Double Heat Treatment Research Articles

Nucleation and growth in amorphous (GeS2)0.9(Sb2S3)0.1 thin films

The rates of isothermal nucleation and growth in chalcogenide glass thin films of (GeS2)0.9(Sb2S3)0.1 were studied using optical microscopy. Nucleation data was obtained from double stage heat treatment, followed by image analysis of polarized optical micrographs. The applicability of classical nucleation theory (CNT) to the nucleation data has been discussed. The growth data, corrected for viscosity suggest interface controlled 2D nucleated growth of β-GeS2 crystals. The isothermal curves of nucleation and growth determined by CNT and 2D nucleated growth model, respectively were found to be weakly intersecting. The nucleation curve had maxima at 350°C, which is below the glass transition temperature, while the growth curve had a peak at 439°C.

Effect of thermal cycle on microstructure and mechanical properties of CLAM steel weld CGHAZ

Based on the previous work of SHCCT diagram developing of China low activation martensitic (CLAM) steel, the effect of thermal cycle on the microstructure and mechanical properties of CLAM steel weld is investigated using physical thermal simulation (Gleeble 3500) to control heat input accurately. Three conditions including single layer, double layer welding and post-weld heat treatment (PWHT) are involved. The results show that higher cooling rate leads to better grain refinement but higher hardness in the coarse grained heat affected zone. Precipitation of delta ferrite is relatively severe when the cooling rate is low. Thermal cycle during double layer welding has an obvious weakening effect on mechanical properties, which mainly results from the larger quantity of delta ferrite precipitates. The microstructure and mechanical properties of CLAM steel joints can be improved by PWHT. Hardness of heat-affected zone tends to keep uniform with the increase of tempering temperature.

Solutioning and Aging of MAR-M247 Nickel-Based Superalloy

Despite the existence of previous studies on the heat treatment of the MAR-M247 superalloy, there is a lack of microstructural characterization data that support the heat-treatment conditions that are proposed in this study. Thus, the aim of this study is to investigate the changes in microstructure that occur in this alloy when subjected to different solutioning and aging heat treatments. Thermodynamic calculations and differential thermal analysis guided the experimental design and the analysis of experimental results. The MAR-M247 superalloy was produced via vacuum induction melting and investment casting. The samples were solutioned between 1185 and 1270 °C and aged between 770 and 980 °C. The as-cast and heat-treated samples were characterized using scanning electron microscopy in backscattered electron and secondary electron modes. Thermodynamic calculations have shown that the minimum solutioning temperature is approximately 1220 °C, occurring in a γ + MC + MB2 three-phase field (M = metal). The samples were solutioned at 1250 °C for 310 min before aging heat treatment. During solutioning the carbide composition is the MC phase shifts to higher hafnium (Hf) and lower tantalum (Ta) content, which is in agreement with the thermodynamics calculations. After solutioning, residual aluminum (Al) segregation leads to the formation of large γ′ particles in certain regions of the material following one-step aging heat treatment at 770 and 870 °C. However, a nearly uniform size distribution of γ′ particles was observed after aging at 980 °C as well as after double aging heat treatment at 980 °C for 300 min + 870 °C for 1200 min.

Dehydrated egg white: An allergen source for improving efficacy and safety in the diagnosis and treatment for egg allergy

Raw and cooked eggs are used as allergens in oral food challenge (OFC). Raw egg is the best option, as it keeps proteins intact and retains their allergenicity, albeit microbiologically safe manipulation is difficult. Therefore, the use of dehydrated egg white (DEW) could improve the efficacy and safety profile of OFC. The aim of the study was to compare the allergenicity of DEW, a product that undergoes a double heat treatment (pasteurization and drying), with that of raw egg white (REW) and determine the efficacy of DEW in the diagnosis of egg allergy. We conducted a prospective study of 40 egg-allergic patients who visited our outpatient clinic. Each patient underwent OFC with DEW and REW to determine the correlation between the tests. DEW and REW extracts were analyzed using SDS-PAGE. We compared the allergenicity of both extracts using IgE immunoblotting with a serum pool from patients with positive OFC results. Ten patients (25%) had positive OFC results with both DEW and REW, and the doses that triggered an allergic reaction in each patient were similar (p>0.05). All 30 patients (75%) with a negative OFC result with DEW also had negative OFC results with REW. SDS-PAGE and IgE immunoblotting revealed that the protein composition and IgE-binding capacity of both extracts were virtually identical. This is the first time that it is shown that the allergenicity of commercially available DEW is equivalent to raw egg whites. In vivo and in vitro tests showed that processing of DEW does not affect the allergenicity of egg proteins. DEW is an effective and microbiologically safer source of allergen for the diagnosis of egg allergy. Furthermore, DEW can be used in egg oral immunotherapy.

