High Temperature Fatigue Research Articles

О живучести жаропрочного никелевого сплава ЭИ607А при длительной эксплуатации

The regularities of high-temperature fatigue in heat-resistant nickel alloy EI607A under full-time conditions (for 22 773, 25 778, 80 000, 95 223, 105 227, 109 594 hours) have been investigated. The regularities of material degradation with increasing service life, accompanied by the occurrence of heterogeneity in the distribution of microhardness, the manifestation of the hardening and softening effects in the thermally loaded zone, as well as microbrittleness, which contribute to reducing the survivability of the alloy, were established.

Effect of high-temperature thermal fatigue on mode I fracture toughness of gabbro

Investigating variations of rock fracture toughness after high-temperature thermal fatigue is greatly significant for developing deep geothermal resources. This study investigated the mode I fracture toughness of gabbro after high-temperature fatigue treatment by heating a cracked straight-through Brazilian disc (CSTBD) gabbro specimen to 200, 400, 500, and 600 °C, followed by 100 thermal cycles. Additionally, acoustic emission (AE) and digital image correlation (DIC) were used to monitor the failure process of gabbro. The results showed that the peak load, fracture toughness, and fracture energy of gabbro decreased with the increased temperature and number of cycles, which was most significant at 500 and 600 °C. Under mode I loading, cracks developed along the loading direction and connected with the prefabricated crack. Additionally, the regions with higher von Mises equivalent strain (Evm) values were concentrated at the loading points and prefabricated crack of the rock sample. The degree of bending of the primary cracks increased, the number of secondary cracks increased, and the Evm values changed significantly as the temperature increased. The phase transformation of plagioclase feldspar at 450 °C and the oxidation of iron- and magnesium-containing pyroxene at 600 °C changed the internal structure of the rock. Cyclic treatment further exacerbated the thermal damage, developing microcracks within the rock and reducing fracture toughness significantly.

High-Temperature Fatigue Testing of Turbine Blades

Abstract This paper evaluates the efficacy of a patented grip for high-temperature fatigue testing by establishing the S-N curve for full-scale nickel-based turbine blades under simulated environmental conditions. Initially, a bending test assessed the stress-displacement characteristics of the component. This was followed by a series of fatigue tests at 950°C, using cyclic bending with force amplitudes from 5.2 kN to 6.6 kN and a constant frequency of 10 Hz. The setup, integrating the grip into a standard testing machine, proved effective for high-temperature tests and successfully determined the service life of full-scale components.

Effect of UV radiation on the high temperature and fatigue performance of SBS modified asphalt and asphalt mixture

In this study, the effects of UV radiation on the high temperature fatigue performance of SBS modified asphalt and asphalt mixtures were analyzed, and the effects of outdoor atmospheric UV radiation were simulated by indoor UV accelerated aging test. The results showed that the increase of UV radiation time led to the increase of creep recovery rate of asphalt and the decrease of irrecoverable creep flexibility, i.e., the resistance to permanent high temperature deformation of SBS modified asphalt was improved. The fatigue cracking resistance of asphalt was weakened and accelerated by radiation. UV radiation increased the rutting resistance of asphalt mixtures and weakened the fatigue resistance at high temperatures. At the same time, UV radiation reduced the aromatic and saturated content of SBS modified asphalt, which led to a reduction in the relative aromatic and saturated content of asphalt mixtures.

Deterioration effect of creep on fatigue properties in QCr0.8 alloy: Damage mechanism and fatigue-creep life evaluation

The QCr0.8 alloy used in the thrust chamber liner wall of the reusable liquid rocket engine is subjected to high-temperature fatigue and high-temperature creep loading. This work investigates the effect of fatigue-creep interaction (FCI) on the fatigue life of QCr0.8 alloy. Experimental results reveal accelerated cyclic softening and decelerated stress relaxation in the alloy under FCI conditions, attributed to creep deformation and stress amplitude growth. The damage evolution mechanism of FCI is revealed by the results of the energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The decrease in fatigue-creep life of the QCr0.8 alloy is attributed to the fracture of the outer surface oxide layer, as well as the coupling development of creep voids and secondary cracks. Finally, a new fatigue-creep life prediction model has been developed, taking into account the increase in plastic strain energy resulting from stress relaxation and creep deformation behaviors. The study results provide substantial theoretical justification for the utilization of QCr0.8 alloy in the thrust chamber wall of reusable liquid rocket engines.

