Longer Aging Times Research Articles

Long-time aging in 3 mol.% yttria-stabilized tetragonal zirconia polycrystals at human body temperature

We present new findings on the low-temperature degradation of yttria-stabilized zirconia at 37°C over several years and at high and low partial pressures of water. With the aid of focused ion beam cross-section confirmation studies we are able to show an extensive linear, continuous degradation without retardation, even at low temperatures and low water pressures. The characteristic layer growth and its inferred rate constant imply a lifetime of tens of years under simple tension and open the possibility of studying the longevity of these ceramics more rigorously. In addition, we show reproducibility complications of accelerated aging tests by the use of different autoclaves and possible implications for standardized procedures.

Dynamic fracture analysis of aged glassy polycarbonate by the method of caustics

The purpose of this work is to investigate the dynamic fracture properties of glassy polycarbonate (PC) with different aging times. The optical method of caustics is adopted in which the shadow spot patterns are recorded by a high speed camera during the dynamic fracture process. Then, the dynamic crack propagation, the stress intensity factor (SIF) and the dynamic fracture toughness of aged PC are obtained through an analysis of the characteristic size of caustic pattern. Moreover, by combining with the investigation of the fracture surface and the energy release rate analysis, the influence of aging time on the dynamic fracture behavior is discussed. Results show that the dynamic fracture toughness and critical energy release rate of PC decreases with aging time for short aging times, whereas they have little change or even increase for longer aging times. Therefore, aging modifies the mechanical properties especially the dynamic fracture properties of PC nonlinearly, not linearly as generally thought of.

Enthalpic Relaxation of Vital and Protease-Treated Wheat Gluten

Commercially available vital wheat gluten was purified with α-amylase and treated with protease in a one-step process. The supernatant of the protease-treated gluten was freeze dried, quench cooled, and aged for 2 weeks and analyzed using differential scanning calorimetry, sodium dodecyl sulfate poly-acrylamide gel electrophoresis, reverse phase high performance liquid chromatography, size exclusion high performance liquid chromatography, capillary zone electrophoresis, and dynamic mechanical analysis. The differential scanning calorimetry profile of the aged (un-purified or un-modified) gluten sample exhibited enthalpic relaxation beneath its glass transition (Tg) indicating molecular relaxation. Samples treated with 0.006 g protease/g gluten showed Tg at 49.11°C with ΔCp = 0.12 (J/°C g). Higher protease levels and longer aging time caused high Tg temperature, ΔCp, and ΔH of enthalpic relaxation. The size exclusion high performance liquid chromatography profile of the protease-treated gluten clearly showed differences in molecular size between the supernatant and the precipitate, while reverse phase high performance liquid chromatography profiles signified more hydrophilic gluten molecules than the control. The small difference in gluten molecular size after protease treatments (0.024 g protease versus 0.032 g) appeared to have a significant effect on the enthalpic relaxation, where the two treatments showed different degrees of enthalpic relation. The capillary zone electrophoresis data confirmed the insignificant difference between 0.024 and 0.032 g protease/g gluten regarding the size to charge ratio. The molecular interactions for protease-treated gluten were much weaker than vital gluten, as indicated by much weaker network and sensitivity to temperature, especially above Tg. The weaker network was evidenced by higher G″ versus G′, which explained the fluid like behavior of the protease-treated gluten.

Effects of T6 Age Hardening on Microstructure and Mechanical Properties of Al-Si-Cu Cast Aluminium Alloy

Effects of T6 artificial aging heat treatment on microstructure, microhardness and ultimate tensile strength of Al-4.93 wt% Si-3.47 wt% Cu alloy were investigated. The T6 age hardening treatment consists of solution treatment at 500±5°C for 8 hours followed by quenching into hot water at 80°C and artificial aging at 150, 170, 200 and 230°C for 1-48 hours followed by quenching into hot water. Microstructure was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). XRD and SEM revealed that the microstructure in the as-cast condition consists of primary dendritic α-Al, acicular-plate and globular forms of eutectic Si and intermetallic phases including globular Al2Cu and a flake-shape Al5FeSi. By T6 aging hardening, some intermetallics were dissolved and spheroidized. The volume fraction of eutectic phases in the as-cast, solution-treated, and solution-treated plus aging at 170°C for 24 hours is 17%, 12% and 10%, respectively. TEM results showed that precipitates in under-aging condition at 170° C for 6 hours are in the form of disc shape with the diameter in the range of 7-20 nm. At peak aging at 170°C for 24 hours, thin-plate precipitates with about 3-10 nm in thickness and 20-100 nm in length were found, lengthening to about 30-200 nm at longer aging time. The microhardness and ultimate tensile strength were increased from 71 HV0.05 and 227 MPa in the as-cast condition up to 140 HV0.05 and 400 MPa after solution treatment plus aging at 170°C for 24 hours, and decreased at prolong aging time.

