High Temperature Creep Behavior Research Articles

Research Progress on the Relationship Between Microstructure and Properties of AISI 321 Stainless Steel

AISI 321 stainless steel is widely used in chemical pipelines and nuclear power, prompting research on its high-temperature performance and corrosion resistance. This review focuses on the effects of alloy elements, second-phase particle formation, and heat treatment processes on the microstructure and properties of AISI 321 stainless steel. Fine tuning of alloying elements can affect the mode and effect of dynamic recrystallization, altering the high-temperature flow deformation of AISI 321 stainless steel. In order to achieve phase equilibrium, the relationship between corrosion resistance and high-temperature creep behavior and high-temperature mechanical behavior in the presence of second-phase particles was also analyzed. This review outlines the basic heat treatment procedures for improving material properties, providing a new perspective for solution treatment and improving corrosion resistance. In addition, the latest research progress on other factors affecting the high-temperature performance of AISI 321, such as coatings, was briefly introduced.

Effects of Ta on the high temperature creep behavior and deformation mechanism of a Ni-based single crystal superalloy

The effects of Ta on the high temperature creep behavior and deformation mechanism in a Ni-based single crystal (SX) superalloy were investigated at 1120 °C/137 MPa. Ta was regarded as an essential strengthening element of the γʹ phase in the alloy, and the results indicated that the increase of Ta prolonged the creep rupture life. In this work, the addition of Ta increased the volume fraction of the γʹ phase and narrowed the γ channels, making the dislocation bowing out at the primary stage of creep more difficult. As creep continued, with a lower effective diffusion coefficient of alloying elements and larger γʹ raft thickness, the alloy with 6.5 wt% Ta addition was considered to possess the lower dislocation climbing rate, which reduced the minimum creep rate of the alloys. Subsequently, it was noted that the density of superdislocations in γʹ phase was clearly reduced with the increase of Ta. This was supposed to be the elevated Ta content in the alloy, which increased the lattice misfit and led to the formation of a denser dislocation network, thereby enhancing the interfacial strengthening effect and effectively preventing the cutting of superdislocations. The Ta effect on high-temperature creep was systematically summarized in this study, which was an important guideline for further composition design and optimization of Ni-based SX superalloys.

Stress sensitivity and its influence on high-temperature creep behavior of a novel 2nd-generation low-cost nickel based single crystal superalloy

To meet the application requirements under complex service conditions for aero engine blades, the influence of stress-state on creep behavior of a self-designed Re-low Ni-based single crystal superalloy at 1038 °C over a wide stress range of 137–207 MPa was investigated. With applied stress decreasing from 172 to 137 MPa, the creep life rapidly extends by a factor of 2.41, showing strong stress dependence. Further, the creep mechanisms under different stresses are discussed based on microstructural characterization and threshold stress calculation results. With the increasing applied stress, interfacial dislocation networks exhibit sparse and irregular shapes. Particularly, in necking zone of the fractured specimen at 1038 °C/137 MPa, due to the long-duration accumulation of deformation storage energy, dislocation arrays within γ′ rafts gradually evolve into dislocation walls through recombination and annihilation of dislocations, then develop into subgrain boundaries. Finally, some recrystallization grains with large misorientations (>10°) form by subgrain-rotation. Moreover, based on the calculated threshold stress, dislocations climbing can play a major role in creep deformation throughout the steady-state stage under a stress range of 137–207 MPa. Nevertheless, with the arrival of tertiary stage, the increasing actual stress resulted from necking deformation can also promote dislocations to cut or bypass γ′ rafts under lower stresses (137 and 172 MPa), which is consistent with the final evolution of dislocation substructures. Overall, the findings from this work are helpful to understand the high-temperature creep mechanism of low-cost single crystal superalloys, so as to improve the creep resistance of materials.

