High Fatigue Life Research Articles

Mechanical and economical feasibility of LDPE Waste-modified asphalt mixtures: pathway to sustainable road construction

This research study evaluates the impact of low-density polyethylene (LDPE) modified asphalt binder on the mechanical performance and economical feasibility of asphalt concrete (AC) mixtures. LDPE-modified mixtures were compared with conventional mixes prepared with various binders commonly used in India, i.e., VG 30, VG 40, Polymer-Modified Binder (PMB), and Crumb Rubber Modified Binder (CRMB). LDPE-modified mixtures exhibit superior mechanical performance, increasing the stiffness of AC mixtures by 171% and 125% at 25 °C and 35 °C, respectively, compared to VG 30 base binder. Additionally, the indirect tensile strength (ITS) improved by 51% over VG 30. LDPE-modified mixtures also showed improved resistance to permanent deformation, with RTIndex values up to 133.46% higher than VG 30, and higher fatigue resistance, as indicated by increased CTIndex values compared to VG 30 and CRMB. However, the CTIndex values for LDPE-modified mixtures were 26.32% and 56% lower than those for VG 40 and PMB, respectively. Pavement analysis using 3D-Move showed lesser deflections at pavement layer interfaces, resulting in higher rutting and fatigue life for LDPE-modified pavements. Furthermore, LDPE-modified pavements showed up to 57% higher fatigue life (Nf) and up to 42.33% higher rutting life (Nr) than other pavements. The economic analysis showed that the cost of LDPE-modified pavements is comparable to VG 40 and around 10% more economical than pavements containing PMB. Using LDPE also offers environmental benefits by repurposing up to 750 kg for every kilometer of single-lane pavement section having 50mm thick surface course. Overall, LDPE-modified asphalt mixtures present a sustainable and high-performance solution for asphalt pavement construction.

Static analysis of boiler feed pump shaft in steam power plants: Enhancing durability and operational efficiency

Centrifugal pumps are commonly used in industrial and domestic sectors to transport fluids by increasing their flow rate to a specific pressure. One type of centrifugal pump, the Boiler Feed Pump (BFP), plays a crucial role in steam power plants. Designed for continuous operation, BFP shafts are prone to wear and failure due to extreme operational conditions. This study employs computer-aided simulation using SolidWorks software to analyze von Mises stress, displacement, strain, and safety factors of BFP shafts with three material variations: AISI 4140, AISI 316, and AISI 304. The results indicate that AISI 4140 material exhibits the highest safety factor of 2.7 and the lowest displacement of 0.453 mm. Fatigue simulation also shows that AISI 4140 has the lowest damage percentage and the highest fatigue life. These findings suggest that AISI 4140 is the optimal material choice to enhance the durability and efficiency of shafts in applications requiring high reliability, such as BFPs in steam power plants.

Experimental study on low-cycle fatigue performance of high-strength bolted shear connections

In strong earthquakes, low-cycle fatigue fractures may occur in the bolted connections of steel braced frames. Ensuring a high low-cycle fatigue life for high-strength bolted connections is of paramount significance in enhancing the overall safety and collapse resistance of steel structures. Despite substantial research on plate fatigue failure within bolted connections, there remains a research gap regarding low-cycle fatigue failure of high-strength bolts in these connections. This study aims to address the aforementioned shortcomings by conducting 34 sets of low-cycle fatigue tests on high-strength bolted connections. The test specimens all experienced low-cycle shear fatigue fracture at the threaded or unthreaded portion of the bolt shank as the dominant failure mode. Residual deformations were observed in the holes of connection plates. Based on the test data, ultimate shear capacity of a single shear connection is around 0.61Fy (tensile yield bearing capacity of bolt) when the shear force passes through the unthreaded portion and drops to 0.54Fy for the shear force at the thread. The untreated Q355 (minimum yield strength of 355 MPa) steel surface has an average anti-slip coefficient of around 0.37, while milling reduces it to approximately 0.30. The influence patterns of loading amplitude, bolt material, minimum plate thickness, bolt diameter, shear force position and connection type on low-cycle fatigue life are given by range analysis. Among them, variance analysis shows that loading amplitude and bolt material are the primary influencing factors. The correlation coefficient between loading amplitude and low-cycle fatigue life is −0.92, indicating a strong negative correlation. The degradation amount and rate of anti-slip capacity and shear capacity of bolted connections are also investigated. To propose reliable life prediction method, three models were used to establish the relationship between dimensionless shear deformation and low-cycle fatigue life of 10.9-grade high-strength bolted connections. It is not appropriate to use the fatigue categories defined in current standards to predict the low-cycle shear fatigue life of high-strength bolted connections.