Single and double stage sintering of mechanically alloyed powder for nanostructured Ti6Al4V foams usable in cancellous scaffolds

Mechanical alloying and sintering were used to fabricate nanostructured Ti6Al4V scaffolds of highly controllable pore geometry and fully interconnected porous network. Elemental powders were milled for different periods of time (10, 20, 30, 40 and 60 h), mixed with 40–60 vol.-% of 200–400 μm cuboidal NaCl, compacted at 500–600 MPa and sintered according to single or double stage heat treatment regimes at 790 and 950°C under vacuum. After sintering, the samples were soaked in distilled water to washout the NaCl. Foamy microstructures were obtained showing well shaped biopores and fragmentary embedded micropores. The shape of initial NaCl was copied into the biopores which had highly interconnected architecture considered suitable for cancellous bone tissue adherence and cell culture.

Microstructure of TC21 Titanium Alloy after Superplastic Deformation and Heat Treatment

The isothermal constant strain rate tensile tests of the TC21 titanium alloy were conducted by SSAN-CMT4104 electronic tensile testing machine at different temperature. After superplastic deformation, the alloy was treated with double annealing heat treatment, and microstructure of the alloy was analyzed. The results show that dynamically recrystallization occurs during the superplastic tensile deformation. The primary α-grains aggregated and merged to form new crystal grains with irregular grain boundaries. The amount and morphology of primary α phase change gradually with the increasing of temperature. The alloy has duplex microstructure composed of primary α phase and different forms of β-transformed structure after superplastic deformation and double annealing. At deformation temperature of 930°C, the basket weave structure with equiaxed α phase appears.

Microstructure and hardness evolution in MAR-M247 Ni-based superalloy processed by controlled cooling and double heat treatment

This work studies the microstructure and hardness evolution in MAR-M247 Ni-based superalloy processed by controlled cooling and double heat treatment. The solidification experiments with controlled cooling rates in the range of 0.25–10K/s were carried out using GLEEBLE thermo-mechanical simulator. In the as-solidified material, with increasing cooling rate, grain and carbide size decreased, whereas volume fraction of carbides and microhardness increased. The as-solidified samples were subjected to a double heat treatment consisting of solution treatment followed by aging. The double heat treatment did not affect much the microstructure evolved in the sample solidified at 0.25K/s while it led to dissolution of the γ/MC eutectic in the samples solidified with the cooling rates of 5 and 10K/s. No significant effect of the double heat treatment on grain size, size and volume fraction of carbides is seen in all samples. The processing – microstructure–microhardness relationship in the material is discussed.

Promoting Bacillus cereus spore germination for subsequent inactivation by mild heat treatment.

Sublethal heat treatment may activate dormant spores and thereby potentiate the conversion of spores to vegetative cells. As the germinated spore is known to possess lower heat resistance than its dormant counterpart, it has been postulated that double heat treatment, i.e., spore heat activation followed by germination and then by heat inactivation, can be used to control spores in foods. Production of refrigerated processed foods of extended durability often includes more than one heat treatment of the food components. This work simulates conventional heat treatment procedures and evaluates double heat treatment as a method to improve spore control in model food matrixes of meat broth and cream sauce. Bacillus cereus NVH 1230-88 spores were supplemented in food model matrixes and heat activated at 70°C and then heat inactivated at 80 or 90°C. The samples were held at 29 to 30°C for 1 h between primary and secondary heat treatments, to allow spore germination. Nutrients naturally present in the food matrixes, e.g., amino acids and inosine, could act as germinants that induce germination. The levels of germinants could be too low to produce effective germination within 1 h. Following primary heat treatment, some samples were therefore supplemented with a combination of L-alanine and inosine, a germinant mixture known to be effective for B. cereus spores. In both matrixes, a combination of double heat treatment (heat activation, germination, and inactivation) and addition of germinants gave a reduction in spore counts equivalent to or greater than that obtained with a single heat treatment for 12 min at 90°C. Addition of germinants was essential to induce effective germination in cream sauce during 1 h at 29 to 30°C, and germinants were therefore a crucial supplement to obtain an effect of double heat treatment in this matrix. These data will be valuable when setting up temperature-time-germinant combinations for an optimized spore reduction in mild-heat-treated foods.

Effects of double aging heat treatment on the microstructure, Vickers hardness and elastic modulus of Ti–Nb alloys

Abstract Aging heat treatment can be a good way to optimize mechanical properties, changing the microstructure, and hence, the mechanical behavior of Ti alloys. The effects of aging heat treatments on β-type Ti–30Nb alloy were investigated to evaluate the kinetics of α″ → α + β transformation. The results obtained from differential scanning calorimetry and high-temperature X-ray diffraction experiments indicated the complete decomposition of orthorhombic α″ phase at close to 300 °C, followed by α phase precipitation at 470 °C. The aging heat treatments also enabled us to observe a transformation sequence α″ → β + ω → β + ω + α, indicating martensite decomposition and ω phase precipitation at 260 °C after 2 h, followed by α phase nucleation after heating at 400 °C for 1 h. The elastic modulus and Vickers hardness of Ti–30Nb alloy were found to be very sensitive to the microstructural changes caused by heat treatment.