Influence of Aging Time on Mg-8Al-1Zn-3Ca Alloy

The microstructure and mechanical properties of Mg-8Al-1Zn-3Ca magnesium alloy aged for different time are investigated. With the increase of aging time, the high melting point intermetallic compounds Al2Ca and Al4Ca are increased obviously in number and the phase of Mg17Al12 has a dramatic decrease in number. The longer aging time results in a significant segregation phenomenon. The second phase becomes coarsen, and mechanical properties decline.

Effect of aging time in vacuum on tenderness, and color and lipid stability of beef from mature cows during display in high oxygen atmosphere package

The effect of aging time in vacuum on tenderness, and lipid and color stability of modified-atmosphere packaged (MAP) beef during display was evaluated in eight Friesian mature cows. Longissimus thoracis et lumborum (LTL) sections were vacuum packaged and aged for 0, 3, 6, 8, 14 and 21days. After each aging time, the LTL sections were cut into steaks and packaged in high oxygen atmosphere (80% O2: 20% CO2). Meat shear force, and color and lipid stability were evaluated at 0, 3, 6, and 9days of simulated retail display. Aging for 6 or 8days improved beef tenderness with color stability, instrumental discoloration (R630–R580) and visual color evaluation in MAP similar to those of short-time aged (3d) or un-aged (0d) beef. Longer aging times (14 and 21d) resulted in tenderness values similar to those obtained with meat aged for 8days but affected negatively color and lipid stability and, consequently, reduced the shelf life of beef in MAP.

Aging Characteristics of RAP Blend Binders: Rheological Properties

AbstractA study involving two rolling-thin-film-oven–aged asphalts and their blends with 15 and 50% of extracted reclaimed asphalt pavement (RAP) binders was conducted to investigate the effect of RAP content and properties on the long-term aging characteristics of asphalt binders. The results from rheological analyses of aged, blended binders indicate that the aging characteristics of blended binders are dependent on fresh asphalt binders. The results show that the crossover frequency decreases at an exponential form as RAP concentrations increase, and the rheological index increases as RAP concentration increases. The pattern for stiffness increase as a function of aging times for RAP-blended binders is similar to that of a typical chemical-aging kinetic model, in which the stiffness increases substantially initially and then levels off at longer aging times. The results demonstrate that there is a linear relationship between the logarithm of G* and the phase angle for RAP-blended binders at all aging t...

The Effect of Indium Additions on Mg-Li and Mg-Li-Al Alloys

It is known that BCC Mg-Li alloys offer the opportunity to realize both high specific strength and good ductility in a light weight alloy. The commonest addition to this system is Al due to its solid solution-strengthening ability. This system is also known to precipitate a potent metastable phase that subsequently transitions to the equilibrium AlLi phase. There are other systems, Zn, Cd, and In, which are also known to precipitate a phase that is similar to the AlLi phase. Of these additions, the phase-evolution characteristics associated with adding In to Mg-Li and Mg-Li-Al alloys are largely unknown. This article seeks to understand the phase transformation, microstructural evolution, and mechanical behavior of In additions by systematically studying Mg-Li-In in contrast to Mg-Li-Al and Mg-Li-Al-In. This study represents an initial investigation of the Mg-Li-In system, while simultaneously determining Indium’s potential as a microalloying addition. It was found that in the compositional ranges under investigation, a metastable phase does form in each system, and at longer aging times, In3Li13 is found to precipitate. Commentary and insight are also provided with respect to precipitate nucleation and coarsening behavior.

