Search

This study investigates the microstructural evolution and its effect on the fatigue performance of a novel nickel-based powder superalloy FGH4113A (WZ-A3) after long-term aging at 760 °C and 815 °C. The results show that long-term aging both at 760 °C and 815 °C has no significant effect on the grain size and morphology of the alloy. After aging at 760 °C for up to 2020 h, the size of the γ′ phase remains unchanged, and its morphology transitions from nearly square to nearly spherical. During long-term aging at 815 °C for 440 h, γ′ phase coarsening and spheroidizing occur simultaneously. With prolonged aging time, the size and spheroidization degree of the γ′ phase further increase. During long-term aging up to 440 h at 760 °C, the dispersed granular MC and M6C carbides dissolve and re-precipitate. By 2020 h of aging, flocculent carbides precipitate and non-continuous M6C and M23C6 accumulate at grain boundaries. After long-term aging at 815 °C for 440 h, flocculent carbides begin to precipitate within the grains. By 2020 h of aging, a large amount of flocculent carbides precipitate with significant coarsening and enrichment of the grain boundary carbides. Due to the insignificant coarsening of the γ′ phase as well as the enrichment and precipitation of the grain boundary carbides, the fatigue performance of the alloy decreases slightly after long-term aging. [ABSTRACT FROM AUTHOR]

One of the main issues that asphalt encounters over its service life is aging, which causes the material to change from a flexible to a solid condition and increases its susceptibility to breaking and fissures. Asphalt ages due to the oxidation of the asphalt and the evaporation of volatile components. This paper's primary objective is to investigate the impact of aging on the site-modified asphalt mixture. Asphalt pavements usually age due to the binder's lighter and the asphalt's oxidizing evaporating. After being prepared, asphalt concrete mixtures were aged over an extended period. For Marshall compacted specimens, the process entails long-term aging periods for the asphalt within a year of its service. At its ideal asphalt concentration, the effects of varying aging durations on the Marshall Properties, The combination becomes stiffer as it ages longer, which raises Marshall Stability and the robust modulus, which raises the mixtures' resistance to irreversible deformation. Compared to the control mixture, the one-year long-term aging increases the Marshall stability and resilient modulus by 35.33% and 28.59%, respectively. [ABSTRACT FROM AUTHOR]

A drawback of recycled mixtures containing reclaimed asphalt is their increased stiffness, further worsened by the accelerated aging of binders in extreme weather conditions. Previous studies have shown that while rejuvenating agents can mitigate some of these issues by improving flexibility and reducing brittleness, they often present challenges, such as performance variability and the potential for rutting. This study aims to develop an optimal blend of reclaimed bitumen, a rejuvenating agent, and pure bitumen to achieve rheological properties similar to a control 35/50 pen-grade bitumen for road paving. Hence, the rejuvenated binders comprised 30:70 blends of reclaimed asphalt bitumen and 50/70 pen-grade bitumen, adding 0.2% to 0.6% of a rejuvenating agent by mass of the reclaimed asphalt. Sample testing included conventional penetration grade, softening point, and viscosity tests, followed by dynamic shear rheometer tests under unaged, short-term, and long-term aging conditions. The results show that the binder blend with 0.4% rejuvenator closely resembles the rheological properties of 35/50 pen-grade bitumen. This blend exhibits a 20% to 55% stiffness reduction for recycled mixtures with 30% reclaimed asphalt. Notably, the rejuvenated binders exhibited a similar level of aging resistance to the control bitumen, with a marginal difference of less than 5% in aging ratios. Meanwhile, large strain amplitude tests showed the importance of defining maximum rejuvenating incorporation rates in recycled mixtures to avoid rutting problems, where binders with 0.4% rejuvenator doubled the rutting potential (Jnr values). This innovative study highlights the potential for enhancing recycled mixtures' performance by evaluating rejuvenated reclaimed binders' rheology subjected to different aging conditions, thus contributing to sustainability in pavement construction. [ABSTRACT FROM AUTHOR]

In K444 alloy, the evolution of carbides during stress aging (creep) and stress-free aging at 900 °C for 5000 h, and interrupted at 3000 h were investigated, combining microstructure characterization and quantitative statistics method. After stress-free aging for 5000 h, the volume fraction of intragranular MC and M6C carbides decrease from 0.48 % to 0.66 %–0.26 % and 0.48 %, respectively, while that of M23C6 carbides increase to 0.28 %. The two degradation behaviors can be concluded as MC + γ → M6C + M23C6 + γ′ and M6C + γ → M23C6 + γ′ respectively. The former controlled by the diffusion of Ti occurred earlier, while the latter determined by the diffusion of W and Mo mainly happened later. The applied stress did not change degradation reactions while accelerate the degradation rate slightly. During stress-free aging, the morphology of grain boundaries (GBs) changed from discrete distribution to semi-continuous and then to continuous chain, and the content of MC and M6C carbides decreases while that of M23C6 carbides increases. The applied stress markedly promotes above behaviors. Especially, the completed continuous chain formed before 3000 h. Moreover, the applied stress induced the formation of cavitation on the GBs, which is attributed to the following reasons. First, it can accelerate the degradation of GBs and decline the GBs strength. What's more, dislocations pile up on the GBs and cause a high level of stress concentration. Finally, the new generated phase interfaces have a greater deviation with its adjacent carbides, weakening the binding force of GBs.

