Early Stage Of Aging Research Articles

Effect of Static Aging on Mechanical Properties of an 18Cr-8Ni-W-Nb-V-N Stainless Steel

The interrelations between microstructure, precipitation and mechanical properties of the 18Cr-8Ni-W-Nb-V-N austenitic stainless steel were examined under long-term aging at 650°C. It was shown that aging leads to decreasing strength characteristics with increasing aging time despite the fact that hardness tends to increase. In none-aged condition the present steel exhibits superior impact toughness of about 255 J/cm-2. This values decreases gradually at the early stage of the aging. After 1000 hours exposure the impact toughness is 195 J/cm-2 and decreases sharply to 135 J/cm-2 at 3000 hours. However, an evidence for ductile fracture was found even after long-term aging. Degradation in impact toughness and mechanical properties with aging is discussed in relation to microstructure evolution, precipitations of the secondary phase and fracture mechanisms.

Moisture diffusivity of early age concrete considering temperature and porosity

A series of experiments and numerical analyses have been carried out to derive a model of the moisture diffusion coefficient in concrete structures. The moisture diffusion coefficient generally depends on the relative humidity and temperature as well as the age of concrete, because microstructures of concrete develop with aging, especially in the early stage of aging. Therefore, the modified model of the moisture diffusion coefficient proposed here takes these three parameters into consideration. Experiments on moisture diffusion were performed to investigate the variation of the moisture diffusion coefficient with age and temperature under three temperature conditions (20, 50, and 80°C). Based on the experimental results, a new model of the moisture diffusion coefficient considering the aging and temperature was developed by a numerical inverse analysis. As it considers porosity, humidity, and temperature, beyond the existing model for hardened concrete, the suggested diffusion coefficient model is applicable to early age concrete.

UV Ageing Test and EIS Study of Fluorocarbon Resin Coatings on Galvanized Sheet

The aim of this study is to study the protection performance of fluorocarbon resin coatings on galvanized sheets with electrochemical impedance spectra(EIS) and scanning electron microscopy (SEM) for UV ageing to simulate nature environment. The results indicated that impedance of the coatings acted as a capacitive character at the early UV ageing stage. the diffusion impedance was shown in low-frequency range, which was attributed to the self-healing effect of the chromate layer to the metal interface. After 2000 hours of ageing in the UV chamber, there is a low impedance values in the impedance spectra. Taking into account defects were found on the film surface on SEM picture, it is easy that the outside corrosive substances meet metal substrate through the coating at the defects.

HRTEM Observation of Early Stage of Precipitation in Mg-Gd-Y Alloys

HRTEM observation was performed to clarify the early stage of precipitation in Mg-Gd-Y alloy aged at 473 K. The hardness increased with increasing aging time after quenching. The hardness increased slowly at early stage of aging, increased rapidly, and then reached to peak hardness. At as-quenching and the early stage of aging, the weak spots appeared at a half 100Mgin SAED pattern. The intensity of these weak spots changed to higher with increasing aging time. Monolayers on {100}Mgplanes and β” phase existed at this aging stage. Monolayers, β” phase, the precipitates with five layers corresponding the feature of (020)β’plane and β’ phase co-existed after the rapidly increasing of hardness. In the peak aged specimen at 473 K, both of β” and β’ phases co-existed and β’ phase were formed dominantly.

Isothermal Decomposition of Ferrite in a High-Nitrogen, Nickel-Free Duplex Stainless Steel

The formation and crystallography of second phases during isothermal decomposition of ferrite (α) in a high-nitrogen, nickel-free duplex stainless steel was examined by means of transmission electron microscopy (TEM). At an early stage of aging, the decomposition of α started along the α/γ phase boundaries where sigma (σ) phase and secondary austenite (γ2) precipitated in the form of an alternating lamellar structure. The combined analyses based on the simulation of diffraction patterns and stereographic projection have shown that most of the σ phase was related to the γ2 by the following relation: \( (111)_{\gamma } \parallel (001)_{\sigma } \) and \( [10\bar{1}]_{\gamma } \parallel [110]_{\sigma } . \)The intergranular and intragranular precipitation of Cr2N with trigonal structure were identified, and the orientation relationships (ORs) with α and γ matrix could be expressed as \( \left( {110} \right)_{\alpha } \parallel \left( {0001} \right)_{{{\text{Cr}}_{2} {\text{N}}}} \),\( \left[ {\bar{1}11} \right]_{\alpha } \parallel [\bar{1}100]_{{{\text{Cr}}_{2} {\text{N}}}} \,;\,(111)_{\gamma } \parallel (0001)_{{{\text{Cr}}_{2} {\text{N}}}} \), and \( \left[ {\bar{1}10} \right]_{\gamma } \parallel \left[ {\bar{1}100} \right]_{{{\text{Cr}}_{2} {\text{N}}}} , \) respectively. The precipitation of intermetallic χ phase was also observed inside the α matrix, and they obeyed the cube-on-cube OR with the α matrix. Prolonged aging changed both the structure of matrix and the distribution of second phases. The γ2, formed by decomposition of α, became unstable because of the depletion of mainly N accompanied by the formation of Cr2N, and it transformed into martensite after subsequent cooling. As a result, the microstructure of the decomposed α region was composed of three kinds of precipitates (intermetallic σ,χ, and Cr2N) embedded in lath martensite.