Damage Analysis and Startup Schedule Optimization of Steam Turbine Rotors With an Anisotropic Damage Coupled Viscoplastic Constitutive Model

Abstract The optimization of the operation scheme is of great significance for improving the flexibility of thermal power plants in energy systems dominated by renewable energy. However, thermal stress and corresponding thermomechanical fatigue damage are the main limitations. A unified viscoplastic constitutive model coupled with anisotropic damage is introduced and validated by comparing the experimental and simulated hysteresis loops and cyclic softening curves. The model is implemented into the ansys software by using the USERMAT subroutine to numerically investigate the high-temperature fatigue behavior of a 1000 MW steam turbine rotor on different startup schedules. The critical areas of the rotor are studied in terms of temperature, stress, accumulated inelastic strain, and damage. Based on the damage analysis, the hot start schedule is optimized and validated. The startup time can be significantly shortened within permitted fatigue damage. Moreover, the life expenditure under different loading-up rates is calculated and the extra startup costs can be evaluated accordingly for wider application.

Evaluation of benzaldehyd and dioctyl phthalate modified direct coal liquefaction residue asphalt binder based on rheology and microscopic mechanisms

This study intends to investigate the influence of benzaldehyde and dioctyl phthalate (DOP) on the rheological properties and microstructure of direct coal liquefaction residue (DCLR) modified asphalt binder. The high and low temperature rheological properties and fatigue properties were obtained by dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests. The scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR) tests were conducted to evaluate the mechanism of property improvement in the DCLR modified asphalt binder. The results showed that the addition of DCLR increased the complex shear modulus G*, rutting factor G*/sin δ and fatigue life Nf of base asphalt binder, significantly improving the high temperature deformation resistance and fatigue resistance of base asphalt binder. This was attributed to the hardening effect resulting from the addition of DCLR, which enhanced the elastic properties, weakened the viscous properties and fluidity of asphalt binder. Additionally, the use of benzaldehyde and DOP reduced the creep stiffness S and lower continuous grading temperature Tc of DCLR modified asphalt binder, which compensated for the shortcomings of low temperature rheological properties of asphalt binder. The SEM images indicated that benzaldehyde and DOP significantly increased the compatibility of DCLR with the base asphalt binder. The FTIR tests showed that the addition of benzaldehyde and DOP introduced the aldehyde and ester groups, which were interacted with more polar functional groups in the asphalt to reduce the resistance to movement between the heavy components in the DCLR modified asphalt binder, which promoted the flow of asphalt and the dispersion of DCLR, and as a result, the benzaldehyde and DOP modified DCLR asphalt binder exhibited satisfied rheological properties.

Stress redistribution and stress triaxiality effect on the fatigue life of notched Ni-based single crystal superalloy at 760℃

The multiaxial stress state caused by geometric discontinuities will result in significant differences in the fatigue performance compared to the uniaxial stress state. It is crucial importance to research the notch fatigue behaviors of nickel-based single crystal (Ni-SX) superalloys at high temperature. This study investigated the impact of stress redistribution and stress triaxiality on the fatigue life of notched Ni-based single crystal superalloy at 760℃. The high temperature fatigue tests were carried out on the specimens under different stress ratios and the stress amplitudes under the same life conditions were obtained. A novel anisotropic damage model, incorporating the influence of stress triaxiality is proposed coupled with crystal plasticity theory. Based on experimental findings, an evaluation of the test parameters was conducted.The results showed that Mises stress, maximum principal stress, normal stress of principal stress along the loading direction, maximum principal strain, and strain along the loading direction were inadequate in reflecting the significant variations of samples observed among different stress ratios. However, the stress triaxiality at the unloading valley exhibited a high sensitivity to changes in fatigue life. To evaluate the fatigue life of notched specimens under different stress ratios, an improved Basquin’s type life prediction model was proposed, utilizing the stress triaxiality at the unloading valley. The proposed model demonstrates a favorable normalization trend for the fatigue life of notched specimens subjected to various stress concentration factor (SCF) conditions.