The effects of alloying elements on the microstructure evolution and properties of GH2107 superalloy during long-term aging are investigated by optical microscope, scanning electron microscope, and transmission electron microscope. The results indicate that the microstructure of the alloy becomes unstable with the prolongation of aging time. Cr element promotes the precipitation of M23C6 carbides at grain boundaries, and Fe element inhibits the precipitation and growth of M23C6 carbides at high temperature. At the same time, high Fe promotes the growth of γ' phase and the precipitation of TCP phase, which has a certain influence on the plasticity and strength of the alloy. The yield strength of alloy1 (15.41% Cr, 35.3% Fe) and alloy2 (15.08% Cr, 40.1% Fe) decreases with the increase in aging time. However, for alloy3 with high Fe content, the yield strength increases suddenly at 3000 h aging time due to the improving effect of solid solution strengthening. In addition, the dislocation movement mechanism of GH2107 alloy was studied, and Orowan bypass mechanism is more likely to occur in alloys with high Fe content. [ABSTRACT FROM AUTHOR]

The influence of microstructure evolution on the tensile properties of the novel nickel-based powder metallurgy superalloys after long-term aging at 800 ℃ for 100~5000 h was studied. The results show that the grain size of the alloys does not change significantly with the increase of aging time, and the grain boundaries are coarsened and appear the discontinuous “sawtooth”. Secondary γ′ phase particles obviously coarsen which conforms to the LSW theory. The content of TCP phases precipitated increases with the increase of aging time. After aging for 1000 h, the intermittent long white precipitates are observed at the grain boundary. After aging for 2000 h, a large number of elongate needle-like precipitates appear in the grain. The content of TCP phases reaches the maximum after aging for 5000 h. Due to the coarsening of the secondary γ′ phase, the tensile strength and plasticity of the alloys at 700 ℃ gradually decrease with increasing the aging time. The tensile fracture has the characteristics of necking and dimple, and the fracture shows the dimple fracture.

The current study emphasizes the impact of styrene-butadiene-styrene (SBS) molecular structures on the extent of performance deterioration in asphalt mixes after short-term and long-term laboratory aging. First, modified binders were prepared using linear (L-SBS), branched (B-SBS), high vinyl (HV-SBS), and di-block (DB-SB) SBS copolymers, and consequent asphalt mixes were fabricated using these modified binders. The influence of aging on the asphalt mixture performance has been evaluated through Cantabro mass loss, fracture properties, fatigue, and rut resistance behavior. Results showed that irrespective of the type of SBS polymer in the binder, the short-term aging (STA) of asphalt mixes had an insignificant effect on their performance properties. However, a substantial drop in all mix performances was observed after long-term aging (LTA) with L-SBS and B-SBS modified binders due to the degradation of the polymer chains. Mixes prepared with L-SBS and B-SBS copolymers depicted higher variation in the aging index after LTA than their counterparts and were also unable to protect the base binder from stiffening. In contrast, HV-SBS and DB-SB generate significantly lower temperature susceptibility in the asphalt mixture due to higher vinyl content (≥30%), i.e., location of the C=C group as the side chain in the butadiene segment. Fourier-transform infrared spectroscopy (FTIR) results reveal that the increase of carbonyl and sulphoxide compounds, and the lowering of polybutadiene compounds validate the adverse effect of LTA on L-SBS and B-SBS copolymers. On the contrary, such behavior was not reflected in HV-SBS and DB-SB copolymers. Thus, the current study presents the major limitation of using branched and linear SBS polymers having comparatively lower vinyl content, and recommends the mandatory use of high-vinyl SBS copolymers for ensuring enhanced long-term performance. [ABSTRACT FROM AUTHOR]

For China's second-generation aero-engine blade DD6 single-crystal high-temperature alloy, the standard solution-treated test rods were subjected to long-term aging experiments (1290 °C, 1 h + 1300 °C, 2 h + 1315 °C, 4 h air cooling + 1120 °C, 4 h air cooling + 870 °C, 32 h air cooling) at 980 °C for 1000 h, 5000 h, and 7500 h, and the effects of different long-term aging times on the organization evolution, phase precipitation morphology, high-temperature mechanical properties, and endurance performance of the alloy were studied. The results show that with the increase of aging time, the γ′ phase coarsens, joins along the <100> and <010> directions, and merges to form irregularly shaped directional growth and rafting. The endurance life shows a decreasing trend; at 980 °C/243 MPa, 980 °C/270 MPa, 980 °C/309 MPa for the alloys after 5000 h aging, the enduring life decreased by 47.97%, 70.98%, and 76.75%, and 81.25%, 73.18%, and 87.00% after 7500 h aging, respectively. The tensile strength of the alloy at 760 °C first decreases and then increases, with a minimum value at 5000 h; there is a gradual increase in elongation; there is a gradual decrease in tensile strength at 980 °C; and there is first an increase and then decrease in elongation, with a maximum value at 1000 h. This is due to the diffusion phenomenon of the elements in the alloy after 5000 h aging, the emergence of W-rich, Re-, Mo-, and Ni-poor phenomena, and the transformation of the μ-phase from needle-like to rod-like and block-like. [ABSTRACT FROM AUTHOR]