Effects of early-stage aging on locomotor dynamics and hindlimb muscle force production in the rat

Attenuation of locomotor function is common in many species of animals as they age. Dysfunctions may emerge from a constellation of age-related impairments, including increased joint stiffness, reduced ability to repair muscle tissue, and decreasing fine motor control capabilities. Any or all of these factors may contribute to gait abnormalities and substantially limit an animal's speed and mobility. In this study we examined the effects of aging on whole-animal locomotor performance and hindlimb muscle mechanics in young adult rats aged 6-8 months and 'early aged' 24-month-old rats (Rattus norvegicus, Fischer 344 × Brown Norway crosses). Analyses of gaits and kinematics demonstrated that aged rats moved significantly more slowly, sustained longer hindlimb support durations, moved with a greater proportion of asymmetrical gaits, were more plantigrade, and moved with a more kyphotic spinal posture than the young rats. Additionally, the external mechanical energy profiles of the aged animals were variable across trials, whereas the younger rats moved predominantly with bouncing mechanics. In situ analyses of the ankle extensor/plantar flexor muscle group (soleus, plantaris, and medial and lateral gastrocnemii) revealed reduced maximum force generation with aging, despite minimal changes in muscle mass. The weakened muscles were implicated in the degradation of hindfoot posture, as well as variability in center-of-mass mechanics. These results demonstrate that the early stages of aging have consequences for whole-body performance, even before age-related loss of muscle mass begins.

Age-hardening behavior, microstructural evolution and grain growth kinetics of isothermal ω phase of Ti–Nb–Ta–Zr–Fe alloy for biomedical applications

Age-hardening behavior, microstructural evolution and the grain growth kinetics of isothermal ω during aging treatments of Ti–25Nb–10Ta–1Zr–0.2Fe alloy were investigated. The results showed that in addition to martensite α″, a small amount of α and athermal ω was observed in the β matrix after solution treatment. The decomposition of martensite α″ and the transformation from athermal ω (ωath) to isothermal ω (ωiso) occurred at the early stage of aging. ωiso firstly competed to grow with α phase, and then dissolved and transformed into α phase. The growth and dissolution of ωiso was accelerated with increasing aging temperature. Finally, the α + β stable microstructure was obtained after aging for 280, 200, 24 and 2 h at 623, 673, 743 and 773 K, respectively. The alloy showed stronger age-hardening response at intermediate temperatures of 673 and 743 K, while exhibited weaker age-hardening response at lower temperature of 623 K and higher temperature of 773 K. The uniform distribution of dense ωiso and α precipitates in the β matrix with moderate size resulted in the peak micro-hardness values. The grain growth of ωiso obeys an asymptotic law, and the grain-growth exponent, n, was computed to be in the range of 0.23–0.26 at temperatures in the range of 623–743 K. The activation energy for ωiso grain growth, Qg was calculated to be 119.7 kJ/mol.

Effect of hot-air aging on properties of EPDM/SmBO3/EAA and EPDM/ATO/EAA composites

Ethylene–propylene–diene monomer (EPDM) rubber/samarium borate (SmBO3)/ethylene acrylic acid (EAA) and EPDM/sb in Sb-doped SnO2 (antimony tin oxide)/EAA composites are aged at 150°C for different intervals. It is found that alkaline SmBO3 can lower the oxidation rate of EPDM composites by scavenging acids formed during aging. The grown acrylic acid content lowers the pH level of EPDM composites and then elevates the oxidation rate. For EPDM/filler control, the chain scission dominates in the early stage of aging, while cross-linking takes the main effect in the latter stage of aging. Moreover, the poly (circular acid anhydride) formed by carboxylic acid in EAA during curing decomposes and influences the overall chemical cross-link points. The lowest crystallinity of EAA in EPDM/filler/EAA composites appears at the 10th day of aging and is attributed to the varied cross-link density. The changing trend of tensile strength is well consistent with that of swelling ratios, and electric properties are correlated with increased polar groups and crystallinity.

