with conventionally fabricated alloys. Addressing this research gap, we systematically investigate the potential to enhance HCF performance in AM alloys through a strategic interplay of surface finishing and post-heat treatment design. Concentrating on laser powder bed fusion, we evaluate surface roughness and post-heat treatment effects on HCF life across a300to1000 MPa stress range. Findings show that, at700to1000 MPa, surface finishing significantly extends HCF life by mitigating crack initiation. Paradoxically, at300to700 MPa, it shortens HCF life due to induced local residual stress on the sample surface. Additionally, post-aging finishing moderately enhances HCF life compared to pre-aging. This underscores the crucial role of sequence in surface finishing and heat treatment, emphasizing their collective impact on fatigue properties. Our study advances the understanding of post-processing factors influencing AM alloy fatigue properties, providing valuable insights for enhancing mechanical performance.

A micromechanical view of enhanced reversibility in shape memory alloys

Transformation-induced plasticity (TIP) is the source of poor reversibility and functional fatigue in shape memory alloys (SMA)s undergoing martensitic phase transformation. The TIP is believed to originate from the defect generation at the highly-stressed austenite/martensite transition layer. It is suggested that under satisfaction of compatibility criteria (also known as cofactor conditions) the highly-stressed transition layer is removed and the phase transformation reversibility is highly enhanced. In this study, we employ the inclusion problem of micromechanics along with crystallographic theory of martensite to quantify the generated internal stresses associated with the nucleation of martensite in a wide range of SMAs. The micromechanical calculations show that the nucleation of martensite in SMAs with high degree of compatibility and enhanced reversibility generates much reduced internal stresses. For example, the maximum shear stress generated by nucleation of twinned martensite in Ni50.3Ti29.7Zr20 is ∼ 5 GPa, which is reduced to ∼ 400 MPa (about an order of magnitude reduction) in single-variant martensite of Ni39Ti50Pd11 with excellent reversibility and low functional fatigue. It is also shown that the internal stresses are much lower in a supercompatible twinned martensite microstructure (Cu25Au30Zn45) compared with a conventional twinned microstructure such as those formed in NiTi-based alloys. Analysis of the deformation state of the matrix shows that the underlying mechanism behind the reduced internal stresses is the reduction in the maximum shear strain ((λ3 - λ1)/2) imposed by the nucleation of martensite. The results present a quantified picture of internal (interfacial) stresses in different SMAs to better understand the origin of reversibility and functional fatigue.

Coupling life prediction of bending very high cycle fatigue of completion strings made of different materials using deep wise separable convolution

AbstractThis article predicts bending very high cycle fatigue (VHCF) life of three typical nickel‐based alloys SM2550, BG2532, and G3 used for completion strings. Fatigue tests were conducted on the three alloys using an ultrasonic fatigue system at a frequency of 20 kHz. The results showed that the fatigue strength ranges of the three alloys were markedly different, reflecting their different sensitivities to fatigue loading. Scanning electron microscope observations revealed numerous fatigue crack origins with internal decohesion in the fatigue source region. To achieve unified prediction of the fatigue life for the three alloys, a prediction model based on deep learning was built with inputs including fatigue initiation quantity, cleavage facet size, and other fatigue fracture characteristics. It was found that single source feature was insufficient to obtain satisfactory prediction accuracy for all alloys, while multifeature coupling integration could significantly improve the prediction precision, enabling reliable prediction of alloy fatigue life. This study provides new insights into bending VHCF life prediction.

Assessing and Forecasting Fatigue Strength of Metals and Alloys under Cyclic Loads.

Within the scope of this research, patterns of changes in the fatigue life and limit of metals under cyclic stress were identified and the most informative parameters were determined as the basis for developing a method for the universal transformation of experimental data on the fatigue of metals and alloys for their subsequent generalization. Experimental data on metal fatigue, obtained by a large number of authors for a wide range of grades of steels and alloys, under the influence of various combinations of factors, were systematized. A generalized dependence of the recalculated parameters of fatigue life and limit was obtained, its characteristics were assessed, and a sensitivity analysis was performed, confirming the universal nature of the obtained dependence. A system of parameters has been proposed making it possible to consider and forecast high-cycle fatigue processes for a wide range of metals and alloys, under the conditions of various combinations of operating factors, from unified positions and a more general point of view.