The morphological evolution of γ′ phase, the precipitation of TCP phases and the evolution of the interfacial dislocation networks in DD22 nickel-based single crystal superalloys with different Ru contents (3% and 5%, mass fraction) were investigated by transmission electron microscopy and field emission scanning electron microscopy during long-term aging at 1130 ℃. The results show that γ′ phase of 5Ru alloy are smaller in size and more regular in shape than that of 3Ru alloy. The mismatch of γ/γ′ phases is larger in 5Ru alloy, and the high content of Ru causes the reverse distribution of elements such as Re and Mo. During long-term aging at 1130 ℃, the coarsening rate, dissolution rate and rafting rate of γ′ phase in 5Ru alloy are lower than those of 3Ru alloy. There is still no TCP phase precipitation in 5Ru alloy after long-term aging for 1000 h, while a small amount of TCP phase is precipitated in 3Ru alloy after long-term aging for 50 h. With the prolongation of long-term aging time, the number and size of TCP phases both increase. Compared with 3Ru alloy, the interfacial dislocation networks of 5Ru alloy are denser and more regular after long-term aging for 1000 h. Above all, the reverse distribution of elements and low diffusion coefficient of Ru make 5Ru alloy exhibit higher microstructural stability than 3Ru alloy.

Hydrogen embrittlement (HE) behavior strongly threatens the safety of metallic structural materials. In this study, the HE resistance of Custom 465 maraging stainless steel is dramatically enhanced by long-term aging process. The influence of long-term aging on the hydrogen-assisted cracking behavior of the maraging stainless steel was thus unveiled using slow strain rate tensile test (SSRT), x-ray diffraction (XRD), and electron back-scattered diffraction (EBSD). The results showed that, compared with the peak-aged steel, the long-term aged (over-aged) ones possessed higher volume fraction of reversed austenite. A certain amount of austenite observed in the crack tips and microvoids of long-term aged steel acted as dual effective traps of both cracks and diffusible hydrogen atoms. Besides, the ripening of intermetallic η-Ni3Ti precipitates in long-term aged steel relaxed the stress concentration during SSRT and reduced the density of deleterious reversible hydrogen traps, which synergistically improved the cracking resistance of the matrix. The crystallographic orientation analysis of the hydrogen-induced cracks demonstrated that, in the long-term aged steel, higher fraction of low-angle grain boundaries (LAGBs) with lower kernel average misorientation (KAM) value and fraction of Σ3 coincidence site lattice (CSL) grain boundary favored the retardation of hydrogen-assisted crack propagation. [ABSTRACT FROM AUTHOR]

Impact toughness degeneration and microstructure evolution of alloy 617B during 650–725°C long-term aging for up to 12,000 h were investigated in present work. It is found that impact toughness decreases apparently even after just 20 h aging in the temperature range of 650–725°C and keeps decreasing with prolonging aging time. Hence, detailed microstructure observation and mechanical property tests were carried out to reveal the essence of impact toughness degeneration during long-term aging. And the reason is confirmed to be the combination effect of plasticity evolution and grain boundary carbide coarsening. The degeneration of impact toughness with prolonging aging time can be divided into rapid decrease stage, slow decrease stage and stable stage. The decrease of plasticity in the major reason for rapid impact toughness degeneration in the initial stage of aging. Grain boundary carbide coarsens obviously during aging and tends to be continuous. This is the major reason for the slow and continuous decrease of impact toughness in the slow decrease stage. Finally, plasticity and grain boundary carbide change little, resulting in the stable stage of impact toughness evolution. Enough attention should be paid on impact toughness degeneration in the evaluation of long-term stability.

Nickel-based single crystal superalloys CMSX-4 have been widely used to manufacture aeroengine turbine blades because of their excellent high-temperature comprehensive properties. The microstructure evolution behavior, mechanism, and influence on micromechanical behavior of the second-generation nickel-based single crystal superalloy during long-term aging at 950°C and 1050°C for 10–2000 h were investigated. The results show that, with the extension of aging time, the average size of γ' phase increased, whose morphology changed from square block to strip and L shape and rafting phenomenon was observed. The coarsening of γ' conforms to Lifshitz–Slyozov–Wagner (LSW) theory and the coarsening rates are 4.241×10−5 and 9.954×10−5μm3/h at 950°C and 1050°C, respectively. After aging at 950°C and 1050°C for 1000 h, segregation of refractory elements was formed in the samples. There are hard topological close-packed (TCP) phases surrounded by γ' envelope precipitates, which destroyed the continuous structure of γ'. The precipitation of TCP caused the depletion of refractory element Re in the γ' envelope phases, resulting in softening effect. It was also found that high temperature can not only accelerate the coarsening of γ' phase but also promote the precipitation and growth of TCP phases. • Aging at 950°C and 1050°C caused the coarsening and raft of γ' phase. • Secondary γ' phases precipitated during aging at 1050°C up to 2000 h. • High temperatures promoted precipitation and growth of TCP. • TCP caused the depletion of refractory elements in the γ' envelope phase. • The micromechanical inhomogeneity of γ' phase was discussed. [ABSTRACT FROM AUTHOR]