Effects of aging on the microstructure of a Cu-Al-Ni-Mn shape memory alloy

The influence of aging on the microstructure and mechanical properties of Cu-11.6wt%Al-3.9wt%Ni-2.5wt%Mn shape memory alloy (SMA) was studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometer, and differential scanning calorimeter (DSC). Experimental results show that bainite, γ2, and α phase precipitates occur with the aging effect in the alloy. After aging at 300dgC, the bainitic precipitates appear at the early stages of aging, while the precipitates of γ2 phase are observed for a longer aging time. When the aging temperature increases, the bainite gradually evolves into γ2 phase and equilibrium α phase (bcc) precipitates from the remaining parent phase. Thus, the bainite, γ2, and α phases appear, while the martensite phase disappears progressively in the alloy. The bainitic precipitates decrease the reverse transformation temperature while the γ2 phase precipitates increase these temperatures with a decrease of solute content in the retained parent phase. On the other hand, these precipitations cause an increasing in hardness of the alloy.

The influence of solution treatment temperature on microstructure and corrosion behavior of high temperature ageing in 25% Cr duplex stainless steel

In 25% Cr duplex stainless steels, the effect of prior-solution treatment temperature (STT) on the microstructure and corrosion behavior with ageing at 750 °C and 850 °C was investigated. The results revealed that the precipitation rate of σ-phase was fast in the early stage of ageing for 80 min, and then got slower with ageing time up to 330 min. The σ-phase formation was effectively suppressed by raising STT from 1060 °C to 1230 °C especially for ageing at 750 °C. Consequently, the corrosion rate of specimen was dependent on the amount of σ-phase precipitation, and was lowered due to higher STT, and more σ-phase precipitation can lead to the transition from metastable to stable pitting with ageing at 750 °C up to 330 min. Pitting occurred easily around coarse σ precipitates and caused selective dissolution in ferrite. The longer ageing time increased intergranular corrosion (IGC) susceptibility, whereas higher STT contributed to better resistance to IGC.

Genetic polymorphisms of multiple DNA repair pathways impact age at diagnosis and TP53 mutations in breast cancer

Defective DNA repair may contribute to early age and late stage at time of diagnosis and mutations in critical tumor suppressor genes, such as TP53 in breast cancer. Using DNA samples from 436 breast cancer cases (374 Caucasians and 62 African-Americans), we tested these associations with 18 non-synonymous single-nucleotide polymorphisms (nsSNPs) in four DNA repair pathways: (i) base excision repair: ADPRT V762A, APE1 D148E, XRCC1 R194W/R280H/R399Q and POLD1 R119H; (ii) double-strand break repair: NBS1 E185Q and XRCC3 T241M; (iii) mismatch repair: MLH1 I219V, MSH3 R940Q/T1036A and MSH6 G39E and (iv) nucleotide excision repair: ERCC2 D312N/K751Q, ERCC4 R415Q, ERCC5 D1104H and XPC A499V/K939Q. Younger age at diagnosis (<50) was associated with ERCC2 312 DN/NN genotypes [odds ratio (OR) = 1.76; 95% confidence interval (CI) = 1.10, 2.81] and NBS1 185 QQ genotype (OR = 3.09; 95% CI = 1.47, 6.49). The XPC 939 QQ genotype was associated with TP53 mutations (OR = 5.80; 95% CI = 2.23, 15.09). There was a significant trend associating younger age at diagnosis (<50) with increasing numbers of risk genotypes for ERCC2 312 DN/NN, MSH6 39 EE and NBS1 185 QQ (P(trend) < 0.001). A similar significant trend was also observed associating TP53 mutations with increasing numbers of risk genotypes for XRCC1 399 QQ, XPC 939 QQ, ERCC4 415 QQ and XPC 499 AA (P(trend) < 0.001). Our pilot data suggest that nsSNPs of multiple DNA repair pathways are associated with younger age at diagnosis and TP53 mutations in breast cancer and larger studies are warranted to further evaluate these associations.