A lightweight image-level segmentation method for steel surface defects based on cross-layer feature fusion

Steel is widely used in the aerospace, machinery and automotive industries. Surface defects not only have a negative impact on the appearance of steel but also significantly reduce its wear resistance, high temperature resistance, corrosion resistance and fatigue strength. Therefore, the detection of steel surface defects is very important to improve the quality of steel production. The limited availability of surface defect samples in the industrial sector poses significant challenges for the accurate detection of defects in high-quality materials. In addition, the existing defect detection model is highly complex and not easy to deploy. To solve this problem, a lightweight defect detection network suitable for steel defects is proposed. The cross-layer feature fusion (CFF) in the design enables effective utilisation of multi-layer semantic features, facilitating the detection of small defects in steel. Secondly, a new loss function is designed to make up for the problems of small data volume and uneven data distribution. The experimental results demonstrate that the steel surface defect detection method proposed in this paper achieves the highest detection performance on widely used public datasets such as RSDDS, NEUS and NRSD-CR(test), while maintaining the lowest model complexity.

Investigating the deformation and microstructural evolution of laser powder-bed fusion of Hastelloy X during high temperature fatigue loading

This study investigates the fatigue behaviour of samples made by laser powder-bed fusion of Hastelloy X (LPBF-HX) with as-built and machined surface conditions at 700 °C under fully reversed strain-controlled cyclic loading. Samples with both surface conditions exhibited initially cyclic hardening followed by cyclic softening under large strain amplitude testing, where a slight continuous hardening was observed for tests with smaller strain amplitudes. The samples with machined surfaces showed longer endurance and higher stress ranges than those with as-built surfaces. Post-fatigue-test EBSD analysis showed the formation of the Goss texture and extensive local strain accumulation in the samples tested under high strain amplitude at 700 °C. Fractography investigations revealed that early crack initiation in the samples with as-built surfaces was from stress concentrations induced by valleys on the rough surface. No evidence of crack initiation induced by pre-existing defects was observed in the machined samples, and the excessive slip activity at the surface was found to be responsible for the crack initiation.

Experimental investigation on high-temperature fatigue failure of different bolts of Ni-based superalloy GH4169 in an aero-engine

Experimental investigation on high-temperature fatigue failure of different bolts of Ni-based superalloy GH4169 in an aero-engine

Microstructure and properties of Ni-based VC and TiVC2 composite coatings fabricated in situ by laser direct deposition

Ni-based VC and TiVC2 composite coatings were prepared on the surface of worn brake discs by laser direct deposition, and the influence mechanism of trace TiC addition on the microstructure and performance of the coating was investigated. The microstructure of the coatings was analyzed by XRD, SEM, EDS, and TEM, which revealed the evolution mechanism of the microstructure during the laser deposition process. The friction wear performance was tested on friction wear equipment. The results showed that VC0.88 was formed by the in-situ reaction of C and V under the action of the laser, which presents dendritic morphology. After the addition of TiC particles, TiVC2 was further synthesized along the TiC particles in addition to dispersed VC0.88 in the coating. It can be seen that the addition of trace TiC particles inhibited the formation of VC0.88 dendrites and enhanced the plastic toughness of the coating. HRTEM calibration proved the existence of TiVC2 and Ni, and there was no obvious orientation relationship between the interface. The friction coefficients of Ni-based VC and Ni-based TiVC2 coatings with Al2O3 balls were 0.59 and 0.51 at room temperature, respectively. After 1.5 h of high-temperature wear at 300 °C and 600 °C, the distribution of wear marks shows a groove and high-temperature fatigue appearance. The TiC-doped coating has better wear properties than the base material and the original coating is expected to meet the requirements for brake discs.

High-temperature Fatigue and Creep Performance of Additively Manufactured NiCu-based Alloy

NiCu-based alloys are frequently employed as a key material for heat exchangers and superheated steam systems where the emphasis is put on the resistance against metal dusting and corrosion in harsh environments and, at the same time, excellent mechanical properties at elevated temperatures. The present contribution delivers the experimental results on high-temperature fatigue and creep performance of additively manufactured NiCu-based Alloy 400 and compares it with conventionally produced material. The fatigue tests were performed in symmetrical force control loading in laboratory air at elevated temperatures. Standard constant stress uniaxial creep tests were carried out up to the rupture at applied stresses ranging from 30 to 150 MPa and temperatures between 600–880°C in a protective argon atmosphere. Results indicate inferior fatigue and creep properties of additively manufactured Alloy 400. This detrimental effect of the manufacturing process on mechanical properties can be caused by several factors, including the orientation of the building direction relative to the loading direction, strong texture in 〈011〉 direction, and also by the presence of defects revealed by means of scanning electron microscopy on fracture surfaces of additively manufactured materials.