The high temperature creep and fracture behavior of Inconel 718 produced by additive manufacturing

High-temperature creep tests of additively manufactured (AM) and wrought nickel alloy 718 (IN718) were conducted at 650 °C and 704 °C at stresses ranging from 316 to 819 MPa. The AM alloy had a greater creep strength than the wrought alloy at nearly all testing conditions due to increased volume fractions of γ” in the matrix and carbides at grain boundaries; however, the creep rupture ductility of the AM material was significantly reduced at all testing conditions. Secondary ion mass spectrometry (SIMS) revealed that sulfur segregation, resulting from a lack of Mg in the AM alloy, is the most plausible explanation for the observed ductility loss in AM IN718. Overall, this work focuses on understanding and defining the mechanism of embrittlement in AM IN718.

Role of threshold stress in creep of IN740H, a γ′-lean Ni-based superalloy

IN740H, a Ni-based superalloy comprising a low-volume fraction of γ′, is a candidate material to be used over long periods at high temperatures and stresses, as conditions prevalent in advanced ultra-supercritical (AUSC) power plants. In this study, IN740H has been tested at temperatures above 700 °C to gain mechanistic insights into its high-temperature creep behavior. The material showed classic signatures of the presence of threshold stress, marked by observation of a high apparent creep stress exponent, n, (e.g., 10 at 750 °C) and a high apparent activation energy for creep, Qc (e.g., ∼545 kJ/mol), along with a rapid increase in n at lower stresses. Accounting for the threshold stress led to a decrease in the values of n and Qc to 4 and 280 kJ/mol, respectively. Furthermore, the transmission electron microscopy and atomic scale compositional analysis reveal the pinning of dislocations at γ-γ′ interface and segregation of Co, Cr and Mo atoms in the regions of γ-γ′ interface rich in dislocations. The above combination of n and Qc and the observation of dislocation pinning at the γ-γ′ interface indicate the dislocation climb over γ′ as the dominant creep mechanism in this γ′-lean Ni-based superalloy, with the detachment of dislocations from the γ-γ′ interface, augmented by the segregation of Co, Cr and Mo, as the mechanism responsible for the realization of the threshold stress. This work, thus, provides a new impetus to research on the long-term structural integrity of γ′-lean Ni-based superalloys exposed to extreme service conditions.

High-temperature creep and corrosion behavior of 316LN stainless steel in oxygen-saturated sodium

The high-temperature performance and sodium corrosion of in-core components are the main problems of liquid sodium-cooled reactors, and low-carbon nitrogen-controlled 316 stainless steel (316LN) is the main research and development direction of the main materials for the core of sodium-cooled fast reactors. In this work, the creep behavior of 316LN in oxygen-saturated liquid sodium at high temperatures (650 ℃, 700 ℃ and 750 ℃) was tested and compared with the results of creep tests in air at the same conditions. It is found that the creep life in the sodium environment is reduced by 63.44%, 67.93% and 40.07%, respectively. The specimens in oxygen-saturated sodium exhibit reduction in ductility, selective dissolution as well as oxidative corrosion. The corrosion mechanism of 316LN under external loading in oxygen-saturated sodium is illustrated.

Elevated-temperature creep properties and deformation mechanisms of a non-equiatomic FeMnCoCrAl high-entropy alloy

This study investigates the high-temperature creep behavior of a novel (Fe50Mn30Co10Cr10)91Al9 non-equiatomic high-entropy alloy (HEA) spanning the temperature range of 873–973 K and stress conditions from 50 to 90 MPa. Microstructural examinations and theoretical analyses are conducted to elucidate the performance parameter and deformation mechanisms of the HEA under sustained high-temperature conditions, providing an theoretical basis for application prospects. The results indicated that the cold-rolled and annealed alloy exhibited excellent creep resistance under conditions of 923 K/50 MPa and 873 K/50 MPa. The creep mechanism of the HEA at 923 K was identified as being primarily controlled by dislocation climb, as determined by stress exponent fitting calculations. Differing from common equiatomic HEAs, creep in these cases is controlled by solute atoms and mobile dislocations mechanisms. Microstructural characterization validated identified creep trends and deformation mechanisms, revealing diverse micro-mechanisms, such as dislocation jogs and new phase precipitation under various deformation conditions. Additionally, the 'climb-dominant mechanism model' was used to discuss the self-consistency of experimental parameters, providing in-depth insights into the contribution of elemental parameter variations to dislocation climb, as well as the reasoning behind creep performance concerning stress and temperature dependencies.

