Initial Stage Of Aging Research Articles

High strength, high conductivity and excellent softening resistance Cu-Ni-Fe-P alloy

This article provided a detailed study on the evolution of microstructure and properties of Cu-Ni-Fe-P alloy during thermal mechanical process. The experimental results showed that the Cu-0.3Ni-0.3Fe-0.16P alloy had an optimal comprehensive properties of tensile strength (672 MPa) and electrical conductivity (69.2 %IACS). Through charactering microstructure by the TEM, the results showed that the ultrafine precipitates were (Ni, Fe)2P. The pre-aging sample had a higher tensile strength and electrical conductivity in the initial stage of the final aging because the pre-aging reduced the concentration of the dissolved Ni, Fe and P solutes in the Cu matrix and increased dislocations density during the subsequent rolling. The precipitation strengthening and dislocation strengthening were two main strengthening contributions to the Cu-Ni-Fe-P alloy. The high temperature softening resistance of Cu-Ni-Fe-P alloy was above 500 °C. And the softening mechanism of Cu-Ni-Fe-P alloy was significantly associated with the coarsen precipitates and the recrystallization during the high-temperature annealing. This work provided a guiding significance for the development of high-strength and high-conductivity Cu alloys.

Prediction of storage lifetime of rubber materials for flexible joint elastomers

To investigate the aging performance and storage lifetime of rubber materials used in flexible joint elastomers for solid rocket engines, a compression permanent deformation was used as the performance evaluation index to conduct aging tests on the elastic specimens of joint rubber materials at different temperatures. The results showed that the compression permanent deformation increased with the aging time and temperature, and the value of compression permanent deformation was greater in the initial stage of aging than in the later stage. Based on the regularity of material aging performance, the storage lifetime of rubber materials at room temperature of 25°C is extrapolated to be approximately 17.35 years through the linear equation of aging kinetics. Given that the aging mechanism remains unchanged, the calculation based on the principle of time-temperature equivalence reveals that as the aging temperature of the rubber material increases, the accelerated aging time to reach the regular storage lifetime becomes faster. Aging for 11.25 days at 140°C is equivalent to storing for this rubber material 15 years at 25°C. This research provides references for the future design, manufacturing, maintenance, and storage reliability of flexible joints.

The Initial Stage of Climatic Aging of Basalt-Reinforced and Glass-Reinforced Plastics in Extremely Cold Climates: Regularities.

Detailed analyses of the reasons for changes in the mechanical parameters of fiberglass exposed to different climatic zones have been made available in the literature; however, such detailed studies of basalt plastic do not yet exist. It is possible to make reasonable conclusions on the climatic resistance of reinforced plastics by monitoring the deformation-strength characteristics in combination with fractographic and DMA analyses of the solar- and shadow-exposed parts of the plastics; additionally, one can conduct analyses of the IR spectrum and the moisture sorbtion kinetics. As a starting point for the climatic aging of polymer composite materials, it is necessary to accept the time of exposure in which the maximum values of the elastic strength properties of polymeric materials are achieved. Based on the results of the DMA analysis, it was found that, unlike basalt-reinforced plastics (where the material is post-cured exclusively at the initial stage of the exposure), in glass-reinforced plastic, a process of destruction occurs. The formation of internal stresses in the material and their growth were determined through observing the duration of climatic exposure. The formation of closed porosity, depending on the duration of exposure, can be assessed using the values of the increase in the average moisture content. A set of experimental studies has established that glass-reinforced plastics are subject to greater destruction under the influence of a very cold climate than the basalt-reinforced plastic.

Microstructural evolution and hardening phenomenon caused by aging of AlSi10Mg alloy by laser powder bed fusion

Microstructures and age-hardening phenomena of directly aged (artificial aged) AlSi10Mg alloys fabricated by laser powder bed fusion (LPBF) were characterized using scanning transmission electron microscopy, atom probe tomography, and Vickers hardness testing. The microstructure derived from overlapping melt pools has a full cellular structure consisting of eutectic Si walls surrounding α-Al cells. In the initial stage of aging, solute clusters with density on the order of 1024/m3 were formed in α-Al cells. By prolonging the aging time further, fine Si particles of about 50 nm in diameter precipitated. Before Si precipitation, the hardness of the aged sample was clearly greater than that of the as-built state. With further aging time, the hardness increased further because of the Si precipitation. Cluster analysis revealed that the number density and the size of clusters increased from as-built state by aging, whereas the types of the solute clusters remained almost unchanged by aging. The results indicate that the nanoscale clusters within the α-Al cells, which increase via aging, produce age-hardening effect.

