Low-temperature Aging Treatment Research Articles

Effect of Aging on the Precursor Sol for the Synthesis of Nanocrystalline ZSM-5

Nanocrystalline ZSM-5 (Si/Al = 100) is synthesized from an initial clear solution of TEOS-TPAOH-AIP-H2O system. The method comprises three stages: (i) concentration of an initial clear solution, (ii) low-temperature aging (25°C, 50°C, 75°C, or 100°C), and (iii) high-temperature hydrothermal treatment (180°C for 90 min). The average size of the crystals is almost the same when the aging temperature is in the range from 25°C to 75°C, i.e., around 48 nm. However, the average size of the zeolite crystals increases as the aging temperature reached 100°C, to 85 nm.

The effect of low temperature aging on the mechanical property & phase stability of Y-TZP ceramics

STATEMENT OF PROBLEMRecently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported.PURPOSEThe objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning electron microscope (SEM).MATERIAL AND METHODSY-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad Säckingen, Germany) were prepared in 40 mm (length) × 4 mm (width) × 3 mm (height) samples. Specimens were artificially aged in distilled water by heat-treatment at a temperature of 75, 100, 125, 150, 175, 200, and 225℃ for 10 hours, in order to induce the phase transformation at the surface. To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model 3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute, USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant differences (α= .05).RESULTSThe mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied aging temperature at below 125℃ for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above 150℃, the flexural strength started to decrease. Although low temperature aging caused the tetragonal-to-monoclinic phase transformation related to temperature, the minimum flexural strength was above 700 MPa.CONCLUSIONThe monoclinic phase started to appear after aging treatment above 100℃. With the higher aging temperature, the fraction of monoclinic phase increased. The ratio of monoclinic/tetragonal + monoclinic phase reached a plateau value, circa 75% above 175℃. The point of monoclinic concentration at which the flexural strength begins to decrease was between 12% and 54%.

Low temperature aging effects on the formation of Sn nanoclusters in SiO2∕Si films and interfaces

The formation of Sn nanocrystals (NCs) in ion implanted SiO2∕Si films is investigated using Rutherford backscattering spectrometry and transmission electron microscopy. Low temperature and long time aging treatments followed by high temperature thermal annealings lead to the formation of a dense bidimensional NC array located at the SiO2∕Si interface. This behavior is discussed considering the formation of small Sn clusters with a significantly improved thermal stability. The present experimental results are in good agreement with recent theoretical predictions that small Sn clusters can have their melting temperature enhanced in more than 1000°C.

Large enhancement in mechanical properties of the 6061 Al alloys after a single pressing by ECAP

Abstract The equal-channel angular pressed (ECAPed) 6061 Al alloys processed with various pre- and post-ECAP heat treatments were compared in terms of the balance between strength and tensile ductility, and it was concluded that the post-ECAP low-temperature aging treatment was most effective in improving the strength whilst retaining a moderate level of tensile ductility.

Precipitation Behavior during Ageing Treatment of a Single Crystal Nickel-Base Superalloy

The precipitation behavior during ageing treatment of a single crystal nickel-base superalloy was investigated by SEM and TEM. The results showed that tetragonal needle-like σ phase and blocky -W phase precipitated during low temperature ageing treatment after this testing alloy was completely solution heat treated. σ and -W phases robbed of solid solution strengthening alloying element W、Mo in the matrix and degraded high temperature creep rupture property severely. The creep curve of the crystal tested at 1010 °C and 248 MPa exhibited that the steady state creep rate ε was as high as 9.46 × 10-3/h. The creep-rupture life was only 25 hours. -W phase was not formed by decrease of W content properly. A relatively low level of Co could inhibit σ phase precipitation and improve microstructural stability.

Optimization of strength and ductility of 2024 Al by equal channel angular pressing (ECAP) and post-ECAP aging

Equal channel angular pressing (ECAP) in the solid solution state with post-ECAP low-temperature aging treatment was found to be quite effective in enhancing the mechanical properties of 2024 Al alloy. Yield stress (YS) as high as 630 MPa could be achieved. Moreover, the ductility of ECAPed alloy was improved after the aging treatment.

