Low Temperature Creep Research Articles

A comprehensive study on the rheological properties of desulfurized rubberized asphalt and establishment of micro-scale mechanical models

Recently, understanding the complex relationship between the mechanical properties and material characteristics of desulfurized rubber asphalt has received significant research attention. In this study, the rheological properties of rubber asphalt prepared by three kinds of desulfurized rubber powder are analyzed, and the mechanical response of rubber asphalt mixture is predicted using various mathematical models. Firstly, the rheological properties of desulfurized rubber asphalt are assessed through multiple stress creep recovery test, linear amplitude scanning test, and low-temperature creep test. The results indicate that the high-temperature performance index of desulfurized rubber asphalt is highly sensitive to the degree of desulfurization. As the degree of desulfurization of the rubber powder increases, the fatigue damage rate of asphalt gradually decreases, leading to an increase in the fatigue life. Notably, the difference between the m-critical temperature and stiffness-critical temperature (ΔTc) for only ML40MA does not exceed the threshold value, indicating that it has the best low-temperature cracking resistance. Additionally, the swelling capacity of desulfurized rubber powder in asphalt is better than that of ordinary rubber powder. Finally, the comprehensive performance of desulfurized rubber asphalt is characterized based on the gray correlation method. The gray correlation coefficient of ML60MA is 0.78, which is higher than that of ML40MA and ML80MA, indicating its best overall performance.

Mechanistic Study on the Optimization of Asphalt-Based Material Properties by Physicochemical Interaction and Synergistic Modification of Molecular Structure

In order to investigate the relationship between the molecular structure of fibers and the differences in physicochemical interactions between fibers and asphalt on the performance of fiber-modified asphalt, this paper chose two types of fibers with different chemical structures: straw fiber and polyester fiber. First, the differences in molecular interactions between the two fibers and asphalt were explored using molecular dynamics, then the differences in the adsorption capacity of the two fibers on asphalt components were tested by attenuated total reflection infrared spectroscopy experiments, and finally, the differences in the rheological properties of the two fiber-modified asphalts were tested by dynamic shear rheology and low-temperature creep experiments. The molecular dynamics simulation findings reveal that polyester fibers may intersperse into asphalt molecules and interact with them via structures such as aromatic rings, whereas straw fibers are merely adsorbed on the asphalt’s surface. Straw fibers and asphalt exhibit hydrogen bonding, whereas polyester fibers and asphalt display van der Waals interactions. The results of attenuated total reflectance infrared spectroscopy indicated that polyester fiber absorbed asphalt components better than straw fiber. The rheological tests revealed that the polyester fiber had the highest complex shear modulus in the temperature range of 46–82 °C, and at 64 °C, the phase angle was 4.289° lower than that of the straw fiber-treated bitumen. Polyester fiber-modified asphalt had a 32.48%, 15.72%, and 6.09% lower creep modulus than straw fiber-modified asphalt at three low-temperature conditions: −6 °C, −12 °C, and −18 °C. It is clear that fibers with aromatic rings as a chemical structure outperform lignin-based fibers in terms of improving asphalt characteristics. The research findings can serve as a theoretical foundation for the selection of fibers to produce fiber-modified asphalt.

Characterization of low-temperature creep and stress relaxation of an iron-based shape memory alloy (Fe-SMA) using in-situ synchrotron diffraction

Iron-based shape memory alloys (Fe-SMAs) are e-merging materials with extensive application in civil structures owing to their unique properties, including the shape memory effect. However, it is crucial to understand the time dependent behavior of Fe-SMAs for their effective application as pre-stressing element. In particular, behavior at individual stress, the underlying mechanism, and the transformation kinetics have not been investigated yet. To address these important fundamental research gaps, in-situ compression creep and stress relaxation experiments with high-energy X-ray diffraction (HEXRD) of a Fe-17Mn-5Si-10Cr-4Ni-1(V,C) Fe-SMAs were conducted. The time-dependent behavior of the Fe-SMA was investigated at different stress levels with respect to the yield strength (YS) at room temperature. The experimental result showed that the material exhibits a creep strain of up to 1.84 % and 56 MPa relaxed stress at test stress of 769 MPa (1.6 σYS) within one hour of holding. Stacking fault probability and phase volume fraction quantification provide an understanding of the mechanisms based on different stress levels. The transformation kinetics traced from the characteristics of HEXRD peaks offer further insights on creep depending on the contribution of {hkl} families. The paper concludes with an evaluation of the existing models for predicting creep and stress relaxation of Fe-SMA.