Lignin is abundant in nature. The use of lignin in the asphalt pavement industry can improve pavement performance while effectively optimizing pavement construction costs. The purpose of this paper is to study the effect of lignin on the anti-aging properties of asphalt. Commercial lignin was selected to prepare a lignin-modified asphalt binder. The properties of lignin-modified asphalt were studied by rheological experiments. The high-temperature rheological properties of two kinds of base asphalt and modified asphalt samples with different contents of lignin under three conditions of original, rolling thin film oven (RTFO) aging, and pressure aging vessel (PAV) were tested and analyzed with temperature sweep, frequency sweep, and multiple stress creep recovery (MSCR) tests. By comparing the variation laws of evaluation indicators, such as complex shear modulus G*, phase angle δ, anti-aging index, cumulative strain, and viscous component Gv, we found that lignin could effectively improve the high-temperature stability of base asphalt, but it had a negative impact on the compatibility issues of base asphalt. Meanwhile, lignin played a filling role in the base asphalt, and the increase in viscosity was the fundamental reason for improving the high-temperature stability of the base asphalt. The research results indicated that lignin could effectively improve the anti-aging performance of asphalt and play a positive role in prolonging the service life of pavement. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

For China’s second-generation aero-engine blade DD6 single-crystal high-temperature alloy, the standard solution-treated test rods were subjected to long-term aging experiments (1290 °C, 1 h + 1300 °C, 2 h + 1315 °C, 4 h air cooling + 1120 °C, 4 h air cooling + 870 °C, 32 h air cooling) at 980 °C for 1000 h, 5000 h, and 7500 h, and the effects of different long-term aging times on the organization evolution, phase precipitation morphology, high-temperature mechanical properties, and endurance performance of the alloy were studied. The results show that with the increase of aging time, the γ′ phase coarsens, joins along the and directions, and merges to form irregularly shaped directional growth and rafting. The endurance life shows a decreasing trend; at 980 °C/243 MPa, 980 °C/270 MPa, 980 °C/309 MPa for the alloys after 5000 h aging, the enduring life decreased by 47.97%, 70.98%, and 76.75%, and 81.25%, 73.18%, and 87.00% after 7500 h aging, respectively. The tensile strength of the alloy at 760 °C first decreases and then increases, with a minimum value at 5000 h; there is a gradual increase in elongation; there is a gradual decrease in tensile strength at 980 °C; and there is first an increase and then decrease in elongation, with a maximum value at 1000 h. This is due to the diffusion phenomenon of the elements in the alloy after 5000 h aging, the emergence of W-rich, Re-, Mo-, and Ni-poor phenomena, and the transformation of the μ-phase from needle-like to rod-like and block-like.

The chemical and rheological properties of terminal blend hybrid asphalt (TBHA) contributing to the consumption of waste tires before and after aging were studied. Styrene-butadiene-styrene (SBS) polymer, sulphur, crumb rubber (CR), and neat asphalt were chosen to prepare the TBHA. The short-term aging (STA) and long-term aging (LTA) of TBHA were simulated using a rolling thin film oven test (RTFOT) and pressure aging vessel (PAV), separately. The chemical and rheological properties of the TBHA were tested. The results show that the G* and G*/sin δ of TBHA ares generally lower than SBS-modified asphalt (SBSMA) at 76 °C, and the δ, Jnr0.1, and Jnr3.2 of TBHA are generally higher than SBSMA at 76 °C. Additionally, with the decrease of CR, the G* and G*/sin δ of TBHA decreased more obviously, and the G* and G*/sin δ of 5T_3S_0.2Sul (5 wt% CR, 3 wt% SBS, and 0.2 wt% sulphur) were the smallest. Moreover, during the STA, the SBS modifier in the TBHA degraded and made the bitumen predominantly soft; however, during the LTA, the hardening of the bitumen played a dominant role and increased its elasticity. The superior anti-aging properties of TBHA (both STA and LTA) are further demonstrated. [ABSTRACT FROM AUTHOR]

This study investigated the common aging protocols for binders and asphalt mixtures on fine aggregate matrix (FAM). Currently, no unified aging protocols are specified for laboratory-prepared FAM. The majority of FAM-related aging research used asphalt binders and mixture aging specifications. However, the practicality of employing these methods on FAM was not extensively examined. The rheological properties, chemical composition, and microstructure of aged binders extracted from FAM were extensively evaluated. For comparison, pressure aging vessel (PAV) aged binders and aged binders extracted from asphalt mixtures were similarly tested. Statistical analysis was performed on aging indices derived from test findings. Matching the aging level of FAM, aged binders, and asphalt mixtures required shortening the aging time for FAM under PAV aging or prolonging the aging time of loose mixes aging at 95°C during the early stages of aging. FAM's aging level was not statistically different from that of binders and mixtures under severe aging circumstances. The findings of this paper will be valuable in multiscale testing of asphaltic materials. [ABSTRACT FROM AUTHOR]

A series of long-term high-temperature aging tests of ASME A335-P92 steel from 1,000 to 29,000 h at 650°C were carried out. The microstructure evolution of as-received and aging specimens at different stages was investigated using optical microscope observations, scanning electron microscope examinations, and TEM investigations. The static mechanical strength properties (yield strength/ultimate tensile strength) at room and 600°C test temperatures and the plastic performance (elongation/reduction in area) were also analyzed. The experimental results show that the Laves phase can be precipitated rapidly in the early aging period. After a certain aging period, the continuous precipitation of M23C6 and the relatively high coarsening rate of Laves resulted in a rapid decrease of room and high-temperature mechanical properties in the early aging period. However afterwards for the long aging time, a slow decline in tendency of mechanical properties was presented.

