High Cycle Fatigue Performance Research Articles

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.

Influence of Alloy 625 Manufacturing Process on 950 °C Oxidation Behavior in Air and Post-oxidation High-Cycle Fatigue Performance

Influence of Alloy 625 Manufacturing Process on 950 °C Oxidation Behavior in Air and Post-oxidation High-Cycle Fatigue Performance

Enhancing high cycle fatigue performance of plasma nitrided AISI 4140 steel by post-aging treatment and direct current magnetic field

Machine elements become unable to perform their duties as a result of fatigue damage. In addition, machine elements that are subjected to fatigue under cyclic loads are exposed to electric and magnetic fields when they are close to electrical and magnetic field sources such as electric motors. Moreover, plasma nitriding is often used to increase the fatigue strength of materials. Although the fatigue properties of surface-treated materials are frequently studied, the fatigue behavior of these materials under a magnetic field is not fully known. Therefore, this study focuses on examining the effects of magnetic field on the fatigue properties of surface-treated materials. For this purpose, AISI 4140 steel samples were plasma nitrided and subsequently post-aged, and then they were tested using a rotating bending fatigue testing system by exposing them to a magnetic field for 30% and 100% of their fatigue life. ε-Fe2-3N and γ’-Fe4N phases were seen in surface-treated samples, in addition to these phases, peaks belonging to the α”-Fe16N2 phase were observed in post-aged samples. Plasma nitriding raised the hardness of the material because of nitride phases and α”-Fe16N2 caused an extra increase. The highest diffusion depth was seen in the post-aged samples because post-aging facilitated the diffusion of nitrogen. Surface treatments increased the fatigue strength of the material. All samples tested under a magnetic field exhibited higher fatigue strength than samples tested without a magnetic field because fatigue crack initiation was prolonged by the magnetic field. Compared to non-magnetic and 30% magnetic samples, the fatigue strengths of the samples in a 100% magnetic field were lower. Furthermore, it was observed that applying a magnetic field had no effect on the samples' fractographic structure.

Effect of the hot forming with synchronous quenching process on high cycle fatigue properties of the 2A97 Al-Li alloy

The 2A97 Al-Li alloys have been used in aircraft to achieve lightweight, its high cycle fatigue performance is one of the important factors that determines aircraft safety. The 2A97-T8 Al-Li alloy is obtained through the 2A97-T3 Al-Li alloy undergoes the hot forming with synchronous quenching process. The 2A97-T3 and 2A97-T8 Al-Li alloys are tested for high cycle fatigue under different stress amplitudes. The fatigue crack propagation path of the 2A97-T3 Al-Li alloy is not only along the direction of maximum shear stress at 45° to the stress direction but also along the direction perpendicular to the stress axis. The fatigue crack propagation path of the 2A97-T8 Al-Li alloy propagates along the direction perpendicular to the stress axis. Under high amplitude stress, the characteristics of quasi-cleavage fracture are found in the fracture morphology of 2A97-T3 Al-Li alloy. However, the characteristics of cleavage fracture are found on the fracture morphology of 2A97-T3 Al-Li alloy under low amplitude stress. Under high amplitude stress, the quasi-cleavage characteristics and the dimples are found on the fracture morphology of 2A97-T8 Al-Li alloy. Under low amplitude stress, the small voids and the dimples are found on the fracture morphology of 2A97-T8 Al-Li alloy. The precipitated phases of the 2A97-T3 Al-Li alloy are multitudinous, fine, and dispersed δ’ phases and a few T1 phases. The precipitates of the 2A97-T8 Al-Li alloy are large, fine, and acicular T1 phases and a few δ’ phases. The hot forming with synchronous quenching process significantly improves the high cycle fatigue properties of the 2A97 Al-Li alloy. In addition, the fatigue cycles, the fatigue life rise and fall plots, the S-N curves, and the fatigue crack growth behaviors of the 2A97-T3 and 2A97-T8 Al-Li alloys are obtained.

