Decreasing Aging Temperature Research Articles

The microstructure evolution and mechanical properties of Ti–1300 alloy during ECAP deformation and subsequent aging treatment

The effect of Equal channel angular pressing (ECAP) deformation on the microstructure, mechanical properties, and aging behavior of solution treated Ti–1300 alloy was investigated. The results show that the grains are not broken during ECAP deformation due to coordination of grain rotation. The dominant deformation mechanism involved dislocation slip and twinning. The ECAP deformation has a significant effect on the subsequent aging behavior. The microstructure of aged samples comprised αs phase in β matrix. The precipitation of αs phase in the pre-deformed sample is higher than that in the solution treated sample, which is reflected in the improvement of microhardness of the pre-deformed + aging sample. The microhardness of the alloy after ECAP deformation increases with decreasing aging temperature and increasing aging time.

Gradient microstructure and mechanical properties of Ti-6Al-4V titanium alloy fabricated by high-frequency induction quenching treatment

A gradient microstructure was successfully fabricated by high-frequency induction quenching treatment (HFIQT) to improve the mechanical behavior of Ti-6Al-4V alloy in this work. Microstructural evolution was systematically characterized by electron backscattered diffraction and transmission electron microscopy. The results showed that the gradient microstructure of the alloy after HFIQT and aging varied from a fine αs lamellae decomposed from α′-martensite at the surface layer to a bimodal microstructure at the center. Moreover, the alloy with gradient microstructure presents an optimal strength-ductility synergy. The tensile test results showed that a best strength plastic product UT of 12433.1 MPa·%, an ultimate strength of 1231 MPa and an elongation of 10.1 % were obtained after HFIQT for 5.2 s and aging at 400 °C for 6 h. The tensile strength of the alloy aged at 400 °C markedly increased with the increase in soaking time from 5.1 to 5.3 s during HFIQT. Meanwhile, the tensile strength of the alloy slightly increased with the decrease in aging temperature from 550 to 400 °C during HFIQT. Surprisingly, the elongation of the alloy also increased with decreasing aging temperature. The effects of the gradient microstructure characteristic on strength and ductility of the Ti-6Al-4V alloy were discussed.

Effect of Aging and Deformation Treatments on Mechanical Properties of Aluminum AA-6063

How the parameters of artificial aging heat treatments, in AA 6063 aluminum samples, previously solubilized and deformed in cold, influence on the mechanical properties of hardness and traction was investigated. The experiments followed the sequence: First, the solubilization treatment was carried out for 2h using prismatic specimens of 10mm thickness; then the samples were cold deformed with area reductions: 30% -60% -80%. Finally, the aging treatment was carried out on all samples, using temperatures: 150-250-350-450 °C, and holding times: 1-10-30-60-90-120 min. After aging the samples were machined according to the standards. The hardness was measured on the Vickers scale (HV) and the tensile tests followed the ASTM E 8M-95ª standard. Microscopy was performed at the optical and Electronic SEM level, complemented with an EDS analysis. It was found that the highest hardness values occur at 150 °C. The yield point YS increases as decreasing aging temperature, and decreases whith increasing deformation degree. The mechanical strength UTS increases as decreasing temperature and increasing whith deformation degree. Regarding the mechanical properties of traction, the optimal condition is found for the samples deformed at 80% and aged at 250 °C, presenting a (UTS) of 193 MPa, and 15% elongation. The samples with 80% reduction, aged at 450 °C for 120 min are those with the best recrystallization index. It would take a time greater than 120 min for the grains to thicken and the precipitates completely disappear to reach complete recrystallization. EDS analysis indicates the presence of Mg2Si precipitates and the β phase.

Effect of Sigma Phase Morphology on the Degradation of Properties in a Super Duplex Stainless Steel.