Thermal characteristic evolution of lithium–ion batteries during the whole lifecycle

This work extensively investigates the thermal characteristic evolution of lithium-ion batteries under different degradation paths, and the evolution mechanism through multi-angle characterization is revealed. Under different degradation paths, the evolution trend of temperature rise rate remains unchanged with respect to depth of discharge during the adiabatic discharge process, albeit to varying degrees of alteration. The temperature rise rate changes significantly with aging during the adiabatic discharge process under low-temperature cycling and high-rate cycling paths. The total heat generation rate, irreversible heat generation rate, and reversible heat generation rate exhibit similar evolution behavior with aging under different degradation paths. The interval range of endothermic process of reversible electrochemical reactions increases and the contribution of irreversible heat to the total heat increases with aging. To further standardize the assessment of different degradation paths on the thermal characteristics, this work introduces the innovative concept of “Ampere-hour temperature rise”. In low-temperature cycling and high-rate cycling paths, the ampere-hour temperature rise increases significantly with aging, particularly accentuated with higher discharge rates. Conversely, in high-temperature cycling and high-temperature storage paths, the ampere-hour temperature rise remains relatively stable during the initial stages of aging, yet undergoes a notable increase in the later stages of aging. The multi-angle characterization reveals distinct thermal evolution behavior under different degradation paths primarily attributed to different behavior changes of severe side reactions, such as lithium plating. The findings provide crucial insights for the safe utilization and management of lithium–ion batteries throughout the whole lifecycle.

Effects of Sn addition on precipitation of a pre-naturally aged Al–Zn–Mg alloy during artificial aging

The effect of Sn addition and pre-natural aging on the artificial aging behavior of Al–Zn–Mg alloy was investigated using both experimental approaches and first principle study. The result shows that Sn retards hardness increase at the initial stage of artificial aging by inhibiting the formation of Guinier-Preston zones (I). Atom probe tomography and density functional theory have revealed that the high binding energy of Mg-Sn disturbs Mg-Zn clustering and delays the formation of Guinier-Preston zones (I). However, the retardation effect of Sn on the artificial aging was found to be suppressed when the pre-natural aging was applied to the Al–Zn–Mg–Sn alloy: hardness at the initial stage increased rapidly compared to the Al–Zn–Mg alloy with pre-natural aging. The reason for the rapid increase of hardness in the Al–Zn–Mg–Sn alloy with pre-natural aging is that Guinier-Preston zones (II) was directly formed from vacancy-rich clusters in the Al–Zn–Mg–Sn alloy in contrast to the Al–Zn–Mg alloy with pre-natural aging. This means Mg-Sn and Zn-rich cluster formed during pre-natural aging can accelerate precipitation kinetic by providing nucleation site for Guinier-Preston zones (II) during artificial aging.

Layer-Resolved Mechanical Degradation of a Ni-Rich Positive Electrode

The effects of electrochemical aging on the mechanical properties of electrodes in lithium-ion batteries are challenging to measure and are largely unknown. Mechanochemical degradation processes occur at different scales within an electrode and understanding the correlation between the degradation of mechanical properties, electrochemical aging, and morphological changes is crucial for mitigating battery performance degradation. This paper explores the evolution of mechanical and electrochemical properties at the layer level in a Ni-rich positive electrode during the initial stages of electrochemical cycling. The investigation involves complementary cross-section analyses aimed at unraveling the connection between observed changes on both macroscopic and microscopic scales. The macroscopic constitutive properties were assessed using a U-shaped bending test method that had been previously developed. The compressive modulus exhibited substantial dependency on both the porous structure and binder properties. It experienced a notable reduction with electrolyte wetting but demonstrated an increase with cycling and aging. During the initial stages of aging, electrochemical impedance spectra revealed increased local resistance near the particle–electrolyte interface. This is likely attributable to factors such as secondary particle grain separation and the redistribution of carbon black. The swelling of particles, compression of the binder phase, and enhanced particle contact were identified as probable factors adding to the elevation of the elastic modulus within the porous layer as a result of cycling.