Finite element analysis of long-time aging and sudden accidental degeneration of lumbar spine segments in compression

Finite element analysis of long-time aging and sudden accidental degeneration of lumbar spine segments in compression

Finite element analysis of long-time aging and sudden accidental degeneration of lumbar spine segments in compression

3D finite element analysis of long term aging and sudden accidental degeneration processes is presented for physiologic compression load. A systematic modeling and simulation is applied for analyzing the separated and mutual effect of certain material moduli of the components of lumbar motion segments on the mechanical behaviour and stability of the segment during the long time and sudden degeneration processes. It was concluded that due to their smallest stiffness the younger segments with light degeneration are the most vulnerable during both the long-time age-related and the sudden overload-related degeneration. DOI: 10.17489/biohun/2013/1/25

Enhancing the Organoleptic and Functional Properties of Jujube by a Quick Aging Process

Black jujube was made by aging dried jujube and its physiochemical characteristics, antioxidant activities and α-glucosidase inhibitory activities were evaluated. The moisture and sugar contents were increased depending on the period of aging times and the pH was reduced thereby increasing acidity. The color of black jujube extract was changed from red to black resulting in decreases of Hunter color values L, a and b. As the aging progressed, sucrose was decomposed by increasing glucose and fructose, indicating higher contents of the total reducing sugars. Among the six different types of organic acids extracted from dried jujube, the levels of oxalic acid and citric acid were increased as the aging progressed. The total polyphenol contents in ethanol and water extracts of dried jujube were 7.74 and 8.12 mg/g, respectively. The water extract of black jujube aged for 48 hr contained the highest polyphenol contents at 16.82 mg/g. The 5’-hydroxymethylfurfural (5’-HMF) contents of black jujube extract significantly increased by longer aging times, and contained higher contents in the ethanol extract than water extract. The ethanol extract of black jujube showed the highest 5’-HMF content with 338.89 mg% after aging for 3 days. Also, IC50 values of black jujube aged for 72 hr evaluated by DPPH and ABTS radical assays were 0.54 and 0.59 mg/mL, respectively. α-Glucosidase inhibitory activities of black jujube at the concentration of 3.33 mg/mL (ethanol extract) increased from 65 to 80 % after aging for 72 hr.

Evolution of size and shape of gold nanoparticles during long-time aging

The evolution of size and shape of gold nanoparticles was studied during long-time aging. The initial particle size of 2–5 nm increased to about 25 nm in one year of storage. It was revealed that the main mechanism of particle growth is Ostwald ripening, however, fusion of particles was also observed. Additionally, while the initial particles have spherical morphology, the grown particles show various shapes such as sphere, bipyramid, decahedron, deca-tetrahedron, triangular plate and rod. Twin boundaries with large frequency of ∼5% were detected inside the particles which have an important effect on the evolution of morphology. This study suggests that aging may be a new way of tuning size and shape of gold nanoparticles.

Microstructure evolution of T91 heat-resistant steels after long-time aging

To investigate the evolution of microstructure damage degree and the precipitated phases of heat-resistant metal in power plant under high temperature and stress environment, the high-temperature aging tests were conducted to investigate the aging behavior of T91 steel at different temperatures and stress. The optical microscopy, scanning electron microscopy, and transmission electron microscopy were used to investigate the structure and precipitated phases, the results showed that the orientation characteristics of tempered martensite was dispersed, and the grain size is obviously increased. The density of dislocation decreased with increasing temperature and stress. The important strengthening phase of M23C6 (M=Fe, Cr) was coarsened by the diffusion of main alloying elements Cr, while the smaller size MX (M=Nb,V; X=C, N) phase distributed in the grain is relatively stable in the aging.

EFFECT OF LONG-TERM AGING ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ALLOY C276

Nickel-based superalloy C276 had become one of the alternative materials in simulation loop of thorium molten salt reactor (TMSR) nuclear power system. The strength and plasticity decay of C276 alloy under high temperature environment for long time will directly threatened the security of simulation loop of TMSR. The microstructure of C276 alloy after long-term aging at 700 degrees C was studied by TEM and SEM with EDS, and the high temperature mechanical performance of C276 alloy after aging was researched at 700 degrees C with an universal high-temperature materials testing machine. At the same time, the morphology of tensile fracture was analyzed by SEM. The results show that massive block mu phase and M6C carbides are precipitated after long-term aging with 700 degrees C at the grain boundaries and within grains of C276 alloy, and the block precipitated phase grains grow up with aging time, some precipitated grains at boundaries extend forward the interior of based crystal. The alloy is strengthened by the effect of precipitation phase, so the strength is not reduced after long-term aging at 700 degrees C high temperature. As aging time increases, the plasticity of C276 alloy reduces firstly and then increases to the peak after aging 720 h, and decreases again. However, the plasticity of C276 alloy still maintain well after longer aging time. The high temperature tensile fracture mode of C276 alloy is ductile fracture after long-term aging.