High-temperature low-cycle fatigue characteristics of the 12Cr10Co3MoWVNbNB turbine rotor steel

Low-cycle fatigue (LCF) experiments of the 12Cr10Co3MoWVNbNB steel at 598 °C and a strain amplitude ranging from 0.27 % to 0.55 % were executed to reveal the fatigue characteristics, fatigue fracture mechanism, and further to predict the high-temperature fatigue life of the new-style turbine rotor steel. The results indicate that the steel exhibits a high-temperature fatigue softening characteristic. During the high-temperature LCF, the cracks are generated at surface or subsurface defects of the specimens, and the fatigue striations and dimples are apparent on the fracture surfaces of the crack propagation zone and the final fracture zone, respectively. The Smith-Watson-Topper (SWT) and Manson-Coffin models are suitable to predict the high temperature fatigue life of the steel at high/low strain amplitudes, respectively. In terms of finite element analysis of the turbine set rotor, it is determined that the steady state strain of the rotor steel is approximately 0.2 %. And thus, the fatigue life of the steel rotor is estimated as 172,500 cycles at the strain amplitude, based on the Eq. (6) in this work. After 100,000 cycles at the strain amplitude, the yield and tensile strengths of the steel specimens are only reduced by 1 % and 3 %, respectively, indicating a long residual life, which is consistent with the above predicting result.

Relevant Aspects in the Mechanical and Aging Degradation of NiTi Alloy with R-Phase in Endodontic Files.

One of the most important challenges in endodontics is to have files that have excellent flexibility, toughness, and high fatigue life. Superelastic NiTi alloys have been a breakthrough and the new R-phase NiTi alloys promise to further optimize the good properties of NiTi alloys. In this work, two austenitic phase endodontic files with superelastic properties (Protaper and F6) and two austenitic phase files with the R-phase (M-wire and Reciproc) have been studied. The transformation temperatures were studied by calorimetry. Molds reproducing root canals at different angles (30, 45, and 70°) were obtained with cooling and loads simulating those used in the clinic. Mechanical cycles of different files were realized to fracture. Transformation temperatures were determined at different number of cycles. The different files were heat treated at 300 and 500 °C as the aging process, and the transformation temperatures were also determined. Scanning and transmission electron microscopy was used to observe the fractography and precipitates of the files. The results show that files with the R-phase have higher fracture cycles than files with only the austenitic phase. The fracture cycles depend on the angle of insertion in the root canal, with the angle of 70° being the one with the lowest fracture cycles in all cases. The R-Phase transformation increases the energy absorbed by the NiTi to produce the austenitic to R-phase and to produce the martensitic transformation causing the increase in the fracture cycles. Mechanical cycling leads to significant increases in the transformation temperatures Ms and Af as well as Rs and Rf. No changes in the transformation temperatures were observed for aging at 300 °C, but the appearance of Ni4Ti3 precipitates was observed in the aging treatments to the Nickel-rich files that correspond to those with the R transition. These results should be considered by endodontists to optimize the type of files for clinical therapy.

Atomistic insights into friction and wear characteristics of M50 bearing steel: a molecular dynamics simulation study

ABSTRACT M50 bearing steel is a typical alloy material widely used in aeroengines due to its high hardness and fatigue life at high temperatures. To reveal the frictional mechanisms and wear behaviours of contact and sliding, a molecular dynamics simulation model consisting of an indenter and substrate is constructed. The results indicate that, during the indentation process, the normal load exhibits a linear relationship with the indentation depth at shallow depths. With further penetration, the substrate generates severe deformations and subsurface damages. Throughout the scratching process, the average friction force exhibits a linear increase with the growing scratching depth, while the coefficient of friction decreases. Surface morphologies and shear strain distributions are analyzed to elucidate plastic deformation and atomic displacement. Moreover, the wear atom shows a linear proportionality to both scratching distance and depth. These findings enhance understanding of frictional properties and atomic wear behaviour of M50 bearing steel during contact and sliding, potentially informing bearing failure prediction and material optimization.

