Room Temperature Aging Research Articles

Fabrication of boehmite nanofiber aerogels by a phosphate gelation process for optical applications

A transparent wet gel was obtained in a few minutes at room temperature by adding an aqueous phosphoric acid solution of appropriate concentration to boehmite nanofiber sol. After room temperature aging and supercritical carbon dioxide drying, low bulk density aerogels with visible light transmittance of over 90% at 10 mm thickness were obtained. These aerogels exhibited high Young’s modulus and visible light transmittance, while having the same bulk density as the samples obtained by a conventional gelation process using a base. The high optical transmittance of the aerogel were hardly lost even at high humidity because the phosphorylation of the skeletal surface reduced the percentage of hydroxyl groups. The three-dimensional imaging inspection of the exterior and interior of the aerogel was carried out. The various developments reported in this paper make aerogels with ultralow bulk density (<0.01 g cm−3) and high visible light transmission even more promising for applications in the physical field. Graphical abstract

Change in elastic properties during room-temperature aging in body-centered cubic Mg–Li and Mg–Li–Al single crystals

• A complete set of elastic constants of Mg-40Li and Mg-40Li-5Al (at.%) single crystals, developed for biodegradable orthopedic implants, were measured. • The Young's moduli of the Mg-Li and Mg-Li-Al single crystals strongly depend on the crystallographic direction. • The Young's modulus along the 〈100〉 direction is approximately 21 GPa, which perfectly match with that of natural bones. • The Young's moduli along 〈100〉 in the Mg-40Li and Mg-40Li-5Al alloys changed during aging near room temperature, which was revealed for the first time. The elastic properties and room-temperature aging behaviors of body-centered cubic Mg–40Li and Mg–40Li–5Al (at.%) alloy single crystals, developed for biodegradable orthopedic implants, were investigated by measuring their single-crystalline elastic constants. It was found that the Young's moduli of Mg–40Li and Mg–40Li–5Al single crystals strongly depend on the crystallographic direction, and the Young's modulus along the 〈100〉 direction is approximately 21 GPa, which is almost the same as that of natural bones. More importantly, we found that the Young's moduli along < 100 > in the Mg–40Li and Mg–40Li–5Al alloys changed during aging near room temperature, which may have been caused by the precipitation or dissolution of the θ -phase MgAlLi 2 or hcp α-phase.

Indentation characterization of glass/epoxy and carbon/epoxy composite samples aged in artificial salt water at elevated temperature

Micro-level composite properties are a key determinant of the long-term performance and life span of marine-based composite structures. In this paper, the effect of the aging process in salt water at room temperature and elevated temperature on the elastic modulus and hardness of composite specimens have been investigated through indentation testing. To do this, carbon/epoxy (CE) and glass/epoxy (GE) samples were immersed in artificial sea water with 3.5% salinity at room temperature and 60 °C for 90 days. Matrix only and fibre/matrix (fibre constraint) cells have been examined by two different approaches, namely standard indentation testing and continuous stiffness measurement (CSM) methods to measure elastic modulus and hardness in micro level. It was indicated that degradation at 60 °C had a higher effect on elastic modulus than the room temperature aging process. According to the experimental results from the standard method indentation in matrix cells, the average modulus in the aged GE in 60 °C was 3.47 ± 0.1 GPa (22.3% loss). The average modulus in the reference CE samples was 4.7 ± 0.1 GPa, while those values for aged samples at room temperature and 60 °C showed 38.8% and 51.3% losses, respectively. The hardness for the reference GE specimen was 0.189 ± 0.004 GPa, and after the aging process, it dropped by 2.1% (room temperature) and 27.51% (60 °C). Based on the continuous stiffness measurement for matrix cells, the mean value of modulus for the dry GE and CE matrix material cells was calculated as 4 GPa and 3.7 GPa, respectively. During the aging process, the hardness of CE samples decreased from 0.048 GPa to 0.038 GPa at room temperature and 60 °C, respectively, while aging of GE samples at both temperatures after 90 days caused a 31% loss in the hardness compared to the reference specimen. It was evident from the CSM experiments in the fibre constraint cells that the indentation modulus of the dry epoxy matrix constituent increased by 7.5% and 14% by the neighbouring stiff glass and carbon fibre regions respectively. The indentation characterization in GE samples thorough the standard method in the fibre constraint cells showed a 12.58% reduction in modulus at room temperature, and 25.8% at 60 °C compared to the reference specimen.