Ａｌ‐Ｍｇ‐Ｓｉ系合金のセレーションに及ぼす低温時効と復元処理の影響

In order to investigate effects of low temperature aging and reversion treatment on the serration of 6061 aluminum alloys, the reversion at from 423 to 853 K was conducted for the specimens in which the serration disappeared with the preliminary aging at 403 K. The measurements of electrical resistivity, DSC analysis and TEM micrographs showed that the solute atom concentration for the reversed specimens in which the serration generated again decreased remarkably due to formation of the precipitates, such as GP–zone, random-type, β″–phase, β′–phase and β–phase. Therefore, it was suggested that the disappearance of the serration was not affected by decrease of the solute atom concentration.

Use of pyrolysis-GC–MS to assess the thermal degradation behaviour of polymers containing chlorine II. Thermal stability characteristics of Neoprene/chlorobutyl rubber composites, before and after artificial ageing

Some composites containing a cross-linked blend of Neoprene and “chlorobutyl rubber” have been artificially aged at temperatures of 35 and 80°C for up to 3 months. Overall rate constants for their degradation at 387°C, before and after the ageing, have been measured by pyrolysis-GC–MS in order to assess whether the ageing has had any effect on their thermal stability. The results show that the low-temperature ageing treatment has caused no detectable deterioration in the thermal stability of the composites as measured at the higher temperature. The mean value of the first order rate constant, determined from a reproducibility test using 21 data points, is 0.0205±0.0036 s −1 at 387°C (68% confidence limit). The scatter is attributed to macro inhomogeneity in the composition of the samples. With respect to the different batch samples, the mean values of the specific rates of degradation of the two samples were found to lie within the standard deviation of the overall scatter. The effects of the artificial ageing have also been assessed by comparing the resolved gas chromatograms of the many products obtained from the 387°C pyrolyses of the control and the aged samples. These chromatograms are virtually identical, and this suggests that not only is the thermal stability unaffected, but also that the detailed mechanisms of the degradation have not changed with ageing. Mass spectra and mass chromatograms have also been examined in order to assess the general structures present within the wide variety of degradation products. High-yield low molecular weight components include isomeric butenes (butene-1, butene-2, and 2-methyl-propene-1), but it is difficult to distinguish between these because of the similarities in their mass spectra. There is also evidence for oligomeric butenes and many other aliphatic hydrocarbons (both saturated and unsaturated, linear and cyclic) with molecular weights up to several hundred. Other products include hydrogen chloride and chlorinated hydrocarbons, plus a few other hetero-compounds which can be related to known minor additives in the composites. Hydrogen chloride has also been established as a product at its detection limit when 100 μg of the chlorobutyl rubber component alone were heated at 100°C for 10 s, despite the fact that this material contains less than 2 wt% of chlorine.

Microstructural evolution during tempering of a multiphase steel containing retained austenite

Double cycle heat treatment has been imparted to a low carbon low alloy steel with a view to maximize volume fraction of retained austenite. ε-Carbide has been found to occur in the austenite phase. Its unusual presence has been explained as a result of enrichment by interstitials during isothermal holding. The steel has been subjected to low temperature ageing treatment to assess the stability of retained austenite against thermal severity. Retained austenite phase remained stable up to a temperature of 100°C. Decomposition of the austenitic phase having predominantly chunky morphology commenced at and above 200°C. Tempering at a temperature of 300°C led to the rearrangement of dislocations into parallel arrays. The mismatch between parent austenite and product ferrite phase resulted in the formation of interfacial dislocations. Upon tempering at 400°C, ε-carbide gave way to the formation of ε′(η)-carbide. The observation is extraordinary in view of low carbon content of the steel. Tempering at 500°C eventually led to the formation of stable cementite. Thus a sequence of events leading to the precipitation of cementite (θ) from parent austenite phase can be traced as: γR→α+ε→α+ε′η→α+θ