Modeling of the Precipitation Kinetics During Aging a Predeformed Fe-Cu Alloy

A model is developed to describe the microstructure evolution during aging a Fe-Cu alloy. The precipitation process during aging a predeformed Fe-1.5 wt pct Cu is calculated and the kinetic details of aging are discussed. The model is satisfactorily tested by comparing with the reported experimental results. The numerical results demonstrate that the nucleation of the precipitates occurs on dislocations first. However, the maximum nucleation rate of the precipitates in the matrix is much higher than that on dislocations and it is not affected by the appearance of dislocations. Only a small fraction of precipitates locate on dislocations immediately after nucleation. The particles in the matrix dissolve preferentially during coarsening, and most of the remained precipitates locate on dislocations in an overaged sample. Dislocations have little effect on the number density and average radius of the precipitates in the late stage of aging, although they promote the beginning of precipitation in the early stage of aging. The heating rate of the specimen almost does not affect the summit of the particle number density as well as its corresponding mean particle radius.

저온 소성한 MgO 분말을 혼입한 시멘트 복합체의 기초 물성

The volume change in concrete takes place with changes in temperature and water content immediately after concrete casting. In the early age stage, the thermal and drying shrinkages can cause cracks that are very crucial to the durability of concrete. It was reported that when the cement with lightly-burnt MgO powder was used, the shrinkage of concrete can be reduced. This study investigates fundamental properties of cement composites with lightly burnt MgO powder by performing various experiments. The stability test results verified that MgO powder in cement composites does not cause any abnormal expansion. Also, the hydrate product analysis results obtained from MgO cement paste showed that MgO powder reduces the shrinkage at the longterm ages. In addition, the cement composites containing the proper amount of MgO powder could improve compressive strength. Finally, the shrinkage reduction from using MgO powder can be optimized by increasing MgO replacement level and curing temperature.

Strengthening behavior of Fe–Cr–Ni–Al–(Ti) maraging steels

In the present work a Ti-free and Ti-containing stainless maraging steel of type PH13-8 Mo were investigated with respect to their mechanical properties. Particular attention was given to the stress–strain behavior during tensile tests in correlation to the developed precipitates and austenite at differently aged conditions. Both alloys show a strong increase in strength from the very beginning of aging with the typical stress–strain behavior of maraging steels, whereas the Ti-containing alloy suffers from severe intergranular embrittlement at short aging times. Embrittlement of the Ti-containing steel grade is attributed to the significantly higher volume fraction of precipitates in the early stages of aging when compared to the Ti-free steel grade. Overaging leads to distinct work hardening in the Ti-containing alloy, which is caused by the evolution of the precipitates and the formation of reverted austenite.

Lattice Rectification in Atom Probe Tomography: Toward True Three-Dimensional Atomic Microscopy

Atom probe tomography (APT) represents a significant step toward atomic resolution microscopy, analytically imaging individual atoms with highly accurate, though imperfect, chemical identity and three-dimensional (3D) positional information. Here, a technique to retrieve crystallographic information from raw APT data and restore the lattice-specific atomic configuration of the original specimen is presented. This lattice rectification technique has been applied to a pure metal, W, and then to the analysis of a multicomponent Al alloy. Significantly, the atoms are located to their true lattice sites not by an averaging, but by triangulation of each particular atom detected in the 3D atom-by-atom reconstruction. Lattice rectification of raw APT reconstruction provides unprecedented detail as to the fundamental solute hierarchy of the solid solution. Atomic clustering has been recognized as important in affecting alloy behavior, such as for the Al-1.1 Cu-1.7 Mg (at. %) investigated here, which exhibits a remarkable rapid hardening reaction during the early stages of aging, linked to clustering of solutes. The technique has enabled lattice-site and species-specific radial distribution functions, nearest-neighbor analyses, and short-range order parameters, and we demonstrate a characterization of solute-clustering with unmatched sensitivity and precision.

Electroluminescence measurements of low-density polyethylene (LDPE) films subjected to high electrical stresses in different gas environments

It has been proposed that the measurement of the characteristics of electroluminescence (EL) observed during the application of ac and dc electric fields across thin films of polymeric material can be used to probe the early stages of electrical ageing. Both EL and electrical ageing of the polymer are thought to arise due to the injection of charge carriers into the material from the metallic electrodes. However, before changes in the EL characteristics can be properly assigned to polymeric ageing, it is necessary to understand the physical processes that give rise to EL. In this paper, the effect of absorbed gases N2 and SF6 on the EL characteristics of low density polyethylene were examined. It was found that the EL can be split into two different spectral components, C1, having a broad peak centered at a wavelength between 550 and 600 nm, and a second component, C2, having a peak wavelength greater than 700 nm. The intensity of the C1 component of EL was found to depend on the type absorbed gas present in the material while the intensity of the C2 component was found to be independent. The results demonstrate that the electronegativity of the absorbed gas plays a fundamental role in the formation of excited states and subsequent recombination in the case of the C1 emission while the C2 emission supports the conjecture that this is due to the excitation of surface plasmons at the dielectric/polymer interface.