Exploring VHCF response in L-PBF AlSi7Mg Alloy: Influence of T6 heat treatment on microstructural characteristics and defect distribution

Laser Powder Bed Fusion (L-PBF) is a popular technique for making intricate parts in various fields. Assessing the load-bearing capacity of components fabricated through L-PBF technique is crucial for broadening their applications across various industrial sectors. While prior research has primarily concentrated on static loads, cyclic loading is critical in real-world engineering applications. The purpose of this study is to investigate the influence of T6 heat treatment on the very high cycle fatigue (VHCF) performance of AlSi7Mg alloy fabricated using L-PBF technique by considering microstructural alteration and defect statistics. This study shows that the investigated heat treatment reduced VHCF response of the alloy. This is attributed to increased hydrogen and oxide porosity in conjunction with their increased diametral sizes along with microstructural alteration. The obtained results bring us closer to better understand and improve the use of the AlSi7Mg alloy in additive manufacturing. This offers a viable option for industries looking to benefit from the advantages of the L-PBF technique for manufacturing components.

Fatigue Behaviors and Dislocation Evolution of Copper and Aluminum Alloy

Face‐centered cubic (FCC) metals are widely used in the field of structural materials due to their excellent mechanical properties, and their fatigue behaviors have always been a focus of attention. Herein, 1060 aluminum alloys with different processing states and copper are selected to study the high cycle fatigue performance at room temperature and high temperature. The fracture morphology and dislocation evolution are characterized through characterization methods such as scanning electron microscope and transmission electron microscope. Based on the research, the main movement mode of dislocations (plane slip or wavy slip) are influenced by stacking fault energy (SFE), which further has a significant impact on fatigue performance. When the SFE of the FCC metal is higher, wavy slip dominates and the material is sensitive to temperature changes; on the contrary, during cyclic loadings, metal with lower SFE is dominated by plane slip, due to the reversibility of plane slip, the damage to the material with low SFE under fatigue loading is more uniform.

High cycle fatigue performance at 650 ℃ and corresponding fracture behaviors of GH4169 joint produced by linear friction welding

GH4169 joints manufactured by Linear Friction Welding (LFW) are subjected to tensile test and stair-case method to evaluate the High Cycle Fatigue (HCF) performance at 650 ℃. The yield and ultimate tensile strengths are 582 MPa and 820 MPa, respectively. The HCF strength of joint reaches 400 MPa, which is slightly lower than that of Base Metal (BM), indicating reliable quality of this type of joint. The microstructure observation results show that all cracks initiate at the inside of specimens and transfer into deeper region with decrease of external stress, and the crack initiation site is related with microhardness of matrix. The Electron Backscattered Diffraction (EBSD) results of the observed regions with different distances to fracture show that plastic deformation plays a key role in HCF, and the Schmid factor of most grains near fracture exceeds 0.4. In addition, the generation of twins plays a vital role in strain concentration release and coordinating plastic deformation among grains.

High-temperature high cycle fatigue performance of laser powder bed fusion fabricated Hastelloy X: Study into the microstructure and oxidation effects

High-temperature fatigue properties are critical for laser powder bed fusion (LPBF) fabricated Nickel-based superalloy Hastelloy-X (HX) used in aero engines. In this study, superior high-temperature high-cycle fatigue properties of LPBF HX were achieved. The detailed investigations show that the grain boundary oxidation promoted by the different deformation modes between neighboring grains, despite the reduced oxygen-related damage in the coarser LPBF HX microstructures, are the potential causes for the inter-granular fatigue crack initiation and the subsequent crack coalescence. In the meantime, the crack propagation could be hindered by the refined carbides and annealing twins with Σ3 misorientation (60°/〈111〉) in LPBF HX. Furthermore, the recrystallized grains formed ahead of the crack tip due to the severe deformation within the plastic zone and high testing temperature have different crystallographic orientations, which leads to the crack propagation path changes and increases the fatigue crack propagation resistance.