Low-temperature pavement performance is important in freezing areas in northern climates. While agencies and contractors pursue efforts to add recycled asphalt materials (RAMs) into the mix design to reduce costs, the aged, stiffer material being blended in can dramatically alter the performance. A correlation between the Glover–Rowe parameter (G–R) and delta Tc (ΔTc) was developed in 2011 by Anderson et al. to relate the onset of nonload-related and significant cracking values. The relationship provides a correlation between nonload-related and low-temperature cracking properties of the binder. To further evaluate this relationship, four cold-region virgin binders from Wisconsin and Michigan were blended with varying percentages of RAM mixtures. Blends were then laboratory aged tested to obtain stiffness, m-value, complex shear modulus, and phase angle from BBR and DSR testing, allowing for the calculation of ΔTc and the G–R parameters. Investigation of their correlation for each binder source and the change in ΔTc was evaluated for each blend. Updated correlations and trends show that correlations are source dependent, suggesting that the ΔTc specification maxima should be re-evaluated for their inclusion of RAP sources. [ABSTRACT FROM AUTHOR]

Featured Application: This study provides guidelines for asphalt binder modifier selection to produce low modulus binders (softer binders) to meet desired quality. The research focuses on reducing expected cracking susceptibility of modified asphalt binders after long-term aging. The study recommends the development of engineered modifiers for specific paving applications. In recent years, increased use of recycled asphalt materials (RAP) has created a need for softer binders to compensate stiffer binder coming from RAP. Economic alternatives, like recycled oils and proprietary bio-based oils, can be potential modifiers that will reduce the dependence on petroleum-based alternatives. However, there is limited information on the long-term rheological performance of binders modified with proprietary modifiers. These modifiers are chemically complex and their interaction with binders further complicates the binder chemistry. Therefore, the objective of this study was to evaluate the impact of modifier chemistry on modified binders' long-term cracking potential. A base binder of Superpave Performance Grade (PG) 64-22 was used to develop PG 58-28 binder using six different modifiers. An unmodified PG 58-28 was included for a comparative analysis. A few modified binders rheologically outperformed the base binder and others performed similarly. The modifier derived from recycled engine oil showed the worst performance. Chemical analysis indicated that the best performing modified binders had significant amounts of nitrogen in the form of amines. On the other hand, poor performing modified binder had traces of sulfur. Additionally, modifiers with lower average molecular weights appeared to have a positive impact on the performance of aged binders. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the effect of long-term aging on electrochemical corrosion characteristics of austenitic AISI 304 steel. AISI 304 steel was subjected to aging treatment for an extended period at 700 °C up to a maximum of 10,000 h. The variation in the microstructure of aged specimens was observed with an optical microscope (OM) and a scanning electron microscope (SEM). The electrochemical polarization test was conducted to obtain the corrosion current density (Icorr) and corrosion potential (Ecorr). The metastable intermetallic M23C6 carbides generated in the vicinity of γ/γ grain boundaries and coarsened with aging time. The δ-ferrite island decomposed into σ-phase and M23C6 carbide with an aging time increase. As the aging time increased, the current density increased, but the corrosion potential of the austenitized specimen exhibited a minimum value of 0.04 μA/cm2. The highest pitting resistance exhibited at the austenitized specimen due to the absence of carbides. Consequently, the corrosion resistance of austenitic AISI 304 steel decreases with long-term aging time. The microstructural analyses well support this result. [ABSTRACT FROM AUTHOR]

Anodic titanium dioxide (TiO2) nanotubes were found to be active photocatalysts. These photocatalysts possess a high surface area, even when supported, rendering them potential candidates for water treatment. In this work, photocatalytic surfaces were produced by anodizing commercially pure Ti plates using two different electrolyte compositions and correspondingly diverse process parameters. Changes in the physical and chemical stability as well as photocatalytic activity were studied over a fifty-two-week aging process. During this period, the nanotubular surfaces were exposed to flowing synthetic greywater, solar irradiation, and the natural environment. The physical and phase stability of the materials anodized using the organic electrolyte were found to be outstanding and no degradation or change in crystalline structure was observed. On the other hand, materials anodized in the aqueous electrolyte proved to suffer from light-induced phase transition from anatase to rutile. Surfaces synthesized in the organic electrolyte were more resistant to fouling and showed a better tendency to recover photocatalytic activity upon cleaning. In conclusion, the nanotubes produced in the organic electrolyte proved to be stable, rendering them potentially suitable for real-life applications.