Electrodeposited Ni-W coatings as the effective reaction barrier at Ga-21.5In-10Sn/Cu interfaces

In this study, the long-term (up to 400 days) room temperature aging tests for Ga-21.5In-10Sn/Cu interface were investigated, confirming the formation of intermetallic compounds at room temperature could cause the serious interfacial instability issues. One novel strategy using solid solution alloys with high thermal stability and high diffusion activation energy to design the barrier layer materials to inhibit the diffusion of solid atoms or interfacial reactions was proposed. The feasibility of Ni-W and Ni-W-graphene coatings as the interfacial reaction barrier of Ga-21.5In-10Sn/Cu liquid-solid interfaces was explored, indicating a novel application of Ni-W electroplated coatings in electronic/electrical contacts fields besides these traditional applications in wear-resistance, corrosion-resistance and heat corrosion resistance fields. The challenging agglomeration issues of graphene in water soluble solutions was successfully solved using the ethylene glycol as the effective dispersant. The temperature dependence of Ni-W and Ni-W-graphene coatings as the interfacial reaction barrier was compared. It was preliminarily contended that the addition of graphene particles was detrimental to improve the reaction barrier properties of Ni-W matrix. This finding provides a novel strategy to solve the interfacial instability problem of Ga-21.5In-10Sn/Cu interfaces and will enable wider applications of electroplated Ni-W coatings, promoting the development of soft and stretchable Ga-based alloys/Cu conductors in wearable electronics.

Effect of ECAP processing on distribution of second phase particles, hardness and electrical conductivity of Cu−0.81Cr−0.07Zr alloy

The effect of equal-channel angular pressing (ECAP) processing at room temperature and 300 °C on the distribution of the second phase particles and its influence on hardness and electrical conductivity of the commercial Cu−0.81Cr−0.07Zr alloy were investigated. Microstructural characterization indicated that the area fraction of coarse Cr-rich particles decreased after ECAP processing. This reduction was attributed to the Cr dissolution induced by plastic deformation. The electrical conductivity of the alloy decreased by 12% after 4 ECAP passes at room temperature due to the increase of electrons scattering caused by higher Cr content in solid solution and higher density of defects in the matrix. These results were supported by the reduction of the Cu lattice parameter and by the exothermic reactions, during differential scanning calorimetry (DSC) analysis, observed only in the samples subjected to ECAP processing. Aging heat treatment after ECAP processing promoted an additional hardening effect and the complete recuperation of the electrical conductivity, caused by the re-precipitation of the partially dissolved particles. The better combination of hardness (191 HV) and electrical conductivity (83.5%(IACS)) was obtained after 4 ECAP passes at room temperature and subsequent aging at 380 °C for 1 h.

Identifying the true structure and origin of the water-quench induced hydride phase in Zr-2.5Nb alloy

The crystal structure of the hydride induced by water quenching in hydrided Zr-2.5Nb pressure tube was identified by a combined approach of synchrotron x-ray diffraction and TEM nano-beam electron diffraction, coupled with density functional theory. It has been found that the hydrides experimentally characterized have the same face-centered tetragonal lattice structure as that of the γ-phase, however the hydrogen atoms did not show evidence of ordering. The quenched hydrides subsequently transformed into both ordered face-centered tetragonal (i.e., γ-phase) as well as δ-phase during a one-year room temperature aging, implying a metastable nature; therefore, we argue it is appropriate to identify these initial quenched hydrides as γ′ instead of the γ hydride the majority of literature has used in the past. The amount of γ′ phase is found to increase with the temperature at which the sample is quenched from, while the amount of δ phase changed inversely. In-situ heating experiments with synchrotron diffraction on samples with various prior heat treatments were also conducted; the γ′ phase was found to be present at temperatures up to 278˚C. Transformation of γ′ into δ hydride was found to occur upon heating, confirming the relative stability of the two phases. The origin of the γ′ phase is compatible with the newly confirmed Zr-H phase diagram where γ-hydride exists as the low temperature stable phase.