Understanding creep in vitrimers: Insights from molecular dynamics simulations

Vitrimers offer malleability and recyclability due to covalent adaptable networks, however, they are prone to low-temperature creep. In this work, we investigate the molecular mechanisms of vitrimer creep using molecular dynamics simulations. We model the interplay between dynamic bonding with mechanical loading using a topology-based reaction scheme. The creep behavior is compared against cross-linked epoxies with dynamic reactions to understand the unique aspects related to dynamic bonding. It is found that the free volume that arises from tensile loads is reduced in vitrimers through dynamic bond rearrangement. An important feature that distinguishes the secondary creep behavior between epoxies and vitrimers is the orientation of the dynamic bonds during loading. In vitrimers, the dynamic bonds preferentially align orthogonal to the loading axis, decreasing the axial stiffness during secondary creep, resulting in larger creep strain compared to epoxies. Over longer timescales, such increased strain leads to void growth, resulting in tertiary creep.

1/fα noise in the Robin Hood model

Abstract We consider the Robin Hood dynamics, a one-dimensional extremal self-organized critical model that describes the low-temperature creep phenomenon. One of the key quantities is the time evolution of the state variable (force noise). To understand the temporal correlations, we compute the power spectra of the local force fluctuations and apply finite-size scaling to get scaling functions and critical exponents. We find a signature of the 1 / f α noise for the local force with a nontrivial value of the spectral exponent 0 < α < 2 . We also examine temporal fluctuations in the position of the extremal site and a local activity signal. We present results for different local interaction rules of the model.

Laboratory evaluation of performances and thermo-oxidative aging characteristics of high-viscosity modified asphalt

High construction temperatures and complex application conditions make the high-viscosity modified asphalt (HVMA) susceptible to aging. This work presents a comprehensive investigation of the performances and thermo-oxidative aging characteristics of HVMA. Fistly, an instant high-viscosity modifier (HVM) was synthesized and then optimized by entropy weight method. The modification mechanism and high- and low-temperature performances of HVMAs were investigated by the Fourier transform infrared spectroscopy (FTIR), temperature sweep, and low temperature creep tests. Besides, thermo-oxidative aging characteristics were evaluated by the frequency sweep, multiple stress creep recovery (MSCR) and fluorescence microscopy (FM) tests. Results shows that the recommended formulation of instant HVMA (HVMA-I) was 12 % instant HVM and 0.2 % stabilizer. Grafting and cross-linking reactions involved in HVMA-I, thus ensuring the excellent high- and low-temperature performances. The thermo-oxidative aging of HVMA consisted of the modifier degradation and the binder oxidation. Short-term aging produced a marginal effect as a fluctuating change direction for complex modulus. Long-term aging had pronounced effects on the performances of HVMA. At the macroscopic level, the complex modulus was increased and the nonrecoverable creep compliance was decreased; at the microscopic level, the fluorescence area was reduced and phase network was degraded.

Low-temperature creep performance of additive manufactured Ti–6Al–4V

Abstract Additive manufacturing enables the fabrication of versatile and cost-effective metallic-alloy components from a digital data model. This study explores the prospects of selective laser melting (SLM), an additive manufacturing technique, for fabricating Ti6Al4V alloy components from Ti6Al4V alloy powders. Selective laser melting parameters, such as laser power, scanning speed, powder thickness, hatching space, and scanning strategy, are carefully selected through a series of experiments. The metallurgical characteristics (microstructure, grain orientation, and phase composition), microhardness, and creep performance of the as-fabricated specimens are tested and analyzed. The kinetics of phase transformation and rupture mechanism are determined using advanced instrumental characterization tools, such as field emission scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffractometer, and transmission electron microscope.

Evaluation of Cracking Resistance of SMA-13 Hot Recycling Asphalt Mixtures Reinforced by Basalt Fiber.