Effect of thermal exposure on the microstructure and mechanical properties of Ti60 alloy

The effect of thermal exposure on the microstructure and mechanical properties of Ti60 alloy was investigated in the present study. Meanwhile, the fatigue fracture microscopic appearance characteristics at elevated temperature were analyzed compared, providing the basis to further improve the performance of the series of high temperature titanium alloy. The results show that the yield strength and tensile strength were basically stable under long-term thermal exposure below 600°C, while the elongation decreased with the increase of exposure temperature. Thermal exposure below 800°C did not change the microstructure type of Ti60 alloy, but at higher temperature local β coursing occurred at the grain boundary. When the alloy was exposed above 600°C, Si was obviously concentrated in the grain boundary region, and the maximum concentration was up to 2.5%. With the increase of thermal exposure temperature, the characteristics of high-temperature fatigue fracture of Ti60 alloy change from trans-granular toughness to intergranular brittleness.

Numerical Analysis and Experimental Validation of Temperature Induced Creep and Fatigue life of Inconel 740H and Haynes 282

The Nickel based super-alloys have gained lot of importance in the last decade or so owing to their applications in areas like power generation, military aircrafts, marine propulsion and nuclear reactors. Utilities worldwide are facing increased demand for additional electricity, reduced plant emissions and greater plant efficiency. To meet this challenge, it requires materials with very high temperature creep and fatigue strength and better coal ash corrosion resistance. For the realization of advanced ultra-supercritical (A-USC) thermal plant operating at service temperature and pressure about 700oC to 760oC and 24 MPa respectively, the use of Nickel based super alloys are indispensable. The two A-USC qualified alloys include Inconel 740H and Haynes 282. This study focus on improving the creep and fatigue life of the A-USC qualified alloys by predicting the optimum operating parameters through finite element modeling for temperature induced creep and fatigue analysis of the said A-USC alloys. The influence of various operating parameters like temperature, machining induced residual stress, surface finish, creep duration and fatigue loadings on output parameters like creep strain, elongation, creep and fatigue life were studied. Abaqus/Standard was used for the numerical simulation. Using ANOVA, the most influencing operating parameters were identified. It was observed that the machining induced residual stress and surface finish have greater influence on creep and fatigue life of alloys. Alloy with lower value of machining induced residual stress and better surface finish will have better creep and fatigue life. The proper validation of model was performed by comparing the results with relevant literature.

Enhancement of high-temperature fatigue properties of 310S stainless steel welded joints by strengthened grinding process inducing gradient structure

This study employed the strengthened grinding process (SGP) for surface enhancement treatment of 310S stainless steel weld joints. The surface characteristics and high-temperature fatigue performance were investigated. Initially, the effects of different SGP durations on the surface morphology, microhardness, and residual stress of the weld joints were studied. Subsequently, the high-temperature fatigue life of samples processed through SGP was examined, and the potential mechanisms underlying the impact of SGP on the high-temperature fatigue behaviour of 310S stainless steel weld joints were discussed. The maximum hardness of SGP-6M samples was 337 HV, while the average hardness of UP samples was 163 HV, and the maximum hardness of SGP-6M samples increased by 90.18 % compared to UP samples. The surface residual stress changed from a residual tensile stress of 205.24 MPa to a residual compressive stress of −864.76 MPa. At 25 °C, 500 °C, 600 °C, and 700 °C, the fatigue life increased by 36.9 %, 31.7 %, 25.9 %, and 18.6 %, respectively. This research demonstrates that SGP is an effective method for increasing the high-temperature fatigue life of turbine blades.