A new viewpoint on aging degradation of polystyrene: From the perspective of molecular weight

In the photo-oxidative aging experiments, the observed trend of the molecular weight of polystyrene (PS) differs from the expected results. By utilizing techniques such as GPC, XPS, SEM, and UV–Vis, it has been demonstrated that the molecular weight of the PS surface decreases during the initial stages of aging, but remains stable in the later stages. The stability in molecular weight is closely associated with the presence of degradation products on the surface of PS. During the experiment, the low molecular weight PS short chains dissolve in the droplets produced by the aging machine, resulting in a reduction of low molecular weight PS chains on the surface. This phenomenon contributes to the maintenance of a stable molecular weight in the later stages. Additionally, this paper introduces a novel method for describing the degree of PS aging, which offers a more intuitive understanding of the degradation process. This method focuses on the number of special patterns obtained through etching away the degradation products, having reference value.

Nucleation and evolution mechanism of precipitates during the initial aging stage in Al-Zn-Mg-Cu alloy

The evolution process and nucleation mechanism of the precipitates during the initial aging stage in Al-Zn-Mg-Cu alloy were studied using the combination of the Cs-corrected high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and first-principles calculations. A new nucleation mode of η' phase with the thickness of 7 at. layers was found, which is parallel to {111}Al planes and consists of 5-layer transition structures and 2 transition layers at the interface. The precipitate is the initial aged η' phase with the simplest structure. Its interfaces are coherent with the Al matrix and meet the stacking periodicity, which is more stable than ordinary η' phases. Besides, the interfaces have a tendency to segregate heavy elements. The presence of segregating atoms enhances the interface interaction and makes it more stable. These two aspects improve the stability of the nano-scale 7-layer particle and maintain the aging strengthening effect of Al alloy.

Lipidomics and volatilomics reveal the changes in lipids and their volatile oxidative degradation products of brown rice during accelerated aging.

Brown rice exhibits higher nutritional value and attracts more and more attentions; however, lipid alteration in brown rice during aging is poorly understood. In this study, lipidomics and volatilomics were employed to investigate free fatty acids, triglycerides, and volatile oxidative degradation products of lipids in brown rice during accelerated aging for 70days. The results showed that the total free fatty acids in brown rice increased significantly (2.90-4.14 times) while triglycerides decreased remarkably at the initial stage of aging. Monounsaturated and polyunsaturated aldehydes, ketones, and acids increased obviously in brown rice during accelerated aging for 70days. The screening of significantly different compounds indicated that the enzymatic hydrolysis of triglycerides (EHT) and enzymatic oxidation of lipids (EOL) were the main biochemical behaviors at the initial stage of aging (0-28day) while automatic oxidation of lipids (AOL) was the primary chemical reaction for 28-70days aging.

Improved Cu/Sn interface reliability using double-layer stacked nano-twinned Cu

The immoderate growth of intermetallic compound (IMC) at the Cu/Sn bonding interface reduces the reliability of bonding joints, leading to the failure of high-density packaging. Herein, we design a double-layer nanotwinned Cu (d-ntCu) structure composed of the perpendicularly aligned nano-twinned Cu (p-ntCu) as the upper layer and horizontally aligned nano-twinned Cu (h-ntCu) as the lower layer. We study the Cu/Sn bonding interface microstructure evolution to reveal the IMC growth inhibition and void suppression ability of d-ntCu. As a comparison, the interface microstructure evolution of single layer h-ntCu/Sn is also studied. After thermal aging, the growth mode of IMC at the Cu/Sn bonding interface can be divided into two stages, which are caused by the in-situ annealing of the p-ntCu. In the initial stage of aging, the main diffusion path of Cu atoms is twin boundary diffusion, causing a rather fast growth of IMC. After 100 h aging, the twins anneal into large grains, which induce a lower growth rate of IMC due to the bulk diffusion of Cu atoms. Compared with the h-ntCu single layer, the IMC thickness of the d-ntCu is suppressed by 20%. Besides, the bonding interface in d-ntCu/Sn is void-free due to the vacancy-sink effect of twin boundaries. Therefore, using d-ntCu as the substrate can not only control the IMC growth rate but also suppress the formation of voids during aging, which is helpful to achieve high bonding reliability.