Comparative Analysis of Concentrically Braced Frames with FeSMA and Steel BRBs Under Long-Duration Earthquakes

ABSTRACT Owing to high fatigue life, the iron-based shape memory alloy (FeSMA) buckling-restrained braces (BRBs) are emerging as a promising candidate against long-duration earthquakes. However, the corresponding analysis cannot be found. Current emphasis is paid on unveiling the seismic response differences between concentrically braced frames (CBFs) with FeSMA and steel BRBs when they are attacked by long-duration earthquakes. To directly assess the effect of earthquake duration, this paper selects a total of 90 pairs of short- and long-duration earthquake records, which are record-to-record spectrally equivalent over a wide range of fundamental periods, for nonlinear time history analysis. A benchmark six-story CBF is selected for demonstration purposes. In the numerical simulation process, the fatigue-induced damage is particularly considered. A preliminary examination is first conducted in the case study, in which a representative pair of short- and long-duration records is selected. In what followed, the statistical results from the ground motion suites are analyzed. This work not only highlights the higher failure risk of steel BRBs than FeSMA BRBs under long-duration earthquakes associated with maximum considered earthquake hazard level, but also confirms the advantages of FeSMA BRBs over steel BRBs in controlling residual deformations.

Effect of post-weld heat treatment methods on microstructure and fatigue behavior of Al-Mg-Si alloy oscillating laser welding

To address the softening issue in aluminum alloy weld joints, post-weld heat treatment(PWHT) techniques were employed to enhance the mechanical properties of Al-Mg-Si alloy weld joints joined by oscillating laser welding(OLW). A systematic investigation was conducted on the impact of two different PWHT methods, artificial aging(AA) and solution treatment followed by aging(STA), on the static mechanical properties, fatigue performance, and microstructure of the weld joints. The results indicated that both AA and STA could improve the tensile strength and fracture strain of the welded joints. Compared to AA, STA did not show a significant improvement in increasing tensile strength and elongation at break. Notably, AA significantly increases the fatigue life of the joints, while STA also contributes to enhanced fatigue life, albeit to a lesser degree. At the lowest stress level, the fatigue life of both STA and as-welded(AW) joints exceeded 106 cycles, with the STA joints exhibiting approximately 57.9% higher fatigue life than the AW joints. Microstructural analysis of the AW joints revealed the presence of dislocations and a few large-sized precipitate phases, primarily Mg2Si and AlFeSi phases. After AA, nano-scale second phases, mainly the AlFeSi phase, appeared in the weld joints, accompanied by a reduction in dislocation density. Following STA, there was a significant increase in the density and size of precipitate phases, with the coarse AlFeSi phase becoming more prominent and large-sized grain boundary precipitates appearing. The AA treatment, due to grain refinement and second phase precipitation, enhanced the hardness, tensile strength, and fatigue strength of the joints. As the STA joints exhibited more β-AlFeSi precipitates and grain boundary precipitates, the second phase strengthening effect was reduced. Although the mechanical properties of STA joints were better than those of AW joints, they were inferior to those of AA joints.

Fatigue response of multiscale extrusion-based additively manufactured acrylonitrile butadiene styrene-graphene nanoplatelets composites

This study investigates the effect of varying concentrations of graphene nanoplatelets (GNPs) on the mechanical and fatigue characteristics of acrylonitrile butadiene styrene (ABS)/GNPs nanocomposites, both in filament form and as 3D-printed parts with different raster orientations. Quasi-static and cyclic loading tests were performed on specimens containing 0.1 wt%, 0.5 wt%, 1.0 wt%, and 2.0 wt% GNPs. The results indicated that the addition of 0.1 wt% GNPs to the ABS polymer matrix increased the ultimate tensile strength (UTS) of the filament by 18 %. Addition of 1.0 wt% and 2.0 wt% GNPs to the matrix improved the Young's modulus of the filament by up to about 35 % but did not enhance the UTS. The filament containing 0.5 wt% GNPs demonstrated the highest fatigue life, even higher than that of the standard samples fabricated through injection molding technique. This was due to its high static strength, Young's modulus, and ductility. However, when the ABS/GNPs nanocomposites were 3D-printed, the addition of GNPs had no major impact on their fatigue life, especially in the higher load levels. Inadequate adhesion and reduced interlayer bonding strength resulted in a detrimental impact on fatigue life of 3D-printed objects. The extrudate-swell phenomenon seems to significantly affect this reduction in fatigue life. To address this, larger nozzle diameter (0.6 mm) was used in fabricating 3D-printed samples. Results indicated that samples with less distortion and smaller extrudate-swell had higher fatigue life. It highlights the importance of considering GNP concentration and printing parameters for optimal fatigue properties in ABS/GNPs composites.