Effects of heat treatment and hot isostatic pressing on microstructure and fatigue improvements in Ti-6Al-4V alloy fabricated by selective laser melting

SLM plays a critical role in in-space intelligent manufacturing and defense industries, while inherent hurdles due to internal defects in the SLM parts restrict practical reliability. Post-processing of heat treatment and hot isostatic pressing was comparatively applied to reveal the microstructure and fatigue performance. In this work, the resulted microstructure was revealed by XRD, SEM and TEM. Also, the stress-life curve of high cycle fatigue performance was obtained. This work provides a direct comparison for two post-processing techniques, contributing to more reliable application for SLM Ti alloy industrialization.

Tensile and High Cycle Fatigue Performance at Room and Elevated Temperatures of Laser Powder Bed Fusion Manufactured Hastelloy X.

The application potential of additive manufacturing nickel-based superalloys in aeroengines and gas turbines is extensive, and evaluating their mechanical properties is crucial for promoting the engineering application in load-bearing components. In this study, Hastelloy X alloy was prepared using the laser powder bed fusion process combined with solution heat treatment. The tensile and high cycle fatigue properties were experimentally investigated at room temperature as well as two typical elevated temperatures, 650 °C and 815 °C. It was found that, during elevated-temperature tensile deformation, the alloy exhibits significant serrated flow behavior, primarily observed during the initial stage of plastic deformation at 650 °C but occurring throughout the entire plastic deformation process at 815 °C. Notably, when deformation is small, sawtooth fluctuations are significantly higher at 815 °C compared to 650 °C. Irregular subsurface lack of fusion defects serve as primary sources for fatigue crack initiation in this alloy including both single-source and multi-source initiation mechanisms; moreover, oxidation on fracture surfaces is more prone to occur at elevated temperatures, particularly at 815 °C.

Effect of Force and Heat Coupling on Machined Surface Integrity and Fatigue Performance of Superalloy GH4169 Specimens

GH4169 is one of the key materials used to manufacture high-temperature load-bearing parts for aero-engines, and the surface integrity of these parts in service conditions significantly affects their high-temperature fatigue performance. Under a coupling effect of high temperature and alternating load, the evolution process of the machined surface integrity index of superalloy GH4169 specimens was studied, and fatigue performance tests at 20 °C, 450 °C, and 650 °C were carried out to analyze the primary factors affecting the high-temperature fatigue performance of specimens. The results indicated that the surface roughness of specimens remained essentially unchanged. However, the value of surface residual stress decreased significantly, with a release of more than 60% at the highest temperature. At 650 °C, the surface microhardness increased, while the degree of surface plastic deformation decreased under alternating loads. Simultaneously, when the surface roughness was less than Ra 0.4 μm, surface microhardness was the main factor affecting the high-temperature fatigue performance of specimens. The influence of surface microhardness on low-cycle fatigue performance was not consistent with that on high-cycle fatigue performance. The latter increased monotonically, whereas the former initially increased and then decreased with increasing surface microhardness.

The effect of texture on the very high cycle fatigue performance and deformation mechanism of rolled AZ31B magnesium alloys

AbstractRolling can result in anisotropy in the microstructure and mechanical properties of the sheet material. This study focuses on the very high cycle fatigue (VHCF) performance of magnesium alloys in the rolling direction (RD), normal direction (ND), and the bisecting angle between the ND and RD (ND–RD). The findings reveal that RD specimens demonstrate superior fatigue performance, while the ND specimens exhibit the lowest fatigue resistance. During the crack initiation stage, the primary influential factor is the maximum shear stress. Due to c‐axis alignment with ND direction in grains, the deformation mode for ND and RD specimens primarily involves first‐order pyramidal slip, while ND–RD specimens primarily undergo basal slip and prismatic slip. In early stable crack propagation, grain size and texture cause variations in the morphology of the rough area among the three directional specimens. Notably, the RD specimens show faster crack propagation during crack initiation than early stable propagation stage.