Formation and time dynamics of hydrogen-induced vacancies in nickel

The formation of hydrogen-induced defects in nickel was investigated by positron annihilation lifetime spectroscopy (PALS) and the time dynamics of those defects during room temperature aging was tracked with an unprecedented time resolution of the order of minutes using an ultrahigh-flux slow positron beam. Those measurements showed the formation of a large number of atomic vacancies simply by hydrogen addition at room temperature. Low-temperature PALS measurements indicated that they were monovacancy-level defects and low-temperature coincidence Doppler broadening measurements proved that hydrogen was trapped and bound to those vacancies during the hydrogen charge. Room temperature aging, i.e. below the stage III temperature in Ni, and the concomitant hydrogen desorption induced the agglomeration of those monovacancies into large vacancy clusters which remained even after all the hydrogen had desorbed and hydrides had disappeared. These results constitute the first empirical evidence that vacancy-hydrogen complexes are induced in Ni only by hydrogen charging and demonstrate that hydrogen has a primary role in the formation and stabilization of vacancies even at room temperature.

Broadband visible to mid-infrared aluminum-black absorbers and the aging behavior

Broadband light absorbers are attractive for their applications in solar-energy harvesting, thermal detectors and photodetection. Metal-black absorbers have been experimentally proved having broadband light absorption and low mass density. Expensive gold and silver metal-black absorbers have shown excellent performances in various applications. Here, we present low-cost aluminum (Al) -black absorbers fabricated by thermal evaporation processes. The average absorption of Al-black coatings with evaporation time of 10, 20 and 30 s were 60.82%, 84.83% and 92.18% in 320–2500 nm spectral range and 92.82% (30 s) in 2.5–15 μm, demonstrating that Al-black films can be used as low-cost broadband light absorbers. Long-term stability of optical properties was a significant technological concern for metal-black absorbers. Therefore, room temperature aging behaviors of Al-black absorbers were investigated. Comparative analyses on morphological, atomic content, spectral absorption and photothermal response before and after 60 days and 120 days of room temperature aging of the Al-black absorbers were carried out. The aging of the Al-black films was attribute to the mechanical pressure and oxidation. The aged Al-black absorber exhibited similar absorption and time-dependent photothermal response characteristics as that before aging from visible to mid-infrared spectral range. These results indicated that the Al-black films possessed excellent stability of solar absorption and photothermal response after aging, which can be low-cost alternative absorbers of expensive metal-black films.

Effect of Sc on solidification segregation and subsequent friction stir processing of aluminium alloy

Al-Zn-Mg alloys (7xxx series) are used in aerospace engineering due to their high strength-to-weight ratio and good mechanical properties. Al-Zn-Mg alloy is exhibited strong age-hardening properties due to the Sc (0.39 wt%) inoculation effects, which implies decomposition of the supersaturated solid solution and the formation of a fine distribution of coherent GP-zones precipitates, ή precipitates, η(stable) and Al3Sc(L12) precipitates. In addition, the ageing sequence consists of mainly three steps such as solutionizing at 465 °C for 1 h then immediately water quenching (T4), subsequently, room temperature ageing, and again proceed artificial ageing at 140 °C for 6 h (T6). The microstructure at peak strength is shown to depend on the mainly dissolution of GP zones, nucleation of ή and Al3Sc precipitates or formation of GP zones, nucleation of dislocations and dislocation with Al3Sc particles interaction. Thus, at higher temperature around 140 °C the ή transition phase is being formed and thermal stability of Al3Sc phase at > 300 °C. It has also identified those ageing treatments both operation eliminated micro-segregations and improved mechanical properties of this alloy. The influence of various process parameters on the microstructure and mechanical properties of the as-cast alloy and FSP of aluminium alloy are studied by OM, EPMA, FESEM, DSC, TEM, Vicker’s hardness measurements and tensile properties. The combined effect of Sc addition, FSP then later on post ageing treatment at 140 °C for 2 h significantly enhanced better tensile properties (278.8 MPa, ductility 6.7%) when compared to the T6 ageing treatment with Sc addition (340 MPa, ductility 4.8%). The aim of this paper is to investigate in details the ageing behaviour at T6 condition, and examine microstructural effect after optimized FSP parameters at 1000 rpm, traverse speed of 70 mm/min, specified tool design and induced heat input (1.07 kJ/mm) on Al-Zn-Mg-Sc alloy to enhances mechanical properties after post ageing treatment at 140 °C for 2 h.