Abstract The microstructure evolution of 617B superalloy especially the dissolution behavior of intragranular M 23 C 6 carbide has been investigated after aging at 700 °C and 750 °C up to 12000 h utilizing a combination of field emission scanning electron microscope (FESEM), electronic probe microanalysis (EPMA), transmission electron microscope (TEM), and precise chemical analysis. During long-term aging process, the γ′ phase precipitates and coarsens gradually. The M 23 C 6 carbide distributes on the grain boundaries as well as within the grains, which performs different evolution behavior. The M 23 C 6 carbide on the grain boundaries coarsens to films and a γ′ phase layer forms at the M 23 C 6 /γ interface. However, the M 23 C 6 carbide within the grains dissolves partially into the matrix resulting in different morphologies of phase boundary. Furthermore, mutual diffusion relationship of alloying element among γ′ phase, M 23 C 6 carbide (both on the grain boundaries and within the grains) and the γ matrix during long-term aging process has been established based on precise micro-chemical analysis. Graphical abstract Image 1 Highlights • Microstructure evolution of alloy 617B is investigated at 700 °C and 750 °C up to 12000 h. • The intragranular M 23 C 6 carbide particle dissolves partially into the matrix. • The grain boundary M 23 C 6 carbide coarsens to films accompanied with formation of γ′ layer at the carbide/γ interface. • Element mutual diffusion relationship and elements redistribution among phases is established. [ABSTRACT FROM AUTHOR]

Abstracts Microstructure evolution of alloy 740H for advanced ultra-supercritical (AUSC) power plants are studied during long term aging with a temperature scope of 600–720 °C up to 10,000 h and 800 °C up to 2000 h. Field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM) and micro-chemical phase analysis are carried out for detailed investigation of phase evolution. Though phase morphology does not change dramatically during 720 °C aging, apparent element redistribution are detected after 200 h aging. Different from common knowledge, decomposition of MC carbide is detected during aging. Element redistribution relationship between γʹ phase, MC carbide and M 23 C 6 carbide during 10,000 h aging is established based on quantitative analysis and morphology observation. Nb, Ti and C elements are released into matrix during decomposition of MC carbide. Nb and Ti elements diffuse into γ′ phase during growth of γ′ particles and Cr element is rejected out of the phase. The abundant C element released by MC carbide and Cr element rejected from γʹ phase are beneficial for growth of M 23 C 6 carbide and weight fraction of M 23 C 6 carbide doubles after 720 °C/10,000 h aging. This time-consuming and element diffusion related process can be modified into the reaction: MC+γ→(MC) t +γ′+(Cr) enrichment →M 23 C 6 +γ′. The evolutions of different phases are linked by redistribution of elements during long thermal exposure. Graphical abstract Image 1 Highlights • Microstructure evolution of alloy 740H is studied at 600–800 °C for 10,000 h. • Decomposition of MC carbide is detected. • Element redistribution relationship between phases is established. • Element interaction between phases should be taken into consideration for better stability control. [ABSTRACT FROM AUTHOR]

A dynamic time evolution method is developed in this paper to implement concurrent device-circuit aging simulations. The dynamic stress on each device during operations is processed by an equivalent stress duration concept, which transfers a continuous-time-based reliability model to its incremental version. With it, the device aging parameters such as threshold voltages are calculated by implementing a given reliability equation inside a compact model. The method is implemented into an open source circuit simulator for function verifications. Aging feedback, which slows down the further aging, is naturally included. Circuit aging simulations show that an overestimation of 32% can be avoided compared to those without considering the aging feedback. [ABSTRACT FROM AUTHOR]

In recent years, increased use of recycled asphalt materials (RAP) has created a need for softer binders to compensate stiffer binder coming from RAP. Economic alternatives, like recycled oils and proprietary bio-based oils, can be potential modifiers that will reduce the dependence on petroleum-based alternatives. However, there is limited information on the long-term rheological performance of binders modified with proprietary modifiers. These modifiers are chemically complex and their interaction with binders further complicates the binder chemistry. Therefore, the objective of this study was to evaluate the impact of modifier chemistry on modified binders’ long-term cracking potential. A base binder of Superpave Performance Grade (PG) 64-22 was used to develop PG 58-28 binder using six different modifiers. An unmodified PG 58-28 was included for a comparative analysis. A few modified binders rheologically outperformed the base binder and others performed similarly. The modifier derived from recycled engine oil showed the worst performance. Chemical analysis indicated that the best performing modified binders had significant amounts of nitrogen in the form of amines. On the other hand, poor performing modified binder had traces of sulfur. Additionally, modifiers with lower average molecular weights appeared to have a positive impact on the performance of aged binders.

Abstract The phase transformation characteristics of alloy 617B are investigated in the temperature range of 600–800 °C for up to 10000 h using a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and precise chemical analysis. The γ′ phase is stable during 600–720 °C aging but degenerates quickly at 800 °C. The M 23 C 6 carbide shows a plate-like shape and has a cube-on-cube orientation relationship with the γ matrix. The chemical composition and lattice parameter of phases are determined by precise chemical analysis. The phase evolution is an element diffusion-related process, and the element redistribution relationship is established here. In the precipitation and coarsening process, the γ′ phase absorbs the elements Al and Ti and rejects Cr and Mo elements into the matrix. M 23 C 6 carbide is confirmed by chemical analysis to be rich in Cr and Mo. The rejected Cr and Mo elements from the γ′ phase can transfer into M 23 C 6 carbide during the coarsening of M 23 C 6 carbide. In addition, the Mo- and Cr-rich μ phase is detected, and the precipitation of the μ phase competes with M 23 C 6 carbide for Mo and Cr. Hence, the interaction between phases should be taken into consideration for better control of microstructure stability in the alloy 617B. Highlights • Microstructure evolution of alloy 617B is investigated at 600–800 °C for 10,000 h. • Phase evolution is studied by a combination of SEM, TEM and precise micro-chemical analysis. • Element redistribution relationship between phases is established. • Interaction between phases should be taken into consideration for better stability control. [ABSTRACT FROM AUTHOR]