Age-hardening Behavior in <i>γ</i>′-phase Precipitation-hardening Ni-based Superalloy

Dislocations are often introduced in Ni-based superalloys to impart sufficient strength at both room temperature and high temperatures prior to their use in automobile exhaust gaskets. However, the interaction between the representative γ′ (Ni3(Al, Ti))-phase precipitates and dislocations in high temperature remains unclear. Therefore, this study examined the effect of cold rolling on age-hardening behavior and microstructure evolution, focusing on the formation of γ′-phase Ni3Ti during aging at 700°C for up to 400 h after 60% cold rolling of solution-treated specimens. During the early stage of aging, at 0.03 h, the hardness rapidly increased from 401 HV to 496 HV. Age-hardening continued until 3 h and reached its peak of 536 HV, followed by gradual decrease with aging time. 3D atom probe investigation revealed that the γ′-phase was confirmed after 0.3 h of aging. However, the composition-modulated structure speculated to be caused by spinodal decomposition was observed in the 0.03 h aged specimen. The change in strength with aging time was considered by calculating the contribution of each strengthening mechanism. In the initial stage of aging (0–3 h), dislocation and solid-solution strengthening dominated along with spinodal strengthening. Strengthening by spinodal decomposition in the 0.03 h aged specimen is presumptively accelerated by the introduced dislocations, which is followed by further precipitation strengthening caused by γ′-phase precipitates. In the later stage of aging (3–400 h), precipitation strengthening became dominant and reached its peak at 20 h aging, while dislocation strengthening decreased with aging time.

Clustering evolution during low temperature aging and thermal stability during two-step aging in Al-Mg-Si alloys

The age-hardening response during two-step aging in Al-Mg-Si alloys depends on the nanoclusters formed at the early stage of phase decomposition. However, understanding of the evolution and thermal stability of the nanoclusters is still lacking. This paper discusses clustering behavior during natural aging (NA) and pre-aging (PA) at 50 ℃ through various experiments [hardness, differential scanning calorimetry (DSC), electrical resistivity and three-dimensional atom probe (3DAP)]. A rapid increase in hardness is confirmed due to the acceleration of cluster formation during PA, and a larger area of an endothermic peak is confirmed during DSC thermal analysis compared to NA specimens. Hardness and electrical resistivity were clearly decreased in the PA specimens at the initial stage of two-step aging since the formation of thermally unstable clusters, the Mg-enriched clusters identified by 3DAP, was accelerated during PA. A long aging time at 50 ℃ produces Mg-enriched clusters rather than facilitating the transition from Cluster (1) to Cluster (2). To investigate the atomic arrangement of a cluster, we conducted further analysis for chemical composition of clusters through the normalization for the different sizes of cluster. We found that the Mg-rich clusters with the core-shell structure where Mg atoms are segregated around the cluster-matrix interface, cause thermally unstable at the initial stage of two-step aging. The direct experimental evidence primarily proves that atomic arrangement inside a cluster is a more critical factor than its size for the thermal stability of a cluster in Al-Mg-Si alloys.