Contribution of structural parameters to the strength and electrical conductivity of Cu-0.5%Cr alloy subjected to ECAP and cold rolling

The effect of cold rolling with a reduction rate of 95% at room temperature and subsequent aging on the evolution of the microstructure, strength properties and electrical conductivity of the Cu-0.5Cr alloy (wt.%), which is widely used in the electrical industry in the form of strips and ribbons, has been studied. The cold rolling and aging of the alloy was carried out in coarse-grained and ultrafine-grained states after equal-channel angular pressing. The regularities found were used to assess the contribution of various structural parameters to the level of strength properties as well as the electrical conductivity of the alloy in the obtained states.

Effect of two-step cryorolling and aging on mechanical and electrical properties of a Cu–Cr–Ni–Si alloy for lead frames applications

Abstract High strength and high electrical conductivity Cu–Cr-based alloys are important candidate materials for preparing lead frames, railway contact wires and connects. However, high strength and high electrical conductivity are mutually exclusive in nature. To optimize the mechanical and electrical properties of a Cu–Cr–Ni–Si alloy, the two-step cryorolling and aging (CRA) was carried out in this study. Here, by the analysis of microstructure evolution, precipitation behavior, and corresponding strengthening mechanisms of the alloy at different rolling and aging conditions, we find that the yield strength and electrical conductivity for the two-step CRA sample are improved by 91.3 MPa and 4.9 %IACS (International Annealed Copper Standard) than those of the sample subjected to single-step room temperature rolling and aging (RTRA). The higher yield strength for the two-step CRA sample is mainly determined by the precipitation strengthening contributed from Ni2Si and Cr precipitates, rather than the twin boundary strengthening and dislocation strengthening. In fact, the dislocation density of the two-step CRA sample is lower than that of the single-step RTRA sample because of the faster drop rate of recovery, which weakens the effect of dislocation strengthening. The combination of the first-step aging and second-step CR process for the two-step CRA sample contributes to the formation of more precipitates from the matrix, thereby significantly increasing the precipitation strengthening and decreasing the impurity scattering in the final aging. The results provide a new preparation process and a reliable theoretical approach for optimizing the mechanical and electrical properties of the Cu–Cr alloys.

The Structure of Annealed Hafnium Bronze Subjected to Severe Plastic Deformation by High Pressure Torsion

The structure and mechanical properties of low-alloyed hafnium bronze (Cu-0.78 wt. % Hf) under severe plastic deformation by high-pressure torsion (HPT) by 1, 3 and 5 revolutions of anvils at room temperature have been studied by electron microscopy and microhardness measurements. In the initial annealed state Hf is practically completely bonded in intermetallic compounds. The structure of bronze specimens deformed by HPT is stable and does not undergo any changes after unloading and long room temperature ageing. Under the deformation a dispersed submicrocrystalline structure gradient along specimen radius is formed. Average crystallite size in the radius middle is 200 nm after 1 revolution and 120 nm after 5 revolutions of anvils. It is demonstrated that in all the specimens studied including those deformed by 5 revolutions the structure is not uniform which is confirmed by microhardness measurements. Such behavior of hafnium bronze with Hf bonded in precipitates has much in common with the behavior of pure copper. However, the room temperature stability of the structures obtained by HPT demonstrates similar behavior with that of low-alloyed tin bronze.