Applicability of normalized resistance rate model for predicting fatigue life and resistance evolution in composite conductive inks

The electrical resistance of metal-polymer conductive inks increases as they undergo cyclic loading, posing a major challenge to their reliability as interconnect materials for flexible electronic devices. To characterize an ink’s fatigue performance, extensive electro-mechanical testing is usually performed. Phenomenological models that can accurately predict the resistance increase with cyclic loading can save time and be useful in flexible conductor design against fatigue failure. One such model was recently developed for only one composite ink type. The model is based on experiments monitoring resistance under monotonic stretch data and multiple experiments measuring the rate of increase of the resistance under different strain amplitudes and mean strains. The current work examines whether such resistance rate model could be generalized to apply for more types of composite inks. Two composite inks with different binder material, metal flake sizes and shapes, and substrate material were experimentally tested under monotonic and cyclic loading. It was found that the two new inks are also more sensitive to strain amplitude than mean strain. The resistance rate model accurately predicts early/catastrophic failure (<1000 cycles) in all inks and conservatively estimates high fatigue life for low strain amplitudes. A protocol detailing the procedures for applying the resistance model to new inks is outlined.

Fatigue properties of riveted joints under different hole perpendicularity errors and squeeze forces.

Riveting is the most important method of joining sheet metal and is widely used in the assembly of aircraft components. The perpendicularity error of the holes is unavoidable during automatic drilling and riveting, which has a significant impact on the quality of the assembly. In this paper, the effects of hole perpendicularity error and squeeze force on the interference fit size, interface contact state, microstructure morphology, fatigue life, and fracture form of riveted joints were investigated experimentally. The results show that the interference fit size increases with a greater tilt angle. When the tilt angle is 0°, the rivet shank is in close contact with the inner and outer sheets, and there is no obvious gap at the interface between the rivet and the sheets. As the tilt angle increases to 2° and 4°, a gap appears at the interface of regions 1, 2, and 3, while the rivet shank at region 4 is in close contact with the outer sheet. The fatigue life decreases when the tilt angle increases from 0° to 4°. For the same tilt angle, the fatigue life of riveted joints with a 0° tilt direction is higher than that of riveted joints with a 180° tilt direction. Increasing the squeeze force can to some extent reduce the adverse effect of the tilt angle on the fatigue life. The hole perpendicularity error does not affect the failure form, while the squeeze force has a significant effect on the failure form of the specimens. RESEARCH HIGHLIGHTS: The fatigue life of riveted joints decreases as the tilt angle increases. The size of the interfacial gap increases with increasing tilt angle. Higher fatigue life at 0° tilt direction than at 180° tilt direction. Increasing the squeeze force can somewhat reduce the negative effect of tilt angle on fatigue life.

A dual cone actuator with high energy density and long fatigue life by developing a nano-silica reinforced dielectric elastomer composite

Dielectric elastomer actuator (DEA) is considered as one of the most promising soft actuators due to its light weight, good flexibility, high actuated strain and energy density. Herein, a novel DEA material is developed by introducing a kind of SiO2 nanoparticles with strong interfacial polarizability into polydimethyl(methylvinyl) siloxane (PMVS). The 7.5 SiO2/PMVS DEA exhibits a high actuated strain of 31.3 % and blocked stress of 68.4 kPa, 2.4 and 2.9 times of pure PMVS DEA. A dual cone DEA (DCDEA) device was self-designed by using 7.5 SiO2/PMVS films, which possesses a high actuated displacement of 1.3 mm, output force of 0.3 N and energy density of 4.7 J/kg. More importantly, because of the high elasticity and strong interfacial interaction, the 7.5 SiO2/PMVS DCDEA exhibits a long fatigue life of 500,000 times, resulting in a full-life energy density of 2.3 × 106 J/kg, 39 times higher than that of the VHB based DCDEA.

A method for manufacturing a mechanically strong and durable hybrid structure of polyethylene–hydroxyapatite composite and titanium alloy

AbstractThe integration of polymer, metal, and ceramic materials in hybrid structures represents a potential but underexplored alternative for biomedical applications. Here, we present a methodology for manufacturing a mechanically strong and durable hybrid overlap structure from a composite of green high‐density polyethylene (HDPE) and hydroxyapatite (HA) compatibilized with HDPE‐g‐MAH joined to a substrate of Ti6Al4V alloy. This process involves laser structuring of micro‐scale grooves on the metal surface, followed by injection overmolding of the polymer composite. A hybrid overlap joint with strong interfacial anchoring was achieved, resulting in outstanding joining strength and fatigue life. This achievement holds significant promise for future biomedical applications.Highlights Joining of composite of HDPE–HA with Ti6Al4V alloy via injection overmolding Laser texturing was effective in improving mechanical interlocking A hybrid joint with high shear strength and fatigue life was developed The hybrid joint is promising for biomedical applications