In the context of green and low-carbon development, energy saving, and emission reduction, hot recycling technology (RT) has been researched, which is divided into hot central plant RT and hot in-place RT. However, due to the aged asphalt binders, the shortcomings of hot recycled asphalt mixtures have become apparent, as in comparison to new asphalt mixtures, their resistance to cracking was inferior and the cracking resistance deteriorated more rapidly. Therefore, it was very necessary to focus on the improvement of crack resistance of hot recycled asphalt mixtures. Basalt fiber has been proved to be able to effectively improve the comprehensive road performance of new asphalt mixtures. Therefore, this paper introduced basalt fiber to hot central plant recycled and hot in-place recycled asphalt mixtures, in order to improve the crack resistance of asphalt as a new type of fiber stabilizer. Firstly, six types of SMA-13 fiber asphalt mixtures were designed and prepared, i.e., hot mixtures with basalt fiber or lignin fiber, hot central plant recycled mixtures with basalt fiber or lignin fiber, and hot in-place recycled mixtures with basalt fiber or lignin fiber. Secondly, the trabecular bending test, low-temperature creep test, semi-circular bending test, and IDEAL-CT were used to comparatively study the changing patterns of low and intermediate temperature cracking resistance of hot recycled mixtures with conventional lignin fibers or basalt fibers. Finally, Pearson's correlation coefficient was used to analyze the correlation of the different cracking resistance indicators. The results show that the low and intermediate temperature cracking resistance of hot central plant recycled mixtures increased by 45.6% (dissipative energy ratio, Wd/Ws) and 74.8% (flexibility index, FI), respectively. And the corresponding cracking resistance of hot in-place recycled mixture increased by 105.4% (Wd/Ws) and 55.7% (FI). The trabecular bending test was more suitable for testing the low-temperature cracking resistance of hot recycled asphalt mixtures, while the IDEAL-CT was more suitable for testing the intermediate-temperature cracking resistance. The results can provide useful references for the utilization of basalt fiber in the hot recycling of SMA-13 asphalt mixtures.

Yield stress anomaly and creep of single crystal Ni-base superalloys – Role of particle size

In the present work we subject the single crystal Ni-base superalloy ERBO1 (CMSX 4 type) to constant strain rate (CSR) and creep testing at temperatures between 1023 and 1223 K. Three material states are considered which have similar particle volume fractions >60% but differ in γ′-particle sizes (material states S, M and L of particle sizes: 240, 390 and 540 nm). In constant strain rate testing, a yield stress anomaly is observed for all three material states, with a yield stress maximum at 1073 K. This increase of strength with increasing temperature is not observed during creep testing at significantly lower deformation rates in this low temperature high stress creep regime, where different elementary deformation mechanisms govern CSR and creep behavior. In contrast, in the low stress high temperature creep regime, stress/strain rate data pairs from CSR creep tests both show decreasing strength with increasing temperature. It is found that in both types of tests the material state M shows the highest strength (highest yield stress and lowest creep rate). This can be rationalized based on a scenario where both, γ-channel and γ′-particle dislocation activities are important. Diffraction contrast transmission electron microscopy is used to study the relevant elementary deformation processes. Details of dislocation arrangements are discussed with a special focus on the role of Kear Wilsdorf (KW) locks, γ′-particle shearing by superlattice stacking faults (extrinsic and intrinsic) and dislocation climb.

Evaluation of hard petroleum asphalt's low-temperature performance and index optimisation based on the grey correlation model

Hard petroleum asphalt (HPA) has good application prospects because of its simple manufacturing process and excellent performance. However, according to previous studies, the performance of HPA at low temperatures cannot be well characterised by commonly used methods. The use of HPA in cold climates is severely constrained. In order to comprehensively evaluate the low-temperature performance of the material, this study used four different types of HPA as the research object, and used the bending beam rheological test ( BBR) to determine the basic rheological properties of the material. On this basis, after fitting and analysing the low-temperature creep compliance curve using the Burgers viscoelastic model, the asphalt was assigned a low-temperature viscoelastic assessment index. The glass transition temperature and sensitivity of HPA were investigated by differential scanning calorimetry (DSC). At the same time, the HPA assessment index at low temperatures was determined systematically by using grey correlation theory.

Assessment of performance characteristics of pavement base course incorporating reclaimed asphalt pavement and asphaltenes

Asphalt pavement is demolished and milled at the end of its service life, resulting in an enormous amount of waste material known as reclaimed asphalt pavement (RAP). Using cold recycling techniques, it is possible to reuse RAP for base course construction. However, using a high amount of RAP could have negative effects on the mechanical properties and durability of the base course. In this study, to improve the performance of asphalt emulsion recycled base course prepared with RAP, asphaltenes derived from Alberta oil-sands bitumen was added to the mixture. The performance properties of the selected mixtures were investigated at high, intermediate, and low temperatures. Testing results and statistical analysis revealed that asphaltenes enhances the high and intermediate temperature performance of the modified mixes significantly. The low-temperature creep compliance of asphaltenes-modified mixtures was slightly lower than the unmodified mixtures, however, the low-temperature properties of the modified mixes were not significantly affected.