Investigation of the high-temperature fatigue mechanism related to altered local short-range order in AL6XN austenitic stainless steel

An increase in crystal local short-range order (SRO), characterized by obvious diffuse intensity maxima at 1/3{422} in the [111]-axis selected area diffraction pattern, is observed in AL6XN austenitic stainless steel subjected to high-temperature low-cycle fatigue deformation. SRO is an ordered fcc structure with nanometer size, which can be well explained by the ordered arrangement of Cr/Mo atomic layers segregated on the {422} crystal plane in austenite. Many planar slip bands are observed in the fatigue sample, the distribution of SROs is highly related with the distribution of dislocations. In situ high-energy X-ray diffraction (HE-XRD) experiments are performed to investigate the deformation behavior of both as-received and fatigued samples under uniaxial loading. The lattice strain evolution reveals an interesting lattice expansion in the initial elastic stage, which provides direct evidence of a decrease in SRO during further uniaxial tensile deformation, indicating that the deformation modes greatly affect the SRO transition. We believe that the high-temperature fatigue damage originates mainly from the accumulation of planar slip bands, accompanied by a local increase in SRO, which promotes work hardening near the final fatigue fracture.

STUDY ON SURFACE INTEGRITY AND ITS INFLUENCE ON HIGH TEMPERATURE FATIGUE BEHAVIOR WHEN TURNING POWDER METALLURGY NI-BASED SUPERALLOY

As a member of the latest generation of powder metallurgy Ni-based superalloy, FGH96 has already been widely applied in the manufacturing of aero-engines because of its distinguished mechanical performances. The surface integrity plays an essential role in the final fatigue life of the machined parts. However, surface modification induced by the machining process is inevitable, which profoundly affects the high temperature fatigue behavior of the manufactured part during the service lifetime. To cover the gap, the present work was carried out to specially study the surface integrity and its influence on high temperature fatigue behavior of powder metallurgy Ni-based superalloy when subjected to the mechanical turning process. The surface integrity, including surface morphology, micro-hardness, and depth-dependent residual stress, was initially characterized under different input parameters. High temperature fatigue tests were then conducted on the processed specimens to correlate the surface integrity and its fatigue behavior. Results showed that input parameters greatly influence the surface condition and thus the high temperature fatigue behavior. Poor integrity on machined surface leads to poor fatigue performance with typical fatigue fracture morphology, including crack initiation, propagation, and final fracture. While fine integrity on machined surface contributes to better fatigue performance. More interestingly, the fracture morphology in this situation shows similarity to the static tensile fracture, which presents shear failure along the direction of maximum shear stress.

Research on low‐cycle fatigue behavior of Ni‐based single crystal superalloy with shaped film cooling holes at high temperature

AbstractFilm cooling holes (FCHs) geometric structure significantly affects low‐cycle fatigue (LCF) of the single crystal turbine blade. This study investigates the LCF behavior of Ni‐based single crystal plate specimens with two different structure FCHs, including elliptical and fan‐shaped FCHs, by high temperature fatigue tests and crystal plasticity simulation. The results show that the LCF life of the fan‐shaped FCHs is shorter than those of the elliptical FCHs. The fracture characteristics and microstructure evolution of different structure FCHs are dissimilar. Oxidation affects the fatigue crack nucleation process at the FCH edge. The resolved shear stress (RSS) around fan‐shaped FCHs is greater than elliptical FCHs under one cyclic stress, and the area with larger RSS is consistent with fatigue crack nucleation position. The early LCF failure is mainly attributed to the high temperature oxidation of the local slip deformation induced by RSS concentration around the FCHs.

Research and Application Progress of High-Entropy Alloys

With the continuous improvement of global technological levels and the increasing demand for high-performance alloy materials in national economic construction, the traditional single principal component alloy is increasingly unable to meet people’s increasing service needs. High-entropy alloys play an important role in aerospace, mechanical manufacturing, biomedicine, energy development and other engineering fields because of their unique physical, chemical and mechanical properties. Based on the concept of high-entropy alloys, the high-entropy effect, lattice distortion effect, sluggish diffusion effect and cocktail effect of high-entropy alloys are represented in this paper. The common preparation methods of high-entropy alloys are summarized according to the classification of melting-casting method, mechanical alloying method and coating method. The strength and toughness, wear resistance, corrosion resistance, high temperature resistance, fatigue resistance, radiation resistance and magnetic properties of the high-entropy alloys are discussed. The application prospect of high-entropy alloys is summarized, and the future research and development direction of high-entropy alloys are prospected on this basis.