Investigation of neighboring grain effects on load shedding in titanium alloys under cold dwell fatigue

Load shedding under cold dwell fatigue in titanium alloys has been a threat to the safety of the aero-engine since it is responsible for crack formation. The strain incompatibility between the soft-hard grain pair arises from the significant creep in the soft grain during the dwell period, which is fundamentally related to the load shedding. Such deformational heterogeneity is not only affected by the soft-hard grain itself but also by its neighboring grains, but the effect of the latter is rarely reported. In this paper, the effect of neighboring grains, including location, crystal orientation, texture, etc., on load shedding is quantitatively investigated using a three-dimensional rate-dependent crystal plasticity model by controlling the microstructural morphology of the grains. In particular, the mechanism that the dwell fatigue cracks tend to nucleate from the sample's interior rather than the free surface is revealed. Restriction of rigid body rotation from neighboring grains can further enhance load shedding. The crystal orientation of individual and group neighboring grains sitting at different locations with respect to the soft-hard grain pair is evaluated. The grain directly attached to the hard grain has the strongest influence. The statistics of load shedding are analyzed by conducting hundreds of simulations with different textures. Stronger textures are found to be able to enhance load shedding and thus deteriorate the service lifetime. The change of locations showing the highest stress during the dwell period arising from plastic deformation in neighboring grain may lead to the phenomenon of reverse load shedding. Understanding the neighboring grain effects from both the mechanistic basis and the statistical point of view is important in integrity evaluations and service life assessments of titanium components in aero-engines.

Study of superelastic fatigue in Ni-Ti alloy sensors/actuators with shape memory

The fatigue behavior of Ni-Ti springs with shape memory effect, applied in the activation of flow valves was studied. Employing an unconventional method, the structural and phenomenological aspects of the shape memory effect were analyzed. The Ni-Ti alloy was characterized by: Differential Scanning Calorimetry, Optical Microscopy, Scanning Electron Microscopy and Eletron Dispersion Spectroscopy. Subsequently, for the analysis of structural and functional fatigue in shape memory, sensors/actuators in the form of helical springs were submitted to the superelastic fatigue test. The test routine created was performed interspersing slow and fast cycles, controlling temperature, stress and deflection variables. Thus, it was possible to investigate the evolution of critical temperatures, thermoelastic deformations and thermal hysteresis, in specific stages of thermomechanical cycling, to identify a possible degradation of structural and functional properties. It was possible to verify the effectiveness of the proposed methodology in characterizing the Ni-Ti sensor/actuator under the studied conditions.

A new combined impact fatigue damage model and its application of influencing factors analysis on impact fatigue of TC18 titanium alloy

Based on the theory of continuum damage mechanics, a new elastic damage evolution model taking into account the effect of strain hardening is proposed. It is then combined with the previously proposed elastic–plastic damage evolution model considering the strain rate effect to calculate impact fatigue damage evolution and predict fatigue life for specimens undergoing various impact loading conditions. The impact fatigue test was conducted by a hammer impact testing machine and the experimental data was used to verify the proposed damage model. Afterwards, the model was applied to investigate the influences of loading condition, geometric configuration, and specimen size on the impact fatigue damage of TC18 titanium alloy. The calculation results reveal some different characteristics from conventional fatigue. First, the impact energy cannot be regarded as the only index of loading level, because the damage evolution rate increases with the decrease of impact velocity even under the same impact energy. Second, the impact fatigue life becomes longer as the stress concentration coefficient increases under the same loading conditions, which is contrary to the cases of conventional fatigue. Third, the effect of specimen size on impact fatigue life presents a new trend. The larger the specimen size, the shorter the impact fatigue life for notched specimens, while the longer the impact fatigue life for smooth specimens.

Investigation of damage mechanisms in thermomechanical fatigue of nickel-based single-crystal alloys

Thermomechanical fatigue (TMF) is essential for ensuring the safety and efficiency of various thermal engineering systems, however, the underlying damage mechanisms remain unclear. In the present work, a damage evolution model is used to quantify damage mechanisms in nickel-based single-crystal superalloy DD6. The isothermal creep-fatigue model combining the fatigue and creep damages is developed to elucidate their interactions and validated by the tension-dwelling experiments. Finally, the experimentally measured TMF damage is quantitatively decomposed into fatigue, creep and extra TMF components. Significant TMF damage in the in-phase TMF is identified, especially in the [001] specimens, potentially attributed to the non-isothermal creep or oxidation, while damage in out-of-phase TMF aligns with the spiking oxidation mechanism.