Properties of friction-stir-welded 7075 T651 aluminum

Friction stir welding (FSW), a new welding technique invented at TWI, was used to weld 7075 T651 aluminum, an alloy considered essentially unweldable by fusion processes. This weld process exposed the alloy to a short time, high-temperature spike, while introducing extensive localized deformation. Studies were performed on these solid-state welds to determine mechanical properties both in the longitudinal direction, i.e., within the weld nugget, and, more conventionally, transverse to the weld direction. Because of the unique weld procedure, a fully recrystallized fine grain weld nugget was developed. In addition, proximate to the nugget, both a thermomechanically affected zone (TMAZ) and heat affected zone (HAZ) were created. During welding, temperatures remained below the melting point and, as such, no cast or resolidification microstructure was developed. However, within the weld nugget, a banded microstructure that influences room-temperature fracture behavior was created. In the as-welded condition, weld nugget strength decreased, while ductility remained high. A low-temperature aging treatment failed to fully restore T651 strength and significantly reduced tensile ductility. Samples tested transverse to the weld direction failed in the HAZ, where coarsened precipitates caused localized softening. Subsequent low-temperature aging further reduced average strain to failure without affecting strength. Although reductions in strength and ductility were observed, in comparison to other weld processes, FSW offers considerable potential for welding 7075 T651 aluminum.

Effect of Low Temperature Ageing on the Transformation Behaviour of Near-Equiatomic NiTi

A unique three-stage transformation behaviour on cooling has been observed in a Ti-50.2 at% Ni alloy after a low temperature ageing treatment. The cooling transformation in the aged alloy occurred as a three-stage process of austenite-to-R phase transition followed by two separate martensitic transformations. The R phase transition developed during ageing with a clear second order nature initially and gradually evolved into a predominantly first order process. The occurrence of the R transition is not associated with a decrease in the martensitic transformation temperature during ageing. The reverse transformation to austenite occurred in one step, regardless of the nature of the forward transformation on cooling. An all-round shape memory effect was observed in aged samples. These experimental observations suggest that precipitation induced by the ageing treatment is responsible for the unusual transformation behaviour.

Up-quenching effect on the stabilization process of a CuZnAl martensite

Abstract The correlation between the recovered shape memory capability and the temperature of an up-quenching treatment of a partially stabilized martensite has been studied in a Cu-25.6wt.%Zn-3.94wt.%Al alloy by estimating the transformation temperatures M ∗ and A ∗ , the spacing difference Δd and the mechanical behaviour of tensile testing ( σ y , η an , η tr and η pl ). The effect of a subsequent secondary low temperature aging on the shape memory effect (SME) of an up-quenced stabilized martensite has also been investigated. It is shown that the transformation temperatures M ∗ and A ∗ decrease monotonically with increasing upquenching temperature, and secondary low temperature aging restores M ∗ and A ∗ to their original values with neither a change in Δd nor degradation of the shape recovery capability. It was also discovered that the up-quenched microstructure could change from the parent phase into a martensite phase as the result of a secondary low temperature aging treatment, which is correlated with the degree of short-range disorder in the DO 3 phase. Both the value of Δd and the capacity of the SME of a partially stabilized martensite can be restored by up-quenching in an oil bath with a temperature above 140°C for 3 min. However, up-quenching at 270°C causes a dramatic increase in yielding stress that is seriously detrimental to the SME behaviour of the sample owing the precipitation of α 1 plates.