Experimental and numerical study on high-cycle fatigue performance of austenitic stainless steel with pre-charged hydrogen

High-cycle fatigue performance is one of the crucial issues for hydrogen diaphragm compressors, as hydrogen embrittlement affects the components in a high pressure hydrogen environment. In this study, the high-cycle fatigue response of MP7, a novel material of austenitic stainless steel designed for hydrogen diaphragm compressors, is investigated by tests and by numerical ways using the Crystal Plasticity Finite Element Method (CPFEM). The uniaxial tensile tests and fatigue tests are carried out on MP7 specimens with different levels of pre-charged hydrogen. The analysis indicates that, even for MP7 with the improved hydrogen resistance performance, both the ductility and the fatigue limit are still affected by the pre-charged hydrogen in a considerable way. Based on the principles of crystal plasticity theory, a CPFEM model is established and a fatigue life prediction model for austenitic stainless steel with pre-charged hydrogen is proposed. This model successfully predicts the fatigue life under different hydrogen contents and stress amplitudes, and the predicted fatigue lives are well-fitted to S-N curves within a two-fold error band.

Modelling of flexural fatigue behaviours of hybrid engineered cementitious composite link slabs using cycle-driven analysis

Link slabs are designed and expected to be serviced under high-cycle traffic loadings. Although their high-cycle fatigue performance is critical in their practical applications, very few experimental and numerical studies have been conducted to study high-cycle fatigue failure of link slabs due to the huge amount of time and resources needed for fatigue tests and the lack of efficient modelling method for high-cycle fatigue failure. Recently, as a newly developed material with superior mechanical properties, the hybrid fibre reinforced engineered cementitious composite (hybrid ECC) has been recommended for link slab application. In this study, a novel and efficient cycle-driven analysis (CDA) procedure was developed to model the structural behaviour of ECC link slabs made of the hybrid ECC under high-cycle fatigue loadings, which is the first attempt for CDA to be applied in high-cycle fatigue structural modelling of a hybrid ECC link slab with reinforcement bars. In the proposed CDA, fatigue damages of both hybrid ECC and reinforcement bars were taken into account. The accuracy and reliability of the new CDA procedure were validated by comparing the modelling predictions with the experimental results on two quarter-scaled hybrid ECC link slabs. It was found that the proposed CDA procedure could predict the overall fatigue behaviours including the deflection histories, crack patterns, fatigue life, fatigue failure mode and the residual static strength of the hybrid ECC link slabs after fatigue damage with good accuracy.

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.

Effect of surface modification on the high temperature low cycle fatigue performance of LPBF 316L austenitic steel

In this study, high temperature low cycle fatigue (LCF) tests at 550 °C were conducted on LPBF (Laser powder bed fusion) 316L with three different surface states, including the As-built surface (AB), fill contour (FC) manufacturing surface, and the surface combining FC and electropolishing (FC + EP). The effect of surface treatment on the high temperature LCF performance of LPBF 316L was investigated. Experimental results showed that the FC + EP surface treatment had the most significant effect on enhancing life. The difference in enhancing the fatigue life behavior was mainly attributed to the various crack initiation mechanisms with different surface states. The cracks on the surfaces of AB and FC mostly originate from the powder adhesion areas and the boundaries of the melt pool, while FC + EP surface treatment weaken the damage induced by powder adhesion. Furthermore, a parameter representing the fatigue crack propagation driving force that considers the surface condition has been defined, and a proposed life prediction model can provide guidance for surface modification and post-treatment of additive manufacturing materials as well as other metal materials.

A survey of the high-cycle fatigue performance of additively manufactured alloy 718

This paper presents a survey of the published high-cycle fatigue (hcf) data for the nickel–iron superalloy alloy 718 fabricated by additive manufacture. Approximately 680 fatigue data points were collected from the published literature and the reported data are presented in the form of stress versus cycles to failure curves for load ratios of R = −1, 0 and 0.1. Following this, curves showing estimated survival probabilities of 0.5, 0.95 and 0.99 are constructed using a statistical analysis based on the Weibull probability density function. Finally, a comparison between the fatigue performance of additively manufactured and wrought alloy 718 under fully reversed loading conditions ( R = −1) is provided.