Interplay between high-temperature creep deformation behavior and nanoscale precipitate evolution in a newly designed Fe–Ni-based superalloy

In an endeavor to achieve the critical goals of carbon neutrality, an explorative study was conducted to scrutinize the precipitate evolution and high-temperature creep behavior of an innovative and cost-effective Fe–Ni-based superalloy that was meticulously engineered for the next-generation ultra-supercritical (USC) power plants. The creep experiments conducted at temperatures and stresses of 650 °C/280 MPa (17,179 h), 675 °C/250 MPa (10,271 h), and 700 °C/250 MPa (2378 h), coupled with proficient data fitting were employed to accurately assess the long-term service performance of the superalloy under real-world operational environments. Though it can withstand theoretically an intense stress of 130 MPa at 700 °C for approximately 30 years as calculated by the Larson-Miller equation, its performance was not without a degree of perceived vulnerability. This was primarily traced to the conspicuous coarsening behavior of the precipitate-free zones (PFZs)/discontinuous coarsening zones (DCZs) formed in the grain boundaries (GBs) on a longer time scale. It had a significant diminishing impact on the overall strength of the GBs, resulting in a recorded creep life that was considerably shorter than initially projected. Moreover, a synergistic mechanism between PFZs/DCZs with TiC carbides was advanced to interpret the intergranular fracturing dynamic, which was postulated due to the evidence gathered from electron backscatter diffraction (EBSD), highlighting that the banded distribution of TiC carbides circumambient to GBs engendered considerable stress aggregation. Conversely, the plentiful supply of coincidence site lattice (CSL) boundaries disrupted the continuous network structure of random high-angle grain boundaries (HAGBs), thereby creating an effective barricade against the proliferation of cracks. These empirical findings paved the way for the proposition of an enhanced blueprint and the industrial utilization of such.

High-temperature creep behaviour and deformation mechanism of a high-concentration Re/Ru single-crystal nickel-based alloy

In this study, the deformation and damage mechanisms of a high-concentration Re/Ru single-crystal nickel-based alloy at ultrahigh temperatures are studied via creep performance tests, microstructural observations and dislocation configuration diffraction contrast analyses at 1170 °C. The results show that the alloy has good mechanical properties. In addition, the creep life is 155 h at 1170 °C and 120 MPa. During creep, dislocations moving in the γ matrix can react with each other to form a dense and complete dislocation network. This dense and complete dislocation network can effectively prevent dislocations from shearing into the γ′ phase and reduce the creep rate during the steady-state creep period. In the late stage of ultrahigh-temperature creep, stacking faults are found in the γ′ phase, indicating that the alloy has a low stacking fault energy and that the stacking faults that form in this alloy can serve as obstacles for dislocation movement. In addition, the dislocations that cut into the γ′ phase in the late stage of ultrahigh temperature creep can cross-slip from the {111} plane to the {100} plane, forming a KW lock, which can inhibit the slip and cross-slip dislocation movement modes. Therefore, the presence of dislocation networks, stacking faults and KW locks in alloys is the main reason for the relatively low strain rate and good creep resistance of these alloys under ultrahigh-temperature creep conditions. In the late stage of creep, the initiated dislocations slip in two orientations, resulting in kinking of the rafted γ′ phase and crack initiation at the top interface of the twisted rafted γ/γ′ two phases. Under the action of shear stress, the crack generates tensile stress perpendicular to the stress axis, and it expands in this direction. This crack is the damage mechanism of the alloy during ultrahigh-temperature creep.