The effect of long-term isothermal aging of Haynes 230 super-alloy in an advanced ultra-supercritical (A-USC) power plant at 700 °C for up to 10,000 h on microstructural evolution and tensile behavior. And utilizing a combination of the scanning electron microscope (SEM), X-ray diffraction analysis (XRD), and transmission electron microscope (TEM). Although the grain size and grain boundary M23C6 carbides did not change significantly, the dissolution of intercrystallite primary M 6 C carbides and the precipitation of intracrystalline secondary lamellar M 6 C carbides were observed at 2000 h to 10,000 h. According to the SEM and TEM results, it is shown that the dissolution of primary M 6 C carbides makes the W, Mo, and Cr in the γ matrix increase, while the precipitation process of secondary M 6 C carbides is M+ 6 C→M 6 C. To reduce the interfacial energy of the γ matrix, secondary M 6 C carbides are precipitated in the crystal under long-term aging at 700 °C, with a gradual increase in time content. the best tensile and yield strengths at 750 °C occur after 4000 h of aging, with microscopic voids forming mainly around the granular M 6 C carbides in the crystal, but the solid solution strengthening effect of the matrix provides the strength. The worst strength and elongation occur after 10000 h aging, when the dissolution of granular M 6 C and secondary precipitation of M 6 C carbides are most abundant, interfacial cavity formation of granular M 6 C carbides and brittle fracture of M 6 C carbide particles, and the growth of non-co-grained secondary M 6 C carbides with the matrix allow more microscopic cavities to appear during high-temperature tension, reducing the strength of Haynes 230 and plasticity. • Phase precipitation behavior of Haynes 230 was investigated during long-term aging at 700 ℃. • Precipitation processes of secondary lamellar-like M 6 C carbide were clarified. • Dissolution of primary granular M 6 C carbides was discussed. • Variation in mechanical properties is divided into several stages. • The relationship between precipitation processes and mechanical properties was established. [ABSTRACT FROM AUTHOR]

Ni-base superalloys are materials which are designed to resist extreme thermal and mechanical conditions. In this regard, an essential factor is their microstructure consisting of γ ′ precipitates embedded in a γ matrix. The application of superalloys at high temperatures can however induce the topological phase inversion, where the γ ′-phase topologically becomes the matrix phase, resulting in subpar material properties. In this work, the topological inversion is analyzed via experiment and phase-field simulation. The evolution of the microstructure has been quantified in the second generation single crystal Ni-base superalloy ERBO/1, which belongs to the family of CMSX-4, submitted to long-term aging at 1100 ° C for up to 250 h. Phase-field simulations carried out using a multi phase-field approach deliver insight into the microstructure evolution driven by the loss of coherency of the γ ′ precipitates, which is induced by the accumulation of dislocations at the γ / γ′ interfaces. The obtained simulation results are in good agreement with the experimental results, and indicate that the mechanisms causing the topological inversion are linked to the accommodation of the lattice misfit, which enables coalescence and ripening of γ′ precipitates. [ABSTRACT FROM AUTHOR]

The corrosion properties of a 22.5 wt. (%) Cr duplex stainless steel were investigated after long-term aging of 3000, 5000 and 7000 hours at 300 and 400 ºC. The corrosion resistance was measured based on mass loss in a FeCl3 10 wt. (%) solution and electrochemical measurements in a 0.1 M H2SO4 solution. The results indicate that the corrosion resistance decreased steadily up to 5000 hours of aging. However, the samples subjected to 7000 hours of aging showed better corrosion resistance than those aged for 3000 and 5000 hours. This effect is attributed to the phase transformation that occurs during aging, a finding which was confirmed by hardness, transmission electron microscopy and X-ray photoelectron spectroscopy measurements.

Three experimental single crystal superalloys with 0%Nb, 0.5%Nb, 1.0%Nb were cast in the directionally solidified furnace, while other alloying element contents were basically kept unchanged. The effect of Nb on the microstructure, stability at 1100 °C and stress rupture properties at 1070 °C and 160 MPa of the single crystal superalloy were investigated. The experiment results show that the primary dendrite arm spacing decreases and the volume fraction of γ/ γ′ eutectic of the alloy increases with the increase of Nb content in the as-cast microstructures. The size of γ′ phase particles becomes small and uniform and the cubic shape does not obviously change with the increase of Nb content. The precipitating rate and volume fraction of TCP phases increase significantly with the increase of Nb content in the process of long term aging at 1100 °C. The stress rupture lives increase and elongation decreases with increasing Nb content at 1070 °C/160 MPa. At last, the relationship between the microstructures stability, stress rupture properties of the alloy and Nb content is discussed based on JMatPro software and the lastest relevant database for single crystal superalloy. [ABSTRACT FROM AUTHOR]

The objective of this study is to evaluate the long-term aging effect on the rheological properties of the modified PG 76-22/PG 76-16 binders produced from ground tire rubber (GTR) with various polymers after a long-term aging process. The tests included the investigation of G*sin δ, phase angle, amplitude sweep, frequency sweep, creep and creep recovery and stress relaxation in terms of three base binders and five polymers. The test results indicated that both base binder and polymer type affect the fatigue resistance, creep and creep recovery, viscoelastic property, and relaxation characteristic of each modified binder. In addition, terminally blended GTR binder has better fatigue resistance than laboratory blended GTR binder after a long-term aging procedure in this study. It seems that binders modified with polyphosphoric acid combined with 7% GTR exhibit more elastic properties and better rheological properties than other modified binders regardless of binder sources. [ABSTRACT FROM AUTHOR]