Sigma phase is commonly considered to be the most deleterious secondary phase precipitating in duplex stainless steels, as it results in an extreme reduction of corrosion resistance and toughness. Previous studies have mainly focused on the kinetics of sigma phase precipitation and influences on properties and only a few works have studied the morphology of sigma phase and its influences on material properties. Therefore, the influence of sigma phase morphology on the degradation of corrosion resistance and mechanical properties of 2507 super duplex stainless steel (SDSS) was studied after 10 h of arc heat treatment using optical and scanning electron microscopy, electron backscattered diffraction analysis, corrosion testing, and thermodynamic calculations. A stationary arc was applied on the 2507 SDSS disc mounted on a water-cooled chamber, producing a steady-state temperature gradient covering the entire temperature range from room temperature to the melting point. Sigma phase was the major intermetallic precipitating between 630 °C and 1010 °C and its morphology changed from blocky to fine coral-shaped with decreasing aging temperature. At the same time, the average thickness of the precipitates decreased from 2.9 µm to 0.5 µm. The chemical composition of sigma was similar to that predicted by thermodynamic calculations when formed at 800–900 °C, but deviated at higher and lower temperatures. The formation of blocky sigma phase introduced local strain in the bulk of the primary austenite grains. However, the local strain was most pronounced in the secondary austenite grains next to the coral-shaped sigma phase precipitating at lower temperatures. Microstructures with blocky and coral-shaped sigma phase particles were prone to develop microscale cracks and local corrosion, respectively. Local corrosion occurred primarily in ferrite and in secondary austenite, which was predicted by thermodynamic calculations to have a low pitting resistance equivalent. To conclude, the influence of sigma phase morphology on the degradation of properties was summarized in two diagrams as functions of the level of static load and the severity of the corrosive environment.

The kinetics of the glass transition and physical aging in germanium selenide glasses

The kinetics associated with the glass transition is investigated using differential scanning calorimetry (DSC) for germanium selenide glasses with Ge content ranging from 0 to 30at.% and average coordination numbers ranging from 2.0 to 2.6. As Ge content increases, the glass transition region broadens and the step change in heat capacity at Tg decreases. As a result of physical aging, enthalpy overshoots are observed in DSC heating scans and the corresponding change in enthalpy can be calculated as a function of aging time. The change in enthalpy linearly increases with the logarithm of aging time and then levels off at an equilibrium value that increases with decreasing aging temperature. The time required to reach equilibrium increases with decreasing aging temperature and, at a given distance from Tg, the time increases with decreasing germanium content. The results indicate that all samples show expected physical aging behavior, and no evidence is found for a Boolchand intermediate phase characterized by high stability and absence of physical aging.

Variation of Hardness with Microstructure Evolutions in Metastable β Titanium Alloy TIMETAL<sup>®</sup>LCB

Microstructure evolutions and hardness variation during aging in metastable β titanium alloy TIMETAL®LCB have been examined. In as-quenched specimen after solution treatment, athermal ω phase formed. Isothermal ω phase formed during aging at 623 K, and α phase formed after precipitation of isothermal ω phase during aging at 673 and 773 K. Alpha phase nucleated at isothermal ω phase, and had the orientation relationship with β and ω, (111)β//(0001)ω//(1120 )α and [10 1 ]β//[1120 ]ω//[0001]α . During aging at 873 K, α phase formed without isothermal ω phase. Hardness increased with increasing aging time and decreasing aging temperature, partly because number density of isothermal ω or α precipitates increased with increasing aging time and decreasing aging temperature.

Martensitic and magnetic transformations of Ni–Ga–Fe–Co ferromagnetic shape memory alloys

Effects of Co addition on the phase equilibria between the β (B2) and γ (A1) phases at 800 and 1000 °C and aging temperature dependence on the martensitic and magnetic transformation temperatures in Ni–Ga–Fe–Co alloys were examined with energy dispersion X-ray spectroscopy (EDX), differential scanning calorimetry (DSC) and vibrating sample magnetometry (VSM). The equilibrium compositions of Fe and Ga are little changed by the addition of Co, and Co tends to be distributed in the γ phase rather than in the β phase. The B2/L2 1 order–disorder and magnetic transformation temperatures increase with increasing Co content, while the martensitic transformation temperatures decrease. While the martensitic transformation temperatures monotonously decrease with decreasing aging temperature, the Curie temperature increases with the decrease of aging temperature in the high temperature region over 300 °C and then starts to decrease at low temperatures.

Glass transition and enthalpy relaxation of amorphous lactose glass

The glass transition temperature, T g, and enthalpy relaxation of amorphous lactose glass were investigated by differential scanning calorimetry (DSC) for isothermal aging periods at various temperatures (25, 60, 75, and 90 °C) below T g. Both T g and enthalpy relaxation were found to increase with increasing aging time and temperature. The enthalpy relaxation increased approximately exponentially with aging time at a temperature (90 °C) close to T g (102 °C). There was no significant change observed in the enthalpy relaxation around room temperature (25 °C) over an aging period of 1 month. The Kohlrausch–Williams–Watts (KWW) model was able to fit the experimental enthalpy relaxation data well. The relaxation distribution parameter ( β) was determined to be in the range 0.81–0.89. The enthalpy relaxation time constant ( τ) increased with decreasing aging temperature. The observed enthalpy relaxation data showed that molecular mobility in amorphous lactose glass was higher at temperatures closer to T g. Lactose glass was stable for a long time at 25 °C. These findings should be helpful for improving the processing and storage stability of amorphous lactose and lactose containing food and pharmaceutical products.