Initial Vacancy-Dependent High-Temperature Creep Behavior of Nanocrystalline Ni by Molecular Dynamics Simulation

Nanocrystalline metals possessing excellent mechanical strength have great potential to replace traditional metal materials as structural materials, but their poor resistance to creep deformation seriously restricts their engineering applications at high temperatures. The high-temperature creep behavior of nanocrystalline Ni with different volume fractions of initial vacancies ranging from 0% to 10% was studied systematically by molecular dynamics simulation in this study. The results showed that the steady-state creep displacement first increased and then decreased with increasing initial vacancy concentration, reaching the maximum when the initial vacancy concentration was 6%. The microstructural characteristics, such as quantity increment and distribution of the vacancies, the number and types of dislocations, and shear strain distribution during creeping, were analyzed in detail. The deformation-induced vacancies formed at the grain boundary (GB) in the initial creep stage, and their variation trend with the initial vacancy concentration was consistent with that of the creep displacement, indicating that the initial vacancy-dependent high-temperature creep behavior of nanocrystalline Ni was mainly determined by the rapidly increasing number of vacancies at the GB in the initial creep stage. Afterwards, the deformation-induced, vacancy-assisted 1/6{112} Shockley partial dislocation activities dominated the creep deformation of nanocrystalline Ni in the steady-state creep stage. The results can provide theoretical support for expanding the application of nanocrystalline metals from the perspective of crystal defect engineering.

Experimental Study on High-Temperature Creep Behavior of Full-Locked and Galfan-Coated Steel Cables

Experimental Study on High-Temperature Creep Behavior of Full-Locked and Galfan-Coated Steel Cables

Tensile creep mechanisms of Al-Mn-Sc alloy fabricated by additive manufacturing

The incorporation of Sc/Zr elements into aluminum (Al) alloys provides great opportunities for high temperature applications, due to the high coherency with the Al matrix, the high thermal stability and the high strengthening potentials of the generated Al3(Sc,Zr) precipitates. In this study, the microstructure, thermal stability, high temperature tensile and creep behaviors of additively manufactured Al-Mn-Sc alloy were systematically evaluated. The Al-Mn-Sc alloy demonstrated sound high temperature yield strength as compared with other reported Al alloys made by additive manufacturing. However, the formed large area fraction (approximately 60%) of fine grain boundaries significantly promoted the dislocation annihilation and reduced the creep threshold stress, though the inherent thermally stable solutes and/or precipitates contributed to its high creep activation energy. On the other hand, the primary Alx(Mn,Fe) and Aly(Sc,Zr) particles and the fine grain boundaries severed as the potential cavity nucleation sites, enhancing the cavity kinetics during creep loading. The cavity nucleation and coalescence process, which basically dominated the tertiary stage of the creep lifetime and led to the final fracture, were further revealed through a cavity evolution model. Future creep-resistant Al alloy design outlook, especially for the inoculates modified Al alloys with fine grain structures, were proposed based on the present findings.

Significant enhancement in high temperature performance of TiAl matrix composites by a novel configuration design

Ti5Si3/TiAl composites were successfully prepared by pressure infiltration and subsequent reactive annealing. Final microstructure of Ti5Si3/TiAl composites was dependent on the reactive annealing temperature, which varied from 1350 °C to 1420 °C, two typical microstructures could be achieved: (i) An unique core-shell structure (Core: fully lamellar α2-Ti3Al/γ-TiAl with in-situ synthesized Ti5Si3 particles predominantly distributed at the interfaces of α2/γ lamellar colonies; Shell: equiaxed γ-TiAl with Ti5Si3 particles distributed in γ grain boundaries); And (ii) A novel quasi-network structure composed of fully lamellar α2/γ and a majority of Ti5Si3 particles with a quasi-network distribution. The formation of the two microstructures could be attributed to the chemical composition heterogeneity which was caused by the difference in interdiffusion rate of Ti and Al elements in different annealing temperatures. The comparative investigations on high temperature tensile properties and creep behavior showed that the core-shell Ti5Si3/TiAl composites exhibited a better specific strength (165 MPa⋅g−1⋅cm3) and higher ultimate tensile strength (633 MPa) at 800 °C, which was 12 % higher than that of the quasi-network Ti5Si3/TiAl composites. While the creep behavior analysis showed that in compassion with equiaxed γ phase, the slip distance of dislocations in fully lamellar α2/γ phase was shorter, impeding the motion of dislocations more effectively. And core-shell Ti5Si3/TiAl composites possessed a large number of grain boundaries concentrating in the shell which became weaker in the high temperature, facilitating the formation of creep pores in the shell and the final premature fracture. Hence, the quasi-network Ti5Si3/TiAl composites containing a higher content of fully lamellar α2/γ exhibited a better creep resistance than that of core-shell Ti5Si3/TiAl composites. More importantly, the steady state creep rate at 750 °C under the fixed stress of 250 MPa of quasi-network Ti5Si3/TiAl composites was relatively low, only 3.305 × 10−8 s−1, comparable to that of third-generation TiAl alloys.