Rheological performance evaluation of activated carbon powder modified asphalt based on TOPSIS method

In this study activated carbon powder (ACP) was incorporated into asphalt to substitute a portion of the conventional filler (mineral powder, MP). The dynamic modulus at elevated temperatures, temperature-dependent viscosity sensitivity, low-temperature creep, and the interaction between asphalt and ACP were examined through dynamic shear rheometer testing, viscosity testing, and bending beam rheometer testing. Moreover, statistical methodologies such as the entropy weight method (EWM) and the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) were employed to optimize the proportion of ACP by evaluating the comprehensive rheological behavior of asphalt mastic (including high temperature performance, low temperature performance, flowability, and asphalt-ACP interaction). The findings demonstrate that ACP can enhance the resistance of asphalt mastic to high-temperature deformation to a certain degree. The ratio of creep rate to stiffness (m/S) decreases with the addition of ACP, indicating that ACP may exacerbate the occurrence of low-temperature thermal cracking in asphalt mastic. The interaction ability of asphalt mastic is significantly enhanced when a portion of the filler is replaced with ACP. The loss factor shows significant impact on the comprehensive evaluation. According to TOPSIS analysis, asphalt mastic with a blending proportion of 40% ACP and 60% MP performs better in terms of comprehensive rheological properties.

Low temperature creep of garnet: Insights from blueschist-facies skarn of the Preveli nappe (Crete, Greece)

We present a comprehensive record of deformation, metamorphism, and the state of stress during interaction between garnet-rich skarn and infiltrating fluids in an Eo-Hellenic subduction zone (Preveli nappe, Crete). The structural data and deformation microfabrics of quartz, coupled with petrological constraints, suggest that subduction of the Preveli rocks occurred under epidote-blueschist-facies conditions (T = 360 ± 40 °C, P > 1.0 GPa) and differential stresses >70 MPa. Localized deformation of fine-grained monomineralic grandite of the skarn led to mode I fractures and discrete shear zones along which synkinematic ferri-winchite developed. Brittle-viscous deformation of grandite in high-strain domains was accommodated by cataclasis, incongruent dissolution precipitation creep (IDPC), and incipient dislocation creep (DC). Cataclasis led to strong grain-size reduction and increased permeability resulting in fluid infiltration and enhanced IDPC as is documented by serrated reaction seams along which actinolite and ferri-winchite grew in sequence while replacing grandite. Incipient DC of grandite is indicated by lattice distortion and possible subgrains. Brittle-viscous deformation of grandite occurred at high differential stress (>250 MPa) and was significantly controlled by externally derived fluids, which contributed to hydraulic fracturing and the redistribution and addition of mobile elements.

Fabrication and characterization of multiphase bituminous materials for cold region pavements

In this study, the low temperature creep properties of multiphase bituminous materials (binder, mastic, Fine Aggregate Matrix—FAM, and mixture) were experimentally evaluated, and the impact of size effect on FAM and mixture specimen was also assessed. First, the mix design of mastic and FAM was performed based on the reference mixture Asphalt Concrete (AC) 22 TS. The mathematical adaptation to the boundary sieve method was applied to calculate FAM gradation and binder content. Next, a preparation method was proposed to produce Fine Aggregate Matrix (FAM) in a laboratory environment, and scale-up slab samples were also fabricated for FAM and mixture specimens to evaluate the size effect phenomenon. Finally, three-point bending (3 PB) creep tests were conducted on the multiphase bituminous specimens with different dimensions at -6 °C, -12 °C, and -18 °C with a modified Bending Beam Rheometer (BBR) device and a dynamic loading machine, depending on the sample size. Results indicate that the creep stiffness of the FAM was close to mixtures and much higher than the one observed in binder and mastic. The proposed fabrication approach provides a satisfactory method for preparing a representative FAM phase in the mixture, while the air voids can be easily adjusted during the slab compaction procedure. This study supports the idea of using FAM to discriminate asphalt mixtures for cold regions. The correlation between up-scaled FAM and mixture specimens should be further investigated, including different mixture types and corresponding FAM.