Defect structures in low stacking fault energy CuGe solid solutions

The defects present in metastable CuGe alloys after slow cooling or quenching from the solution temperature have been investigated by conventional electron microscopy techniques. The defect configurations present after low temperature aging treatments designed to avoid the onset of h.c.p. phase precipitation have also been studied. The principal defects in slowly cooled alloys are intrinsic stacking faults bound by Shockley partials, whereas quenched alloys exhibit more “ragged” Shockley partials and “black spot” defects. Excess vacancies or vacancy-solute clusters present after quenching migrate during aging to form defects, the exact nature of which could not be identified for temperatures below 200 °C but were identified as stacking fault tetrahedra as the aging temperature was raised. Defect-free zones were observed adjacent to grain boundaries, non-coherent annealing twin boundaries and some partial dislocations, indicating that such regions can act as effective sinks for vacancy annihilation.

Corrosion behavior of 25 Pct Cr duplex stainless steel in CO2-H2S-Cl− environments

The corrosion behavior of duplex stainless steels in sour gas well environments was studied by examining the effects of environmental factors and alloying elements on their susceptibility to stress corrosion cracking and weighted-loss corrosion in CO/sub 2/-H/sub 2/S-Cl/sup -/ atmospheres. The results indicated that DP3 duplex stainless steel has an excellent work-hardening property compared with austenitic Type 317L stainless steel. Moreover, DP3 is resistant to SCC in CO/sub 2/-Cl/sup -/ environments up to temperatures of 480/sup 0/F. The presence of H/sub 2/S and cold working, however, make it more sensitive to cracking. Incorporating Cr, Ni, and Mo into duplex stainless steels increases the corrosion resistance in these environments. Duplex stainless steels that are composed of 3% Mo and 6% Ni maintain the corrosion resistance in high-temperature CO/sub 2/-Cl/sup -/ conditions, even after low-temperature aging treatment.

Influence of Heat Treatment on the Sensitization of 18Cr-2Mo-Ti Stabilized Ferritic Stainless Steel

The intergranular corrosion behavior of 18Cr-2Mo-0.6Ti ferritic stainless steel in the modified Strauss test was investigated as a function of the initial high temperature annealing treatment and subsequent low temperature aging treatments. When heat treated above 1100 °C, transmission electron microscopy studies indicate the Ti(C,N) begin to dissolve. During rapid cooling, (Ti,Cr) (C,N) precipitates intergranularly, the ratio of Cr/Ti intergrated intensities being ~ 1/3. During low temperature aging (<-550 °C), the (Ti, Cr)(C,N) grow, the Cr/Ti intergrated intensity ratio increases to ~1/2, and the alloy is susceptible to severe intergranular corrosion. When samples annealed at 1200 °C/1 h are heat treated at 800 to 900 °C, the equilibrium Ti(C,N) are reformed and subsequent low temperature aging treatments do not sensitize the alloy.

Effects of pre-irradiation treatments and minor composition modification on neutron irradiation embrittlement of 316 stainless steel

The effects of the combination of heavy cold work and low temperature aging (873–1073 K, 100 h), and minor composition modification on the irradiation embrittlement of 316 stainless steel were investigated. The samples were irradiated by JMTR at JAERI to the dose level of 2.5 × 10 24 n/m 2 (E > 1 MeV) at 823 and 923 K and tensile tested between R.T. and 1023 K. The embrittlement was compared from the standpoint of ductility survival ratio. The lowering of carbon content caused severer high temperature helium embrittlement in the solution treated condition. The heavy cold work and low temperature aging treatments could not improve the high temperature embrittlement compared with the solution treated condition. Titanium addition was beneficial especially for the reduction of the irradiation temperature sensitivity to the high temperature ductility.

A quench-age method for the fabrication of Nb(Al) superconductors

The possibility of taking advantage of the extended, high temperature solid solubility of Al in Nb in order to produce composite Nb-Nb 3 Al superconductors was investigated. Rapid quenching after an elevated (1950°C) solution treatment makes it possible to retain at room temperature a metastable solid solution containing up to 21 at.% Al. The solid solution transforms into the A-15 phase in the course of a short and relatively low temperature(1000°C) aging treatment. The inductively measured onset of superconductivity was 17.6 K in a 100 μm thick core of Nb 3 Al embedded in a Nb matrix and prepared by the quench-age method.