Aging response of Al–Zn–Mg–Cu spray formed alloys and their metal matrix composites

The aging response of various Al–Zn–Mg–Cu alloys was compared with the reinforced counterpart. The effects of aging temperature and time on the mechanical properties of these alloys, was also determined. Moreover, the effects of quenching rate from solution temperature, time between quench and aging, and heating rate to precipitation temperature were investigated. The study was executed by selecting two different heat treatments for each of three different aging temperatures: one without prior straining, and the other with 2% straining prior to aging to relieve stress. Room temperature tensile testing was conducted to determine these variations of aging on the strength of the spray formed Al–Zn–Mg–Cu alloys. The presence of SiC particles accelerated the aging kinetics of the alloys compared to the unreinforced counterparts. This difference in time to peak aging decreased with decreasing aging temperature. At uniform temperatures, differences for time to peak aging between unreinforced and composite alloys also existed in both the prestrained and unstrained condition. The difference was not as great in the prestrained state. The tensile strengths increased slightly with prestraining, but not significantly. Alloys containing silver maintained high strengths over silver-free counterparts when rapidly heated to precipitation temperatures above 120 °C. At slow heating rates, however, the silver-free alloys matched or were slightly higher than the strength of silver alloys, with increasing heating rate.

Accumulation of Free L-Glutamic Acid in Full- and Reduced-fat Cheddar Cheese Ripened at Different Time/temperature Conditions

Influence of ripening conditions on accumulation of free L-glutamic acid (FGA) in full (FF)- and reduced-fat (RF) Cheddar cheese was investigated. Cheeses were ripened isothermally at 5 and 8°C for 6 months; aged at 5 and 8°C for 1 and 2 months and then at 8 and 5°C, respectively, for 5 and 4 months, respectively; or aged for 1 and 2 months at the latter temperatures and then again at 5 or 8°C for 4 and 3 months, respectively. In all cases, accumulation of FGA correlated well with accumulation of soluble nitrogen-containing fractions of cheese and, for isothermally aged cheeses, was linearly related to cheese age. Results suggested that level of FGA might be considered a ripening index in both FF and RF Cheddar. Level of FGA in cheese ripened at 8°C was significantly higher than that in cheese ripened at 5°C and, at a given aging conditions, level of FGA in FF cheese was significantly lower than that in RF cheeses. Increasing or decreasing aging temperature by 3°C at different cheese ages resulted in cheese-specific FGA levels that differed significantly from those obtained with cheeses ripened isothermally at 8°C or 5°C. Accumulation of FGA was influenced by effects of aging conditions and cheese composition on cheese-age-specific proteolytic activities in cheese. Results suggested that small changes in aging temperature, at desired stages during aging, may offer opportunities in controlling and modulating rate and extent of proteolytic activities during cheese aging and thus provide tools to better modulate the development of cheese quality attributes.

Physical aging of an amorphous polyimide: Enthalpy relaxation and mechanical property changes

The physical aging behavior of an isotropic amorphous polyimide possessing a glass transition temperature of approximately 239°C was investigated for aging temperatures ranging from 174 to 224°C. Enthalpy recovery was evaluated as a function of aging time following sub-Tg annealing in order to assess enthalpy relaxation rates, and time-aging time superposition was employed in order to quantify mechanical aging rates from creep compliance measurements. With the exception of aging rates obtained for aging temperatures close to Tg, the enthalpy relaxation rates exhibited a significant decline with decreasing aging temperature while the creep compliance aging rates remained relatively unchanged with respect to aging temperature. Evidence suggests distinctly different relaxation time responses for enthalpy relaxation and mechanical creep changes during aging. The frequency dependence of dynamic mechanical response was probed as a function of time during isothermal aging, and failure of time-aging time superposition was evident from the resulting data. Compared to the creep compliance testing, the dynamic mechanical analysis probed the shorter time portion of the relaxation response which involved the additional contribution of a secondary relaxation, thus leading to failure of superposition. Room temperature stress-strain behavior was also monitored after aging at 204°C, with the result that no discernible embrittlement due to physical aging was detected despite aging-induced increases in yield stress and modulus. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1931–1946, 1999

Phase Separation and Lattice Misfit in NiAl(β<SUB>1</SUB>)–Ni<SUB>2</SUB>AlTi(<I>H</I>)–NiTi(β<SUB>2</SUB>) System