Microstructure analysis and life prediction of DD6 superalloy under 760 °C combined high and low cycle fatigue conditions

The impact of high and low cycle combined loads on the fatigue performance of DD6 alloy was investigated in this work. Specifically, the combined high- and low-cycle fatigue response of DD6 alloy was examined at a temperature of 760 °C under different low cycle stress amplitudes (960, 1000, and 1040 MPa). The findings revealed that higher low cycle stress amplitudes result in shorter combined high and low cycle fatigue life and less dispersion in life. Correlations between the microstructural features (crystal plane distribution, fracture elevation difference, and the area proportion of crack propagation zone) and fatigue performance were accurately established, demonstrating a linear relationship between these microstructural features and the logarithm of fatigue life. The study also uncovered the evolution rule of microstructural features in high- and low-cycle combined fatigue. Furthermore, the fracture mechanism was analyzed and the distribution of high and low cycle combined fatigue life of DD6 alloy at 760 °C was statistically validated using the dual-parameter Weibull distribution theory. Building upon the crystal plasticity theory, a fatigue life prediction model was developed, and the combined cycle fatigue lifespan under various low cycle stress amplitudes was compared. The comparison between the predicted life and actual fatigue life indicated that the predicted lifespan falls in three times the scatter band.

A Systematic Review of Medium‐Mn Steels with an Assessment of Fatigue Behavior

Deformation‐induced mechanisms, namely, transformation‐induced plasticity (TRIP) and twinning‐induced plasticity (TWIP), are primarily responsible for improved tensile properties in medium‐Mn steels. Additionally, lower density and processing costs make these steels useful in various industries, particularly the automotive industry, which mandates a good understanding of underlying processing–microstructure–property correlations. Therefore, the present study reviews different thermomechanical processes and corresponding microstructural evolutions, followed by mechanical properties. In addition, an assessment of the fatigue behavior of medium‐Mn steels based on duplex or multiphase microstructure and associated mechanisms has been presented. In high‐cycle fatigue (HCF) loading, strain‐induced martensite formation through TRIP at the crack tip is a barrier to dislocation motion. It deviates the crack propagation path to adjacent phases, which results in higher fatigue life. On the other hand, relatively high martensite boundaries initiate microcracks and accelerate crack propagation, resulting in lower life in low‐cycle fatigue (LCF). However, the TWIP mechanism prevents cyclic softening and promotes cyclic saturation, extending fatigue life. The compositions of medium‐Mn steel for enhanced fatigue resistance have been proposed. To that end, it is hypothesized that the TRIP + TWIP mechanisms lead to exceptional LCF performance. Further, microalloyed medium‐Mn steels are expected to exhibit improved LCF and HCF behavior.

Residual stress effect on fatigue behavior of steel welded: A review

A manufacturing process that can be used to join two or more steels by welding. This process involves an uneven distribution of heat which causes residual stresses to occur. Residual stresses in the material, even though the external forces acting have been removed in the local heat distribution area in plastic deformation. Residual stress has a significant relationship with material exhaustion. Tensile residual stress (TRS) can reduce fatigue life, while compressive residual stress (CRS) will increase fatigue life. CRS makes the stress received by the material lower, resulting in a more expansive Fatigue Crack Propagation (FCP) area and a much smaller final fracture cross-section. Materials with CRS have a higher fatigue life than materials without CRS. Fatigue resistance can be increased by reducing the residual stress in tension. Currently one method that is widely used to increase fatigue resistance is shot peening. Shot peening provides CRS on the surface so that crack initiation originates below the surface of the material causing an increase in fatigue resistance.

Fatigue-resistant elastocaloric effect in hypoeutectic TiNi58 alloy with heterogeneous microstructure