Study on creep characteristics and the isochronous stress–strain curve of Ni-Cr-Mo superalloy

ABSTRACT C276 superalloy is considered as a potential structural material for advanced nuclear reactor with good mechanical properties and corrosion resistance. High-temperature creep behaviour of C276 alloy was investigated in the temperature range of 650°C–700°C and at stresses of 140–430 MPa. A linear relationship was fitted between stress and minimum creep rate in the logarithmic coordinate system. The rupture time is analysed for life prediction in terms of isotherm extrapolation method, Monkman–Grant relation, and Larson–Miller parameter method, respectively. The isochronous stress–strain curves as a means of representing stress–strain–time relations under creep conditions were established by the parameter method. The fracture surface morphology of ruptured specimens was characterised by a scanning electron microscope to elucidate the failure mechanism.

Creep behavior of sintered nano-silver at high temperature: Experimental and theoretical analysis

Creep experiments were conducted on self-designed cylindrical specimens of sintered nano-silver at temperatures ranging from 298 K to 523 K. The creep behavior of sintered nano-silver at different temperatures was investigated. It was observed that an increase in temperature led to significant softening, accompanied by an increase in the maximum strain from 0.26 to 0.889. Additionally, the creep rate showed accelerated decay, with the rate rapidly approaching zero for temperatures exceeding 373 K, indicating a strong temperature dependence. Based on material microstructure characterization techniques and finite element analysis, it shows that the high temperature sensitivity of sintered nano-silver creep is primarily attributed to void formation. A new theoretical model has been developed based on the theory of entropy increment, which can accurately predict the creep strain of sintered nano-silver compared with the experimental data, the key factors influencing the creep behavior has been analyzed. The current study presents a more accurate description strategy regarding the high-temperature creep behavior of sintered nano-silver. Compared with the conventional creep models, the proposed model can accurately capture the softening properties of sintered nano-silver.

Effect of substituting Gd with 3 wt% Nd on high temperature creep behaviors of peak-aged Mg-10Gd-0.4Zr casting Mg alloy

In this paper, the high temperature creep behaviors of peak-aged Mg-10Gd-0.4Zr and Mg-7Gd-3Nd-0.4Zr casting alloys were investigated. The results showed that substituting Gd with 3 wt% Nd promoted precipitation of the β′ phase with higher number densities and larger aspect ratios, which led to the higher tensile mechanical properties of the peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy at both room and elevated temperatures. The peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy had better tensile creep properties at temperatures of 200 °C–225 °C. However, the peak-aged Mg-10Gd-0.4Zr casting alloy showed better creep resistance when the creep temperature ≥250 °C. The creep mechanism for the peak-aged Mg-10Gd-0.4Zr casting alloy was dislocation climb assisted by grain boundary diffusion under all experimental conditions, while the creep mechanism of the peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy transformed from dislocation glide at 200 °C–225 °C into dislocation cross-slip above 250 °C. Due to the faster transformation from β′ phase into β1 phase in peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy, the blocking effect of precipitation on dislocation movement was weakened. And a larger number of basal < a > dislocations accumulated in the grain boundary region, leading to precipitate free zones (PFZs) widening more obviously in the peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy, and which well explained the reason why the creep resistance of peak-aged Mg-7Gd-3Nd-0.4Zr casting alloy deteriorated rapidly above 250 °C.