Towards resolving a long existing phase stability controversy in the Zr-H, Ti-H systems

In the binary Zr-H, Ti-H systems, there are three common hydride phases, namely γ-, δ-, and ε-hydride, with different ratios of H to Zr/Ti atoms. Among them, the relative stability of γ-hydride remains controversial, although it has been observed in many studies. In this study, we demonstrate that γ-hydride is the only stable hydride phase in high purity Zr and commercial purity Ti, using electrolytically loaded hydrogen and ex-situ synchrotron x-ray diffraction. Further, in-situ synchrotron heating/cooling experiments were conducted with hydrided pure Zr sample demonstrating the co-existence of γ- and δ-hydride phase, from a furnace cooling heat treatment followed by three days room temperature aging. It is shown that during heating γ-hydride dissolved first, while δ-hydride remained stable at temperatures up to 280°C, followed by dissolution of δ-hydride until all hydrogen was in solution. Under subsequent slow cooling, δ-hydride precipitated first, followed by a slow formation of γ-hydride when temperatures were below 210°C, which continued during a subsequent 60 hours aging at room temperature. The phase stability when hydride forms as precipitates in Zr is therefore determined to be δ-hydride as the high temperature phase, and γ-hydride as the low temperature phase. The microstructural characteristics of γ-hydride in Zr and Ti were studied by electron microscopy. The observed co-existence of γ- and δ-hydride as well as change from δ to γ during long term room temperature aging in the TEM confirmed the synchrotron data.

New insights into fracture of Si in Cu-filled through silicon via during and after thermal annealing

Copper (Cu)-filled through silicon (Si) via (CF-TSV) acts as an electrical conduit between different layers of circuitry in the advanced microelectronic devices. Due to wide difference in the coefficient of thermal expansion between Cu and Si, large thermal stresses get generated in both Si and Cu during the inevitable thermal excursions taking place during fabrication of microelectronic devices and their regular operation. This study examines the fracture of Si wafer in a CF-TSV due to annealing over the temperature range of 250–550 °C and the post-annealing natural ageing. Nucleation of micro-cracks in Si in the vicinity of the Cu pillars were observed, which propagated at a constant velocity during post-annealing room temperature ageing, thereby substantiating delayed fracture in Si. Microstructural examination revealed that the micro-cracks nucleated as a result of formation of a Cu-Si compound during annealing, whereas the crack propagated due to the oxidation of Si at the crack tip. Consistently, the micro-cracks did not propagate when the sample was stored in high vacuum. Furthermore, Raman spectroscopy and finite element method were used to gain insights into stress generation due to Cu-Si reaction, and nucleation and propagation of the crack.

Aging stability of bio-oil produced from dewatered sewage sludge in subcritical water

In this study, the stability of bio-oil produced from the hydrothermal liquefaction of dewatered sewage sludge was examined under room-temperature and accelerated-aging conditions at 80 °C over 6 months. No significant change was observed in the fluidity, viscosity, or molecular weight of the room-temperature bio-oil samples. The accelerated-aged bio-oil samples maintained their fluidity for up to 1 week, and substantial increases in the viscosity and molecular weight were observed in the samples aged for more than 1 month. Additionally, the decomposition behaviors of the room-temperature-aged samples were considerably similar to that of fresh bio-oil, whereas the low-temperature decomposition peak at 86 °C progressively decreased and shifted toward the high-temperature direction with increasing accelerated-aging time. The composition analyses of the aged bio-oil samples indicated that low-molecular-weight species, such as ethylbenzene, 1H-indole, 3-methyl-1H-Indole, cetene, 3-hexadecene, 1-decene, 2,4,6-trimethyl-benzonitrile, and 2,5-dimethyl-pyrazine, persisted during room-temperature aging, but disappeared as the accelerated-aging period increased.

The Possible Side Reaction in the Annealing Process of Perovskite Layers.