Co-strengthening of the multi-phase precipitation in high-strength and toughness cast Al–Cu–Zn–Mg alloy via changing Zn/Mg ratios

The effects of the Zn/Mg ratio on the as-cast microstructure, aging-precipitation behavior, and mechanical properties of cast Al–Cu–Zn–Mg alloys, an interesting precipitation-hardened Al alloy different from the 2XXX and 7XXX, were investigated. The primary phase of the as-cast alloy changed from lamellar θ and S phases to a block S phase with an increased Zn/Mg ratio. The number density of the solely S phases in the peak-aged alloy increased with the Zn/Mg ratio from 0.4 to 1.5, because the Zn promoted the formation of GPB zones. At a Zn/Mg ratio of 2.5, the major precipitates are the S, η, and T phases, due to the preferential interaction of Mg atoms with Zn, which promotes the formation of Mg–Zn clusters and GP zones in the initial stages of aging. The yield strength, ultimate tensile strength, and elongation reached maximum values of 372 MPa, 502 MPa, and 12.3%, respectively. This illustrates the cooperative strengthening of the S, T, and η phases, which pin the moving dislocations and inhibit crack initiation and propagation. A large amount of the T phase in the high Mg content alloy suppresses the formation of the S phase. This multi-phase precipitation addressed the “strength ductility trade-off” in cast Al alloys.

Effects of Cu Addition on Age Hardening Behavior and Mechanical Properties of High-Strength Al-1.2Mg-1.2Si Alloy.

In this study, the effects of Cu addition on artificial age hardening behavior and mechanical properties of Al-1.2Mg-1.2Si-(xCu) alloy was investigated quantitatively and qualitatively by Vickers hardness, tensile test, and transmission electron microscope. The results indicated that Cu addition enhanced the aging response of the alloy at 175 °C. With the increase in Cu content, the time for the alloys to reach peak aging decreased from 12 h to 10 h and 8 h. The tensile strength of the alloy was obviously improved with Cu added in which was 421 MPa of 0Cu alloy, 448 MPa of 0.18Cu alloy, and 459 MPa of 0.37Cu alloy. The results of TEM observation revealed that the addition of 0.37Cu changed the aging precipitation sequence of the alloy, in which the precipitation sequence of 0Cu and 0.18Cu alloy was SSSS→GP zones/pre-β″→β″→β″ + β', 0.37Cu alloy was SSSS→GP zones/pre-β″→β″ + L→β″ + L + Q'. Moreover, with the addition of Cu, the number density and volume fraction of precipitates of the Al-1.2Mg-1.2Si-(xCu) alloy was evidently increased. The number density was increased from 0.23 × 1023/m3 to 0.73 × 1023/m3 in the initial aging stage and from 1.9 × 1023/m3 to 5.5 × 1023/m3 in the peak aging stage. The volume fraction was increased from 0.27% to 0.59% in the early aging stage and from 4.05% to 5.36% in the peak aging stage. It indicated that Cu addition promoted the precipitation of strengthening precipitates and boosted the mechanical properties of the alloy accordingly.

Strain ageing embrittlement behaviour of X80 self-shielded flux-cored girth weld metal

ABSTRACT Strain ageing embrittlement behaviour of X80 self-shielded flux-cored arc welding (FCAW) girth weld metal at different strain ageing conditions (1% prestrain, and aged at 150°C/100°C for 1 –6 h, and 80°C for 1–30 days) was studied. Microstructure of FCAW girth weld generally consisted of coarse granular bainite and lath bainite. After strain ageing, toughness notably decreased, and higher ageing temperature or longer ageing induced lower toughness, until ageing is fully yielded. At initial stage of strain ageing, more dimples were found accompanying with cleavage facet. With the progress of strain ageing, the embrittlement was more obvious, while larger cleavage facet and less dimples were found. Meanwhile, the critical size for cleavage fracture initiation site became smaller. Martensite–austenite constituent (1–2 μm) was found to initiate cleavage fracture when partially strain aged, while submicron inclusions could initiate cleavage facet when fully strain aged.

Effect of secondary aging on microstructure and properties of cast Al-Cu-Mg alloy

To obtain better comprehensive properties of cast Al-Cu-Mg alloys, the secondary aging (T6I6) process (including initial aging, interrupted aging and re-aging stages) was optimized by an orthogonal method. The microstructures of the optimized Al-Cu-Mg alloy were observed by means of scanning electron microscopy and transmission electron microscopy, and the properties were investigated by hardness measurements, tensile tests, exfoliation corrosion tests, and intergranular corrosion tests. Results show that the S phase and θ′ phase simultaneously exist in the T6I6 treated alloy. Appropriately increasing the temperature of the interrupted aging in the T6I6 process can improve the mechanical properties and corrosion resistance of Al-Cu-Mg alloy. The optimal comprehensive properties (tensile strength of 443.6 MPa, hardness of 161.6 HV) of the alloy are obtained by initial aging at 180 °C for 2 h, interrupted aging at 90 °C for 30 min, and re-aging at 170 °C for 4 h.