On the unusual R-ratio dependence of the high cycle fatigue performance of precipitate strengthened Al alloys

The high cycle fatigue (HCF) performance of precipitate strengthened Al alloys is important for their use in moving structures applications such as transportation. It was first shown in the 1950′s, and has been confirmed multiple times since, that sometimes the weaker underaged alloys can show longer high cycle fatigue lives under R = -1 loading than the stronger peak aged materials. However, under alternative R-ratio loadings (e.g. R = 0.1), the underaged alloys tend to show the same, or even worse, HCF performance as the peak aged alloys. This unusual R-ratio dependence is studied in this work using a combination of fatigue testing on smooth samples, optical profilometry of the evolution of surface roughness during cycling, and transmission electron microscopy.We demonstrate that the unusual R-ratio effect is really an effect of the maximum applied stress, and the critical role that this has in determining the strain localization that occurs during the first cycle of loading. This initial strain localization sets the path for subsequent plasticity accumulation which eventually leads to fatigue failure. The maximum applied stress plays a stronger role in determining the initial strain localization than either the applied stress amplitude or R-ratio and this is the critical factor determining the fatigue life of the precipitate strengthened Al alloys considered in this study.

The effect of κ-carbides on high cycle fatigue behavior of a Fe-Mn-Al-C lightweight steel

Numerous studies have demonstrated the viability of lightweight Fe-Mn-Al-C steels for exhibiting an improved balance of high strength and high ductility in automotive applications. However, their high-cycle fatigue behaviour has been scarcely studied. This work examines the effect of κ-carbides formed during the aging treatment on the high-cycle fatigue performance of an austenitic Fe-29Mn-8.7Al-1C (wt. %) steel. The material is studied in solution-treated, under-aged, and peak-aged conditions. High-cycle fatigue tests and analysis of fatigue fracture surfaces were performed using SEM and EBSD techniques. The results indicate satisfactory high-cycle fatigue performance in the aged material, somewhat better than for high Mn steels. Fatigue crack formation and growth occur predominantly via a quasi-cleavage mechanism along the [1 1 1] crystallographic planes, which is also a plane for planar glide and the formation of persistent slip bands during plastic deformation. The nanoscale intragranular κ-carbides in the aged samples interact with the gliding dislocations, resulting in the shearing of nanoscale κ-carbides in a weakly coupled regime. The resistance of particles to shearing is determined by their size, volume fraction, and antiphase boundary energy (γAPB), which vary during the aging process. The aged Fe-29Mn-8.7Al-1C steel significantly improves the fatigue strength as the formation of persistent slip bands is delayed due to an additional energy barrier related to the shearing of the κ-carbides. This improvement peaks in the under-aged condition and decreases with further aging time.

Enhancing mechanism of TC4 high-cycle fatigue performance by the introduction of hard nitride mono-and multilayer coatings

This paper investigates the enhancement mechanism of mono- and multilayer coatings on the high-cycle fatigue behavior of TC4 under tension–tension. The morphology, phase composition, mechanical properties were measured by scanning electron microscope, X-ray diffractometer and nanoindentation. Electron back scatter diffraction was employed to investigate the fatigue failure mechanism. Median fatigue limits obtained by stair case method of TC4 with TiN coating, TiN/Ti (7:1), TiN/Ti (3:1), and uncoated TC4 after 1 × 107 cycles are 553 MPa, 422 MPa, 480 MPa, and 411 MPa, respectively. Under high-cycle loading, the hard-coating/TC4 substrate experiences fatigue failure through two mechanisms: coating cracking hastens the substrate's fatigue failure, or the fatigue source within the substrate creates sliding steps, ultimately resulting in failure. After 1 × 107 cycles under fatigue strength, the average dislocation density on TC4 as well as coated TC4 is similar. The plastic deformation resistant of TC4 under cyclic load was enhanced with nanoscale hard TiN coatings. This finding underscored that the hard coating significantly improves fatigue resistance by inhibiting crack initiation and accommodating substantial cyclic plastic strain. Furthermore, our research provides strong support for the application of hard ceramic coating on the surface strengthening of titanium alloy.