CHARACTERISTIC AND MECHANISM OF PHASETRANSFORMATION OF GH4169G ALLOYDURING HEAT TREATMENT

By means of heat treatment at different regimes,microstructure observation and XRD analysis,an investigation has been made into the influence of heat treatment on the phases constitution and distribution regularity of GH4169G alloy.The results show that under the experimental conditions, microstructure of GH4169G alloy consists ofγmatrix,particle-likeγ',disc-likeγ andδphases,and the coherent interfaces are kept between the phases.Thereinto,microstructure of directional aging treatment ITF-DA-GH4169G alloy consists of a fewγ' phase,lots ofγ and 7 phases,however, long-time aging treatment ITF-DA-LTA-GH4169G consists of a fewγ',lots ofγ,γand needle-likeδphases.As the Nb atom diffuses into the lattice ofγ' phase during the aging treatment,γ'-Ni_3Al phase with L1_2 structure is transformed intoγ-Ni_3Nb phase with DO_(22) structure when the Nb and Ni atoms on(001) plane ofγ' phase migrate along 1/2(110) direction.With the growth ofγ phase during the long term aging,the given crystal plane in the new parallelepiped migrates along the 1/6(112) direction, which makes theγ phase transform intoδ-Ni_3Nb phase with DO_a structure.Moreover,theγ phase may grow up into the disc-like configuration along the c-axis direction due to the restriction of the a-and b-axis coherent interfaces.And it is a main reason that theδ-Ni_3Nb phase grows into needle-like configuration along the(100) plane due to the {200}_δplane ofδphase keeps coherent interface with {111}_γplane ofγmatrix phase.

Correlation of intermetallic compound growth behavior and melt state of Sn–3.5Ag–3.5Bi/Cu joint during soldering and isothermal aging

The intermetallic compound (IMC) growth behavior of Sn–3.5Ag–3.5Bi/Cu joint was investigated with a change in the solder melt structure during soldering and 180 °C isothermal aging. The results show that when the solders undergo liqiud–liquid structure transition (LLST), the IMC of the joint is thinner and more evenly distributed during soldering. The interface IMC is also thinner, and the quantity of Ag3Sn as well as Cu6Sn5 in the solder is relatively lower. However, the IMCs are more bulky after long-time aging at 180 °C. When the solders do not undergo LLST, microcracks form in the solder. Kirkendall voids are more abundant and interconnected after long, high-temperature aging. This finding indicates better joint reliability after than before LLST. The growth rate constants of the interface IMC for the two kinds of joints are calculated to be 1.94 × 10−12 and 9.71 × 10−13. The correlation of IMC growth behavior and melt state is analyzed from the viewpoints of LLST and atom diffusion.

Flexible fiber-shaped CuInSe2 solar cells with single-wire-structure: Design, construction and performance

Fiber-shaped solar cells (FSCs) have attracted increasing interest in recent years due to their numerous advantages. Herein we report the first prototype of highly flexible all-solid-state single-wire FSCs by using CuInSe2 (CIS) as the model photoactive semiconductor. CIS layer is electrodeposited on a flexible Mo wire as the substrate. Subsequently, CdS, ZnO and ITO layers are orderly deposited on the Mo/CIS wire, and each upper layer ensures full contact with the underlying layer, resulting in an excellent structural uniformity along circumference of the FSC. This Mo/CIS/CdS/ZnO/ITO single-wire FSC exhibits a power conversion efficiency of 2.31%, which is one of the highest values in all reported FSCs. More importantly, the present all-solid-state single-wire FSC exhibits stable conversion efficiency (2.16–2.32%) during rotation (0∼360°), bending (0∼360°) and long-time aging (stored at 60°C for 600h) processes, which makes it possible to fabricate very long single-wire FSC with stable efficiency for weaving large-area devices and/or the stereoscopic cell textiles. Our method provides a new and general approach for fabricating flexible single-wire FSC with various kinds of photovoltaic semiconductor materials, and it also would be applicable to develop other flexible electronic circuits.