Pivotal role of retained austenite as a low temperature creep controlling mechanism in a martensitic spring steel

The rising demand for electric vehicles urges automotive suppliers to push their limits on the sag resistance of suspension coil springs. However, the mechanism contributing to sag loss in a coil spring or low temperature creep (LTC) in a spring steel is still unclear. Furthermore, the LTC rate-controlling mechanism remains elusive. In the current study, an attempt has been made to unfold the LTC controlling mechanism in a SAE 9254 steel grade. A combined analysis by means of (i) a mechanism-based exhaustion creep model (ECM) and (ii) advanced microstructural characterization prior to and post LTC suggests that dislocation glide, mainly localized in the metastable γ phase, is considered as one LTC contributing mechanism in martempered SAE 9254. Furthermore, stress-assisted martensitic transformation (SAMT) is considered as additional LTC contributing mechanism in SAE 9254 up to the temperature T≤323K. Beyond that temperature strain-induced martensitic transformation (SIMT) takes the place of SAMT. Our approach includes that the LTC rate-controlling mechanisms are stress-assisted recovery (SAR), SAMT, and SIMT especially at elevated temperature T.

New strategy to improve the overall performance of single-crystal superalloys by designing a bimodal γ′ precipitation microstructure

Advanced single-crystal superalloys, developed to improve the high temperature capability of gas turbines, often underperform in low-temperature conditions. This limitation compromises the overall reliability of turbine blades under complex service environments. This study introduces a novel strategy to enhance the overall performance of a fourth-generation single-crystal superalloy. Rapid liquid-nitrogen quenching following the aging treatment promotes extensive nucleation of ultrafine γ′ particles (γ′γ) with an average size of ∼10 nm, precipitated under extremely low supersaturation, as evidenced by high-resolution transmission electron microscopy (HRTEM) and atom probe tomography investigations. The combination of differential scanning calorimetry analysis, density functional theory calculations, and kinetic models verifies the high stability of γ′γ particles at low-temperature conditions around 900 °C. HRTEM observations reveal Orowan bypassing and dislocation cutting of γ′γ particles, leading to additional precipitation hardening by limiting dislocation motion in the γ phase and shear of primary precipitates. Consequently, a bimodal precipitation microstructure comprising γ′γ particles and primary γ′ phase significantly reduces the strain rate of low-temperature creep and nearly doubles the creep rupture life at 800 °C/735 MPa. Simultaneously, high-temperature properties at 900 °C/392 MPa and 1100 °C/137 MPa remain comparable to those of the original microstructure as the primary γ/γ′ microstructure is minimally affected by rapid cooling. This advancement improves overall performance and redefines the importance of small precipitates, broadening microstructure design concepts for future superalloy development.

Evaluating the low-temperature creep properties of polyphosphoric acid-polymer composite-modified asphalt

ABSTRACT The objective of this study was to explore the effect of polyphosphoric acid (PPA) on the low-temperature creep properties of styrene–butadiene-styrene (SBS) and crumb rubber (CR)-modified asphalt binder. PPA-SBS and PPA-CR composite-modified asphalt with different PPA contents were prepared by a high-speed shear method. The low-temperature properties of composite-modified asphalt were studied by bending beam rheometer (BBR) test, and the test results were fitted by the Burgers model to assess the creep property of the asphalt. From the test results, it is demonstrated that the low-temperature properties of polymer-modified asphalt were weakened after PPA was added. At low temperatures, the stiffness modulus (S) of PPA-CR composite-modified asphalt was half that of PPA-SBS, and the creep rate (m) was more than 9.4% higher. The results of relaxation time ( λ ), dissipated energy ratio (DER), and the derivative of creep compliance (J’(t)) showed that the creep property of PPA-CR composite-modified asphalt is better than that of PPA-SBS and SBS-modified asphalt at low temperatures. Moreover, the antiaging ability of polymer-modified asphalt was also ameliorated by incorporating PPA, regardless of SBS or CR.

Performance and Microstructure Characterizations of Halloysite Nanotubes Composite Flame Retardant–Modified Asphalt