The lattice misfits at interphase interfaces, NiAl(B 2 )-Ni 2 AlTi(L2 I ) and Ni 2 AlTi(L2 I )-NiTi(B2), in a pseudobinary NiAl(B2)-NiTi(B2) system have been estimated by transmission electron microscopy. When the size of Ni 2 AlTi precipitates is smaller than a critical value, the precipitates keep their lattice coherency with the NiAI and NiTi matrices. After longer periods of aging the Ni 2 AlTi precipitates lose their coherency by introducing interface dislocations surrounding them. The coherency loss occurs catastrophically and the shape of the precipitates changes to a globular one after the loss of coherency, while keeping the cubic-cubic orientation relationship. Contrast experiments have revealed that the Burgers vectors of these misfit dislocations are of a type with the pure edge component lying nearby on the surface of the Ni 2 AlTi phase. The magnitudes of the lattice misfits at NiAl-Ni 2 AlTi and NiTi-Ni 2 AlTi interfaces have been estimated from the spacings of the misfit dislocations and found to increase with decreasing aging temperature in both the systems. The present results are compared with the previously reported theoretical and experimental values. A NiAl-NiTi pseudobinary phase diagram is proposed based upon microstructure observation, lattice misfit measurements and analytical electron microscopy.

Free-Volume Formation and Relaxation in a Poly(ethylene oxide)/Poly(methyl methacrylate) Blend I. Detection by the Spin Label Method

The electron spin resonance (ESR) line shape of nitroxide radical labels attached to poly(ethylene oxide) (PEO) chains in a blend with isotactic poly(methyl methacrylate) (PMMA) was studied. Two spectral components with different rates of motion, a “fast” component and a “slow” component ansing from the radicals, are observed. The ESR spectra observed at room temperature change substantially as a function of annealing and aging temperatures. The fractional amount of the fast component (mobile fraction) was estimated from the ESR spectra. (1) When the blend is annealed at temperature above 23°C, the mobile fraction increases in the lower temperature range and decreases in the higher temperature range. These phenomena can be attributed to phase separation and molecular mixing. (II) When the blend is phase-separated and subsequently aged at temperatures below 23°C, surprisingly the mobile fraction decreases with decreasing aging temperature around −13°C. When the sample is again annealed above 23°C, the mobile fraction increases abruptly at 60°C. These phenomena can be attributed to free-volume relaxation and formation. Relaxation phenomena should come from different rates of molecular motion of PMMA and PEO chains in the phase. The ESR spectra of nitroxide labels attached to PMMA chains in the blend support the conclusions.

Free-Volume Formation and Relaxation in a Poly(ethylene oxide)/Poly(methyl methacrylate) Blend II. Structural Relaxatron and Volume Change

The electron spin resonance (ESR) line shape of nitroxide radical labels attached to poly(ethylene oxide) (PEO) chains in a blend with isotactic poly(methyl methacrylate) (PMMA) of higher molecular weight than that in Part I of this series was studied as a function of aging and annealing temperatures. Two spectral components with different rates of motion, a “fast” component and a “slow” component arising from the radicals, are also observed. The fractional amount of the fast component (mobile fraction) observed at 27°C changes with aging and annealing temperatures. The fraction decreases abruptly around −15°C with decreasing aging temperature, whereas the fraction increases abruptly around 50°C with increasing annealing temperature. The specific volume of the blend was measured at 27°C by the dilatometric method. ca. 0.5% of volume contraction and expansion during aging at −15°C and annealing at 50°C, respectively were observed, attributed to relaxation related to free-volume formation and relaxation in an amorphous region of the blend.

Physical aging of a polyetherimide: Creep and DSC measurements

AbstractCreep and differential scanning calorimetry (DSC) measurements have been used to study the physical aging behavior of a polyetherimide. Isothermal aging temperatures ranged from 160°C to Tg with aging times ranging from 10 min to 8 days. The only measurable effect of physical aging on the short‐time creep curves is a shift of the creep compliance to longer times. Andrade plots of the compliance versus the cube root of time are linear at short times with the slope β decreasing with increasing aging time to a constant value once equilibrium is reached. Log β3 is related directly to the degree to which the creep curves shift to longer times with physical aging, and is used in this work as a measure of physical aging. A reduced curve of log β3 versus log aging time is obtained for the aging temperatures investigated by appropriate vertical and horizontal shifts. The enthalpy change during aging increases linearly with the logarithm of the aging time, ta, leveling off at equilibrium at values which increase with decreasing aging temperature. Hence, both nonequilibrium and equilibrium temperature shift factors can be calculated from the DSC data. Good agreement is observed between the equilibrium temperature shift factors obtained from the creep and DSC data. The temperature dependence of the nonequilibrium temperature shift factors is found to be an order of magnitude smaller than that of the equilibrium shift factors. The time scales to reach equilibrium for enthalpy and for mechanical measurements are found to be the same within experimental error. © 1995 John Wiley & Sons, Inc.