Natural ageing of Al–Cu–Mg revisited from a local perspective

Although Al alloys based on the Al–Cu–(Mg) system have been investigated for decades, information about the evolution of microstructure on the atomistic level during natural ageing is scarce. Therefore, the early stages of natural ageing in laboratory Al–Cu–(Mg) alloys and in AA2024 were investigated using positron annihilation and X-ray absorption spectroscopy. This complementary approach allows for accessing both essential components of Al alloys, namely vacancies and alloying elements. It is found, that during natural ageing the chemical environment of vacancies is formed both of Cu and Mg atoms and that the rearrangement of vacancy surroundings persists the hardness increase of Al–Cu–Mg alloys. During natural ageing two different regimes of vacancy environment are detected and interpreted in terms of cluster growth and vacancy capture. Features of the near edge structure of the X-ray absorption are interpreted using theoretical calculations obtained by the FEFF8.4 code. Thus the agglomeration of Cu and Mg, which is accompanied by lattice distortions around Cu atoms, can be probed. A minimal size of Cu–Mg co-clusters is proposed for later stages of natural ageing.

Strength Prediction Method for Unidirectional GFRP after Hydrothermal Aging

This paper proposes a strength prediction method for unidirectional glass fiber reinforced plastics (GFRPs) after hydrothermal aging: immersion in deionized water at 80°C. First, the strength degradation of the constituents (i.e., the glass fiber and the fiber/matrix interface) of unidirectional GFRP after hydrothermal aging was evaluated from the fiber strength and the interfacial shear stress by using a single-fiber composite (SFC). Both the fiber strength and the interfacial shear stress had a tendency to decrease in the early stage of hydrothermal aging and to saturate toward certain values with long-term aging. In addition, the tensile strength of the unidirectional GFRP was measured after hydrothermal aging. The residual strength of the unidirectional GFRP also had a tendency to decrease sharply in the early stage of hydrothermal aging and to saturate toward a certain strength with long-term aging. Finally, the residual strength of the unidirectional GFRP after hydrothermal aging was predicted using the global loading sharing (GLS) model, by considering the degradation of both the glass fiber and the fiber/matrix interface. The predicted results indicated good agreement with the experimental data while considering not only the degradation of the fiber reinforcement but also the fiber/matrix interface adhesion. It was concluded that the GLS model applied considering the degradation of the GFRP constituents would be a suitable and a simple model to predict the residual strength of the unidirectional GFRP after hydrothermal aging.

Effect of temperature and moisture on the luminescence properties of silicone filled with YAG phosphor

In order to determine the environmental effects on the luminescence properties of a phosphor layer for high-power light emitting diodes, a high humidity and temperature test (85 °C/85%RH) and a thermal aging test (85 °C) were performed on silicone/YAG phosphor composites. The luminescence properties of silicone/phosphor composites are monitored by a fluorescence spectrometer. The results show that high temperature could result in an increase in conversion efficiency of composites during the early aging stage and red shift of YAG phosphor; and high humidity could result in a significant decrease in conversion efficiency of composites while having a small influence upon the optimal excitation wavelength of the YAG phosphor.

Elucidating the LiFePO4 air aging mechanism to predict its electrochemical performance

Although LiFePO4-based chemistry has been extensively studied and developed in the last decade due to its promise for the next generation of Li-ion battery applications, the impact of ambient air exposure and the concomitant aging mechanism is still a controversial matter. In the present study, we describe quantitatively the aging process in terms of the successive phase formation, distribution and iron local environments. Formation and growth of a disordered ferric phosphate phase are directly observed for the first time from the surface of particles toward the core, preceding the crystallization of tavorite LiFePO4(OH) as observed through the combination of amorphous phase quantification by XRD, and by Mossbauer and Electron Energy Loss spectroscopies. Structural and electrochemical characterization prove that the amorphous ferric phosphate formed in the early aging stage exhibits already tavorite composition and structure at the local scale and shed light on a crucial step of the aging mechanism. Based on the correlation we establish here between the amounts of Fe(III) and hydroxyls groups present in aged samples and specific capacity of the corresponding electrodes, we show that the degradation of active material upon storage and the electrochemical performance can be predicted easily through simple TGA measurements.