Shape memory alloys with high fatigue life and large adiabatic temperature change (ΔTad) are critical for elastocaloric effect in practical solid-state refrigeration applications. Here, we report on the discovery of a hypoeutectic TiNi58 alloy by heterogeneous microstructure design to perform ΔTad of 6.1 K after 2 million fatigue loading-unloading cycles. The fatigue-resistant elastocaloric effect is achieved by a highly reversible quasi-linear superelasticity with strength of 2.2 GPa and modulus of 44.9 GPa. Such stable mechanical behavior is attributed to the prepared unique heterogeneous microstructure, as characterized by multi-scale microscopic analysis. The heterogeneous microstructure is consisted of dendrite regions with Ti2Ni3 precipitates and the surrounding eutectic structure with lath TiNi3 phase. The lath intermetallic TiNi3 phase surrounding dendrite regions works as skeletal reinforcement, providing extra mechanical fatigue stability and giving rise to high strength. The cubic structured Ti2Ni3 precipitates produce local lattice strain due to lattice mismatch within the surrounding B2 matrix with near equiatomic composition. Detailed phase-field simulation based on the local strain field distribution in B2 matrix reveals a continuous transition behavior of martensite under external loads distinct from conventional stress-induced violent autocatalytic martensitic transformation, which is the origin of controlled strain release in quasi-linear superelasticity with ultrahigh fatigue stability. This work demonstrates the potential of hypoeutectic TiNi58 alloy for long-term elastocaloric service and provides guidance to design new elastocaloric materials with high fatigue resistance in bulk mass through simple controlled casting process.

Effect of phase transformation sequence on the low cycle fatigue properties of bainitic/martensitic multiphase steels

The three microstructures of bainite-fresh martensite, pre-martensite-bainite and carbide-free bainite were obtained by modulating the phase transformation sequence by the heat treatment process in the medium-carbon multiphase steel. The effects of martensitic and bainitic phase transformation sequences on the low cycle deformation behavior of multiphase steels were investigated. The results showed that the sample of the fresh martensite transformation process (295 °C–15 min) exhibited the best fatigue life among all processes under strain control. The samples of the preformed martensite transformation process (250 °C–295 °C) and the carbide-free bainite transformation process (295 °C–120 min) exhibited similar fatigue life. The sample of 295 °C–15 min possesses good resistance to plastic destabilization, resulting in higher fatigue life. The results of the EBSD crack propagation path analysis demonstrate that high carbon M/A islands block crack propagation in the sample of 295 °C–15 min, and high angular grain boundaries skew the crack propagation path. Fracture scans observed that secondary cracks in the sample of 250 °C–295 °C extend inward with aggregation of voids, which are more likely to form crack sources.

Largely improved interfacial adhesion and fatigue life of aramid fiber/polymer composites by developing GO enhanced eco-friendly dip-coating system

For achieving high performance and long fatigue life of fiber-reinforced polymer composites (FRPC), a key is to construct strong interfacial bonding between fibers and polymer. Herein, an epoxy resin-based environmentally friendly dipping solution (named as MGL) for aramid fiber (AF) was newly designed and produced to obtain the same good interfacial bonding with natural rubber (NR) as that using traditional toxic resorcinol–formaldehyde-rubber latex (RFL). The H pull-out force and fatigue life of AF/NR composites treated by using the new MGL dipping system are even higher than that using RFL. Based on the theory of interface stress transfer, polyethyleneimine (PEI) modified graphene oxide (GO) was further introduced into the new dipping system, and the H pull-out force, 180° peel-out force and fatigue life of AF/NR composites largely increase by 23.8%, 26.7% and 60.7%, respectively. The H pull-out force of AF/NR composites is significantly higher than that reported in previous studies.

Improvement of low-cycle fatigue behavior of modified 9Cr-1Mo steels at 450 °C in liquid LBE environment by the addition of Si element

This study examined the low-cycle fatigue performance of two modified 9Cr-1Mo steels containing Si at levels of 0.38% and 1.2%, respectively. The investigation was conducted under conditions of 450 °C oxygen-saturated and oxygen-poor lead–bismuth. The elevated oxidative corrosion behavior at this temperature aligns more closely with operational conditions. Comparing the steels with differing Si contents offers a clearer insight into the impact of Si element incorporation on the material's mechanical properties. The results indicated that the high-Si steels had a higher fatigue life, and their fatigue fractures exhibited quasi-dissociation. The high-Si steel displayed elevated oxidation resistance, as indicated by the slower growth of the oxide layer. Owing to significant oxidative corrosion, the fatigue life of the low-Si steel was shorter in oxygen- saturated LBE compared to oxygen-poor LBE. The LME-induced cracking of modified T91 steel in LBE initiated at the grain boundaries. During the expansion phase, a blend of ductile and brittle behaviors was observed, occurring through and alongside grain expansion patterns. Due to the elevated Si elemental content, high-Si steel exhibited weakened susceptibility to LME in oxygen-saturated LBE, owing to the creation of SiO2 through the reaction between Si and dissolved oxygen in the LBE, which shielded the steel matrix.