The high purity of light harvesting layers is one of the core issues for highly efficient perovskite solar cells. The perovskite precursor solution and the crystallization growth of thin films have been extensively studied in the past few years. Herein, we have unveiled some side reactions that occur during the evaporation of the residual solvent in the spin-coated films at elevated temperature, forming N-methyl formamidium iodide and N,N'-dimethyl formamidium iodide. Such side reactions will consume the precursor materials and then produce a secondary phase in the perovskite films, which is detrimental for the performance improvement. We have also found that a combination of room temperature aging and vacuum treatment of the spin-coated wet film is conducive to eliminate the side reactions and improve the perovskite phase purity, reaching an efficiency of 20.98%.

Stress-relaxation viewpoint to study the room-temperature cyclic deformation behavior of a low-density steel

A novel method is offered with the task of unveiling the underlying micro-mechanisms of cyclic deformation. This method by merging of dwell-fatigue and stress relaxation concept provides the capability of assessment of the dislocation response to cyclic deformation and subsequently the differences between tensile and compressive half-cycles behavior. Interestingly, the apparent activation volume and mobile dislocation density have been successfully calculated in the course of cyclic loading. Noteworthily, room-temperature dynamic strain aging is firmly proved through these novel findings in a cyclically-loaded lightweight steel. This promises to be a breakthrough in deep understanding the behavior of materials under cyclic loading.

DSC Cycling Effects on Phase Transformation Temperatures of Micron and Submicron Grain Ni50.8Ti49.2 Microwires

The effect of thermal cycling parameters on the phase transformation temperatures of micron and submicron grain size recrystallized Ni–Ti microwires was investigated. The suppression of martensitic transformation by thermal cycling was found to enhance when combined with room temperature aging between the cycles and enhances even more when aged at elevated temperature of 100 °C. While aging at room temperature alone has no clear effect on the martensitic transformation, elevated temperature aging at 100 °C alone suppresses the martensitic transformation. All aforementioned effects were found to be stronger in large grain samples than in small grain samples. Martensitic transformation suppression in all cases was in line with the formation of Ni4Ti3 precursors in the form of 〈111〉B2 Ni clusters as concluded from the observed diffuse intensity in the electron diffraction patterns revealing short-range ordering enhancement. Performing thermal cycling in some different temperature ranges to separate the effect of martensitic transformation and high temperature range of DSC cycling revealed that both high temperature- and martensitic transformation-included cycles enhance the short-range ordering.

Fatigue life prediction of tire sidewall using modified Arrhenius equation

Prolonged exposure of tires to sunlight leads to hardened and cracked sidewall rubber, which significantly decreases the fatigue life of the tire. Aging changes the rubber properties, which affects the safety of the sidewall, reduces the ride comfort, and even causes accidents. Hence, fatigue test procedures and regulations for tire materials are necessary to ensure the safety and reliability of vehicle tires. However, when developing a new tire sidewall, manufacturers typically only test the changes in physical properties of compounds. This study proposes a method of evaluating the fatigue life of aged tire sidewalls. In this process, by applying the Arrhenius equation, each aging condition is converted into its equivalent room temperature aging condition to predict the fatigue life changes with respect to aging. Moreover, a new fatigue parameter is presented to analyze the fatigue behavior of aged rubber and elucidate the cause of fatigue life changes. The probability distribution of fatigue life is expressed using Weibull distribution, and the durability performance is evaluated by comparing the fatigue life of unaged and aged tires.

Long-term room-temperature aging treatment of a bulk metallic glass composite

In this work, a long-term room-temperature aging treatment of the order of years is applied to a B2 phase-reinforced CuZr-based bulk metallic glass composite (BMGC). Presumably governed by residual stress, B19’ CuZr martensitic phase gradually precipitates in the crystals after such long-term aging, while structural relaxation takes place in the glassy matrix, which finally induces precipitation of Cu10Zr7 nanocrystals. Tensile tests prove that these time-dependent structural changes have a measurable effect on deformation behaviors of BMGC. The findings are helpful for understanding the thermodynamic stability and the kinetics of structural evolution of metastable alloys and have useful implications for tailoring the structure and mechanical behavior of BMGCs.