The precipitation strengthening behavior of Cu-rich phase in Nb contained advanced Fe–Cr–Ni type austenitic heat resistant steel for USC power plant application

Copper has been used as a strengthening element in newly developed Fe–Cr–Ni type austenitic heat resistant steel for inducing Cu-rich phase precipitation to meet high temperature strength requirement for 600°C Ultra Super-Critical (USC) coal fired power plants for many years. However, the precipitation behavior and strengthening mechanism of Cu-rich phase in these advanced austenitic heat resistant steels is still unclear. In order to understand the precipitation strengthening behavior of Cu-rich phase and to promote high strength austenitic heat resistant steel development, 18 Cr9 NiCuNb steel which is a Cu-added Nb contained advanced Fe–Cr–Ni type austenitic heat resistant steel has been selected for this study to be aged at 650°C till to 10,000h. Micro-hardness and room temperature tensile test were conducted after long-time aging. SEM, TEM, HRTEM and three dimensional atom probe (3DAP) technology accompanying with thermodynamic calculation have been used to investigate the Cu-rich phase precipitation behavior during 650°C aging. The experimental results showed that Cu atoms can quickly concentrate in clusters at very early precipitation stage to form the fine nano-size Cu-rich “segregation areas” within less than 1h at 650°C. With increasing aging time at 650°C Cu atoms continuously concentrate to Cu-rich segregation areas (clusters) and simultaneously other kinds of atoms such as Fe, Cr and Ni diffuse away from Cu-rich segregation areas to austenitic matrix, and finally to complete the transformation from Cu-rich segregation areas to Cu-rich phase. However, there is only Cu atoms concentration but not crystallographic transformation from early stage of Cu-rich clusters forming to the final Cu-rich phase formation. Even the Cu atom becomes the main composed element after 500h aging at 650°C the Cu-rich phase still keeps coherent relationship with austenitic matrix. According the experimental results in this study, Cu-rich phase precipitation sequence which starts from the Cu atom segregation followed by the Cu diffusing from matrix to segregation areas and Fe, Cr and Ni atoms diffuse out from Cu-rich areas to matrix without crystallographic transformation is proposed. The Cu-rich phase is the most dispersed phase and contributes the most important strengthening effect among all precipitated phases (M23C6, MX and Cu-rich phase). It has been found that Cu-rich phase is very stable and still keeps in nano-size even for 10,000h aging at 650°C. The unique precipitation strengthening of Cu-rich phase in combination with nano-size Nb-rich MX phase and grain-boundary M23C6 carbide contributes excellent strengthening effect to 18 Cr9 NiCuNb austenitic heat resistant steel.

Characterizations of precipitate phases in a Ti–Ni–Pd alloy

The microstructure of 46Ti–37.5Ni–16.5Pd (at.%) alloy was investigated by electron diffraction and high-resolution scanning transmission electron microscopy. The phase content and stability were determined at several different temperatures and times. Aging at 400 °C for 1 h results in a new phase (P1-phase), which is consumed by P-phase at longer aging times. At 450 °C, the P1-phase appears first, and then coexists with P-phase. At 500 °C, the entire alloy transforms into the P1-phase. At 550 °C, Ti3(Ni,Pd)4 phase begins to form.

Phase transition hysteresis of ferroelectric Sr5EuTi3Nb7O30 ceramics with tetragonal tungsten bronze structure

The first-order ferroelectric transition of Sr5EuTi3Nb7O30 tungsten bronze ceramics was investigated together with the thermal history dependence of dielectric properties and differential scanning calorimetry (DSC) analysis. Moreover, the diffuse dielectric maximum appeared at a temperature above the ferroelectric transition, and this phenomenon had been reported in ferroelectrics with perovskite structure, but had never been observed in tungsten bronzes. Large hysteresis in the ferroelectric transition and severe depression of T0 were observed in both the permittivity-temperature and DSC curves, and were attributed to the complex nature of the tetragonal tungsten bronze structure. The DSC measurements were also used to get better insight into the gradual stability of the ferroelectric phase after cooling from the high temperature paraelectric phase. The abnormal splitting of the endothermic peaks was observed during the DSC measurements with lower start temperature or longer aging time. Two possible mechanisms were suggested. One was the separation of ferroelectric phase due to the compositional inhomogeneity. In another possible mechanism, the polar nanoregions coexisting with the ferroelectric domains were suggested and would possibly transit into the paraelectric phase at temperature below the ferroelectric transition.