Effect of thermal aging at 350 °C for 3000 h on near-threshold fatigue crack growth (FCG) behavior of a Ni–Cr–Mo–V steel welded joint was investigated at various load ratios, R . FCG resistance of base metal after long-term aging was decreased and found to be dominated by microstructure influence; whilst FCG was controlled by R in weld metal due to microstructure homogeneity. Degradation of FCG threshold was assessed using a quantitative parameter. A microscopic interpretation of FCG threshold showed the predominant role of characteristic microstructure size. A model for fatigue threshold prediction involving the long-term aging effect was developed, and able to evaluate the stability of near-threshold FCG resistance of the welds in case of long-term service exposure. [ABSTRACT FROM AUTHOR]

The microstructure evolution in directionally solidified Ni-based superalloys DZ411 with different Tantalum (Ta) contents (2.72, 3.10, and 4.00 wt%) was investigated. After directional solidification, three alloys with different Ta contents were subjected to standard heat treatment: solution treatment (1230 °C/2 h/AC)+ primary aging (1120 °C/2 h/AC)+ secondary aging (870 °C/24 h/AC). Then, following isothermal long-term aging treatments were performed at 950 °C for 50, 100, 200, 500 and 1000 h. The addition of Ta can lead to the increase of the volume fractions of MC carbides, eutectics, and γ′ phases during directional solidification. In addition, with the increase of Ta content, the mismatch of γ/γ′ increases, thus, the shape of γ′ becomes more regular. After solution heat treatment, the MC carbides are decomposed, and more M 23 C 6 carbides are precipitated along the grain boundaries in alloys with increasing Ta contents. Besides, the eutectic cannot be completely eliminated. After secondary aging, more secondary γ′ phases are precipitated on the γ matrix channels in alloys with increasing Ta contents. Furthermore, the addition of Ta can delay the coalescence of the γ′ phase during long-term aging, which can be attributed to the reduction of the coarsening rate K according to the precipitation coarsening theory of Lifshitz and Slyozov and Wanger (LSW). • The content of Ta is increased on the basis of DZ411 alloy. • The effect of Ta on the cubicity of γ′ phase is studied. • The effect of Ta on coarsening behavior of γ′ phase during long-term aging is illustrated. [ABSTRACT FROM AUTHOR]

• Evolution of Microstructure of Alloy Aged at 800 °C for 100–10000 h. • A new method of identifying TCP phase. • Three-dimensional characterization of microstructure. The microstructure stability, evolution law and identification of carbide and harmful phase TCP of nickel-base powder superalloy aged at 800 ℃ for 100 h —10000 h were studied by means of field emission scanning electron microscope, atomic force microscope and electron backscatter diffraction. The results show that with the increase of aging time, the grain size changed little, the grain boundary coarsened and the twin boundary Σ3 increased first and then decreased. γ' phase coarsened obviously from 500 h aging, and the coarsening rate increased first and then decreased The coarsening mechanism is mainly the combination of adjacent γ' phase by AFM analysis. Lath-like σ phase CrCo precipitated at the grain boundary first after aging for 1000 h. When the aging time was up to 2000 h, the needle-like μ phase Co 7 (W, Mo) 6 was observed in the crystal. With the further increase of aging time, the total content of TCP phase at grain boundary and in crystal increased obviously. However, at 10000 h, the TCP phase in the crystal and at the grain boundary almost disappeared, mainly because the atoms in the TCP phase diffused into the γ' phase to form a new solid solution and deposited on the grain boundary, which further coarsened the grain boundary. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine effects of aging methods (wet-aged, dry-aged, and packaged dry-aged) during 60 d on quality traits and microbial characteristics of beef. Wet-aged beef was packed by vacuum packaging and stored in a 4°C refrigerator. Dry-aged beef was used without packaging. Packaged dry-aged beef was packaged in commercial bags. Dry-aged and packaged dry-aged samples were stored in a meat ager at 2°C-4°C with 85%-90% relative humidity. Meat color, crust thickness, aging loss, cooking loss, Warner-Bratzler shear force (WBSF), texture profile analysis, Torrymeter, meat pH, water activity, volatile basic nitrogen (VBN), thiobarbituric acid reactant substances (TBARS), and microbial analysis were measured or performed every 15 d until 60 d of aging time. Meat color changed significantly with increasing aging time. Differences in meat color among aging methods were observed. Aging losses of dry-aged and packaged dry-aged samples were higher than those of wet-aged samples. Wet-aged beef showed higher cooking loss, but lower WBSF than dry-aged and packaged dry-aged beef. VBN and TBARS showed an increasing tendency with increasing aging time. Differences of VBN and TBARS among aging methods were found. Regarding microbial analysis, counts of yeasts and molds were different among aging methods at the initial aging time. Packaged dry-aged and dry-aged beef showed similar values or tendency. Significant changes occurred during aging in all aging methods. Packaged dry aging and dry aging could result in similar quality traits and microbial characteristics of beef., Competing Interests: The authors declare no potential conflicts of interest., (© Korean Society for Food Science of Animal Resources.)