To solve the problems of low flame retardant efficiency and weak low-temperature performance of asphalt modified by conventional flame retardants (CFR), in this study, halloysite nanotubes (HNTs) and CFR were used to prepare nanocomposite flame retardants (NCFR) to modify asphalt. A fluorescence microscope (FM), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope/energy dispersive spectrometer (SEM/EDS) were used to characterize the microstructure of NCFR-modified asphalt. An oxygen index meter, Cleveland open cup, and cone calorimeter were used to test the flame retardant properties of the asphalt. A dynamic shear rheometer, bending beam rheometer, and force ductility tester were used to test the rheological properties of asphalt. At the same time, flame retardant–modified asphalt mixtures were prepared to verify the flame retardancy and road performance of the flame retardant–modified asphalt. The research results showed that the asphalt modified with 8% CFR and 1% HNTs (MA/CFR/1% HNTs) showed better dispersibility. The increase of limiting oxygen index and self-ignition temperature and the decrease of heat release rate and smoke production rate of MA/CFR/1% HNTs indicated that it has good flame retardancy. At 64°C, compared with modified asphalt (MA), the rutting factor of MA/CFR/1% HNTs increased by 88.17%, the creep recovery increased, and the irreversible creep decreased, indicating that its high-temperature performance improved significantly. At −18°C, compared with that of MA/CFR, the low-temperature creep stiffness of MA/CFR/1% HNTs decreased by 36 MPa and the creep rate of MA/CFR/1% HNTs increased by 0.034, indicating that only 1% HNTs can improve the effect of degraded CFR on the low-temperature performance of MA. Simultaneously, MA/CFR and MA/CFR/1% HNTs can improve the high-temperature performance and water stability of asphalt mixtures. Adding 1% HNTs to a MA/CFR-modified asphalt mixture can improve the low-temperature performance of the asphalt mixture to the level of the low-temperature performance of the modified asphalt mixture. In summary, the modification of asphalt with 1% HNTs and 8% CFR can effectively improve the flame retardant efficiency and significantly improve the road performance of asphalt.

Thermoregulation, rheological properties and modification mechanism of asphalt modified with PUSSPCMs

Phase change materials (PCMs) can regulate asphalt temperature through thermal storage properties to prevent thermal damage in asphalt pavements. However, the effects of PCMs on the thermoregulation and rheological properties of asphalt require further study. In this study, polyurethane solid–solid phase change materials (PUSSPCMs) were prepared to impart thermoregulation properties to asphalt, and the effects of PUSSPCMs on the rheological properties and microscopic characterization of asphalt were investigated. The PUSSPCMs were produced by different soft segment mass fractions (70 %, 80 %, and 90 %), and they were used to prepare modified asphalt with varying contents (3 %, 5 %, and 7 %). Thermoregulation testing system, dynamic shear rheology (DSR), bending beam rheology (BBR) tests, differential scanning calorimetry (DSC), infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were conducted to determine the thermoregulation, rheological properties, and modification mechanism of PUSSPCM-modified asphalt, respectively. The results show that the thermoregulation property of PUSSPCM-modified asphalt improves with the increase of soft segment mass fraction and content, 7 % P90 asphalt exhibits the best thermoregulation property with the excellent delayed time (1105 s) and temperature difference (7.1 ℃). The high-temperature rutting resistance of the modified asphalt is enhanced by decreasing the soft segment mass fraction and increasing the content of PUSSPCMs, with the 7 % P70 being the best asphalt type. The 7 % P90 asphalt exhibits the optimum low-temperature creep performance due to a higher soft segment mass fraction. The modified asphalt may be a physical modification since no new characteristic peaks appear. With the increase of soft segment mass fraction, the PUSSPCMs in asphalt transform from elastomer to a ribbon-like structure. Furthermore, the microscopic roughness (Sq) and Young's modulus of the modified asphalt decline with the increase in soft segment mass fraction and content of PUSSPCMs, implying an increase in microscopic crack resistance and a decrease in elasticity.

Creep strengthening mechanisms of a superlattice γ′-strengthened Co–Al–W–Ta–Ti single crystal superalloy at steady-state conditions under compressive stresses

The strengthening mechanism of steady-state creep is a critical factor in developing advanced superalloys. In this study, the steady-state creep mechanisms of a superlattice γ′-strengthened Co–Al–W–Ta–Ti single crystal superalloy are investigated with the creep conditions of 750 °C/800 MPa, 900 °C/420 MPa and 1000 °C/137 MPa. Results suggest that the microstructures of steady-state creep samples are significantly different under the above three experimental conditions. A detailed TEM study shows that, Lomer-Cottrell locks and stacking faults interactions are responsible for the low creep rate at low temperature and high stress creep regime, dislocations cross-slip and the dislocation tangles contribute the main creep resistance at intermediate temperatures and moderate stress creep regime, interactions of stacking faults and dislocation networks are the strengthening mechanism for the high temperature and low stress creep regime. The steady-state creep rate of investigated alloy follows the classical power law equation, and the creep activation energy calculated by the power law equation is 378.46 kJ/mol. The results of this study provide insights into the effects of temperature and stress on steady-state creep mechanisms, and high activation energy makes the γ′-strengthened Co–Al–W–Ta–Ti single crystal superalloy an attractive candidate for further study as a high temperature structural material.