Direct synthesis of trans-polyacetylene films : Dependence on polymerization conditions

We tried to prepare trans-polyacetylene films without thermal treatment to obtain the films with conjugated system of long average length and narrow distribution. Polymerization was carried out at room temperature on various conditions. It has been clealy suggested that the decrease in polymerization rate particularly by decreasing aging temperature is effective for the preparation of trans-polyacetylene films without thermal treament.

Decomposition of Fe-Ni martensite: Implications for the low-temperature (≤500 °C) Fe-Ni phase diagram

The low-temperature (<500 °C) decomposition of Fe-Ni martensite was studied by aging martensitic Fe-Ni alloys at temperatures between 300 °C and 450 °C and by measuring the composition of the matrix and precipitate phases using the analytical electron microscope (AEM). For aging treatments between 300 °C and 450 °C, lath martensite in 15 and 25 wt pct Ni alloys decomposed with γ [face-centered cubic (fcc)] precipitates forming intergranularly, and plate martensite in 30 wt pct Ni alloys decomposed with γ (fcc) precipitates forming intragranularly. The habit plane for the intragranular precipitates is {111}fcc parallel to one of the {110}bcc planes in the martensite. The compositions of the γ intergranular and intragranular precipitates lie between 48 and 58 wt pct Ni and generally increase in Ni content with decreasing aging temperature. Diffusion gradients are observed in the matrix α [body-centered cubic (bcc)] with decreasing Ni contents close to the martensite grain boundaries and matrix/precipitate boundaries. The Ni composition of the matrix α phase in decomposed martensite is significantly higher than the equilibrium value of 4 to 5 wt pct Ni, suggesting that precipitate growth in Fe-Ni martensite is partially interface reaction controlled at low temperatures (<500 °C). The results of the experimental studies modify the γ/α + γ phase boundary in the present low-temperature Fe-Ni phase diagram and establish the eutectoid reaction in the temperature range between 400 °C and 450 °C.

Heat treatment of titanium alloy VT22

1. Characteristics of the mechanical properties of titanium alloy VT22 are found to be nonlinearly dependent on the heat-treatment parameters. As a rule, the strength increases, and the plasticity decreases with increasing temperature of the first step, the heating temperature for quenching, and the cooling rate, and with decreasing aging temperature. 2. Effects of the paired interaction between the heat-treatment parameters under investigation, i.e., the dependence of the effect of each of the parameters in vestigated on the level of the other parameters, are characteristic for alloy VT22. 3. Alloy VT22 is hardened during heat treatment at low cooling rates (but no lower than 3.5°C/min). 4. Computational equations are proposed for adjustment of the aging temperature during the heat treatment of welded subassemblies.

Crystallization characteristics of flon gas hydrates used as cool storage materials.

Crystallization tests of the hydrates of flon-12, flon-11 and flon-21 were carried out.The degree of supercooling (the difference between the critical decomposition temperature and the crystallization temperature of the gas hydrate) was decreased with decreasing aging temperature at which the flon-water mixtures were kept with agitation for a given period before cooling. The aging period did not affect the degree of supercooling. The agitation rate seemed to have no effect on it. The relationship between the degree of supercooling and the aging temperature was determined.

1087. Dislocation structures in dehydrogenated niobium: M Amano and Y Sasaki,Phys Stat Sol (a), 19 (2), 1973, 405–414

The aging response of various Al–Zn–Mg–Cu alloys was compared with the reinforced counterpart. The effects of aging temperature and time on the mechanical properties of these alloys, was also determined. Moreover, the effects of quenching rate from solution temperature, time between quench and aging, and heating rate to precipitation temperature were investigated. The study was executed by selecting two different heat treatments for each of three different aging temperatures: one without prior straining, and the other with 2% straining prior to aging to relieve stress. Room temperature tensile testing was conducted to determine these variations of aging on the strength of the spray formed Al–Zn–Mg–Cu alloys. The presence of SiC particles accelerated the aging kinetics of the alloys compared to the unreinforced counterparts. This difference in time to peak aging decreased with decreasing aging temperature. At uniform temperatures, differences for time to peak aging between unreinforced and composite alloys also existed in both the prestrained and unstrained condition. The difference was not as great in the prestrained state. The tensile strengths increased slightly with prestraining, but not significantly. Alloys containing silver maintained high strengths over silver-free counterparts when rapidly heated to precipitation temperatures above 120 °C. At slow heating rates, however, the silver-free alloys matched or were slightly higher than the strength of silver alloys, with increasing heating rate.