Effects of aging and nitridation on microstructure and mechanical properties of austenitic stainless steel

Understanding the effects of in-service microstructural changes in metal alloys on the mechanical performance and remaining life of equipment is a critical part of integrity management in industrial plants. However, the effects of processes such as carburization or nitridation are not accounted for in industry-standard life assessment methodologies such as those provided in the API 579-1/ASME FFS-1: Fitness-For-Service standard. This is problematic for the austenitic stainless steel Alloy 800H, which typically operates in the creep regime and has been reported to suffer nitriding during high-temperature service in air. Despite this being one of the most common service environments for 800H, the impact of nitriding on in-service performance and implications for remaining life assessment have not been well-studied for this alloy. In this work, we characterize the microstructures of as-received, aged, and nitrided Alloy 800H tube material, and correlate observations with room-temperature tensile properties and high-temperature creep behavior. We show that while the creep properties of aged 800H material can be captured by the widely-used MPC Project Omega creep model and API 579-1 Omega properties for 800H, nitrided material properties fall outside of the expected bounds, and therefore remaining life cannot be reliably predicted using this method without experimental data.

High-temperature compressive creep behavior and mechanism of Hf6Ta2O17 ceramic as a candidate for thermal barrier coatings

A novel Hf6Ta2O17 ceramics is prepared by a solid-state reaction method. High-temperature creep behavior of Hf6Ta2O17 and 8YSZ ceramics are investigated by compressive creep test combined with a digital image correlation (DIC) method. It is found that the creep mechanism of Hf6Ta2O17 ceramics is controlled by grain boundary sliding associated with dislocation movement (stress exponent ∼2-3, and activation energy of 600–620 kJ/mol). Grain boundary sliding accommodated to the interface reaction is the main creep mechanism of 8YSZ ceramics (stress exponent ∼2, and activation energy of 425∼465 kJ/mol). Hf6Ta2O17 ceramics have higher creep resistance than 8YSZ ceramics under the same conditions.

High temperature creep study on thermally grown oxide by tensile combined with a digital image correlation method

A thermally grown oxide (TGO) layer usually generates at the interface between the ceramic coating and the bond coating during the long-term high temperature service. TGO creep can affect the service life of thermal barrier coatings. In this paper, a dense TGO layer with a thickness of 4 μm is formed on the surface of the PtAl bond coating. The high-temperature creep behavior of the TGO layer is investigated by tensile combined with a digital image correlation method. The creep mechanism of TGO at 750 °C–950 °C is dislocation creep (stress exponent ∼4, and creep activation energy of 706–815 kJ/mol). The creep strain rate of TGO at 750 °C–950 °C is in the range of 4.7 × 10−6 s−1–4.7 × 10−4 s−1. The failure behavior of the TGO layer is significantly affected by temperature and applied stress. As the temperature and stress increase, the surface vertical cracks initiate at the TGO surface and propagate to the interface of TGO/PtAl bond coating, leading to the delamination and cracking of TGO layer.

High-temperature creep behaviors of polybutene-1 with different chain microstructure and molecular weight

The creep resistance of polymer determines the dimensional stability of product under stress. The isotactic polybutene-1 (iPB) with outstanding high-temperature creep resistance and stress-crack resistance is applied widely in the field of hot-water pipes. Although the chain information including weight-average molecular weight (Mw) and aggregate structures of isotactic polybutene-1 (iPB) influence the creep resistance, the crucial factor affecting the creep behavior greatly is unclear. In this work, a series PB samples with varied Mw, isotacticity and configurational sequence were synthesized and characterized based on Gel Permeation Chromatography (GPC), solvent fractionation and Nuclear Magnetic Resonance Spectroscopy (NMR). The Differential Scanning Calorimetry (DSC), Wide-angle X-ray diffraction (WAXD) and Small angle X-ray scattering (SAXS) were used to characterize the aggregation structures of PB samples. The stress-strain behaviors and 95 °C creep deformation of these PB samples were testes by tensile test and Dynamic Mechanical Analysis (DMA), respectively. It was found that these PB samples showed different chain microstructures like 88–99 wt% high isotactic PB (HiPB) fractions, 90–97.6 mol% tetra-meso placements (mmmm) in HiPB fraction, and 50 × 104-160 × 104Mw. Increasing the molecular weight, isotacticity or configurational sequence mmmm enhanced the creep resistance of PB, while mmmm configurational sequence played more important role in creep resistance of PB through adjusting the aggregation structure (crystalline domains) of the final product greatly. Exploring the influencing factors of creep resistance provided guidance for the synthesis of high-performance PB for high-temperature pipe application.