Discontinuous precipitation in a Cu-10Ni-1Si alloy with ultra-high strength, high shock absorption, and good stress relaxation resistance

The discontinuous precipitation in a Cu-10Ni-1Si alloy aged at 500 °C and 550 °C was studied to clarify the types of discontinuous precipitates, and the crystal relationships between precipitates and the matrix. The continuous δ-Ni2Si precipitates were detected in the initial aging stage, then discontinuous β-Ni3Si and continuous δ-Ni2Si precipitates were detected simultaneously. The crystal relationship between discontinuous β-Ni3Si precipitates and the copper matrix at the beginning of aging was that: (1̅11̅)Cu//(111̅)β, [011]Cu//[011]β. The lamellar discontinuous β-Ni3Si precipitates significantly improve stress relaxation resistance and damping properties, which are attributed to the interaction between lamellar structure and dislocation motion. These findings indicated that the formation of the lamellar discontinuous precipitates tends to prevent dislocation slip and promote precipitation, resulting in enhanced mechanical properties and conductivity properties simultaneously.

The Role of PEDF in Reproductive Aging of the Ovary.

Reproductive aging is characterized by a decline in ovarian function and in oocytes’ quantity and quality. Pigment epithelium-derived factor (PEDF), a pivotal player in ovarian angiogenic and oxidative balance, was evaluated for its involvement in reproductive aging. Our work examines the initial stage of reproductive aging in women and mice, and the involvement of PEDF in the process. Granulosa cells from reproductively-aged (RA) women and mice (36–44 years old and 9–10 months old, respectively) indicated an increase in the level of PEDF mRNA (qPCR), with yet unchanged levels of AMH and FSHR mRNAs. However, the PEDF protein level in individual women showed an intra-cellular decrease (ELISA), along with a decrease in the corresponding follicular fluid, which reflects the secreted fraction of the protein. The in vitro maturation (IVM) rate in the oocytes of RA mice was lower compared with the oocytes of young mice, demonstrated by a reduced polar body extrusion (PBE) rate. The supplementation of PEDF improved the hampered PBE rate, manifested by a higher number of energetically-competent oocytes (ATP concentration and mtDNA copy number of individual oocytes). Our findings propose PEDF as an early marker of reproductive aging, and a possible therapeutic in vitro agent that could enhance the number of good-quality oocytes in older IVF patients.

Revealing trace Si effect on precipitation behavior and properties of Cu-Cr-Zr alloy: Experiments and first-principles calculations

High-performance Cu-Cr-Zr-X alloys are regarded as novel structural materials for nuclear fusion reactors. Through combining the experiments and density functional theory (DFT), the effect of Si addition on precipitation behavior and related properties of Cu-Cr-Zr-(Si) alloy was investigated for higher performance. Compared with the Si-free alloy, precipitation of Cr-rich phase is accelerated in the Cu-Cr-Zr-Si alloy (aging time<30 min at 450 °C). The partial radial distribution functions of the Cu-rich matrix reveal that the formation of Si-Cr clusters is resulted from the attractive Si-Cr binding energies at the nearest-neighbor distance. Moreover, the addition of Si can reduce the Cr migration energy in Cu. At the initial stage of aging at 550 °C, the precipitation kinetics is dominated by temperature. By TEM analysis, it is indicated that the growth of Cr-rich phase in Cu-Cr-Zr-Si alloy is delayed, which may be attributed to the decrease of Cu/Cr interface energy due to the addition of Si, as confirmed by first-principles calculations. The optimized performance of aged Cu-Cr-Zr-Si alloy can be achieved at 450 °C/4 h, and Orowan strengthening is dominant. This work can provide a guideline for design of novel high-performance Cu-Cr-Zr-X alloys.