Crystal Morphology of High-Pressure Crystallized Bisphenol-A Polycarbonate

High-pressure crystallized bisphenol-A polycarbonate (BAPC) samples were investigated using wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The results showed that BAPC chain-extended crystals with c-axis thickness around 2.0 μm were developed through the melt crystallization. Furthermore, a high-crystallinity BAPC sample with a wide variety of microstructures was obtained by a stepwise double-heat treatment at high pressure. In the sample, individual spherulites can be easily exposed and isolated with selective etching, which results in open porous microspheres. These spheres provide the possibility to study the spherulite structure in three dimensions. The open porous microspheres may have functional applications, such as catalyst support and for other surface active materials.

Influence of processing parameters on microstructure and tensile properties of TG6 titanium alloy

Near-isothermal forging of the TG6 titanium alloy was conducted on microprocessor-controlled 630 ton hydraulic press at the deformation temperatures ranging from 850 °C to 1045 °C, the strain rates of 0.0008 s −1, 0.003 s −1 and 0.008 s −1 and the deformation degree from 10% to 70%, and then different double heat treatments were applied to the forged specimens. The microstructural evolutions were researched by optical microscope and the microstructural features, i.e. volume fraction of primary α phase and thickness of lamellar α phase, were measured by means of the image analysis software. The room and high temperature tensile properties were obtained for all the specimens. Effects of microstructure on the properties were analysed by scanning electronic microscope. It was found that tenslie properties depended on microstructural features strongly. The plots of ultimate tensile strength vs. thickness of α lamellae and elongation vs. volume fraction of primary α phase produced straight lines. The liner equations were determined by fitting the experimental date, respectively. Compared to other parameters, heat treatment had more influence on the tensile strength and the tensile plasticity was more sensitive to the forging temperature.

The Microstructural Evolution of Inconel Alloy 740 During Solution Treatment, Aging, and Exposure at 760 °C

In this study, the microstructural evolution of Inconel alloy 740 during solution treatment and aging was characterized using optical and scanning electron microscopy. During double solution heat treatment, carbon is liberated from the dissolution of MC carbides during the first solution treatment at 1150 °C, and fine MC carbides are precipitated on gamma grain boundaries during the second solution treatment at 1120 °C. Due to the concurrent decrease in carbon solubility and the increase in the contribution of grain boundary diffusion at lower temperatures, the MC carbides on the gamma grain boundaries provide a localized carbon reservoir that aids in M23C6 carbide precipitation on gamma grain boundaries during exposure at 760 °C. The γ′ phase, which is the key strengthening phase in alloy 740, is incorporated into the alloy microstructure during aging at 850 °C. The main source of microstructural instability observed during exposure at 760 °C was the coarsening of the γ′ phase.

Microstructure and ionic conductivity of Li 1 + xAl xTi 2 − x(PO 4) 3 NASICON glass-ceramics

Fully crystallized glass-ceramics of the Li 1 + x Al x Ti 2 − x (PO 4) 3 system were obtained by crystallization of a precursor glass, which shows a tendency for homogeneous nucleation. Different microstructures were obtained by single and double stage heat treatments. It is shown that, in the case of a single heat treatment, the ionic conductivity increases by three orders of magnitude when the temperature treatment increases from 700 to 1000 °C, reaching a maximum of 1.3 × 10 − 3 S⋅cm − 1 at room temperature. As deduced from X-ray diffraction, this enhancement in ionic conductivity is related to an increase of the sample's crystallinity. For samples obtained by double stage heat treatments, i.e., a heat treatment to induce nucleation followed by a second one for crystal growth, the ionic conductivity tends to increase when the duration of the nucleation treatment is reduced which leads to an increase in the average grain size of the glass-ceramics.

Controlled crystallization and ionic conductivity of a nanostructured LiAlGePO 4 glass–ceramic

A Li 1.5[Al 0.5Ge 1.5(PO 4) 3] glass composition was subjected to several crystallization treatments to obtain glass–ceramics with controlled microstructures. The glass transition ( T g), crystallization onset ( T x ) and melting ( T m) temperatures of the parent glass were characterized by differential scanning calorimetry (DSC). The glass has a reduced glass transition temperature T gr = T g/ T m = 0.57 indicating the possibility of internal nucleation. This assumption was corroborated by the similar DSC crystallization peaks from monolithic and powder samples. The temperature of the maximum nucleation rate was estimated by DSC. Different microstructures were produced by double heat treatments, in which crystal nucleation was processed at the estimated temperature of maximum nucleation rate for different lengths of time. Crystals were subsequently grown at an intermediate temperature between T g and T x . Single phase glass–ceramics with Nasicon structures and grain sizes ranging from 220 nm to 8 μm were then synthesized and the influence of the microstructure on the electrical conductivity was analysed. The results showed that the larger the average grain size, the higher the electrical conductivity. Controlled glass crystallization allowed for the synthesis of glass–ceramics with fine microstructures and higher electrical conductivity than those of ceramics with the same composition obtained by the classical sintering route and reported in literature.

Genotoxicity of Aqueous Extract From Heated Cooking Oils and its Suppression by Lactobacilli

In the present study the mutagenic and genotoxic effects of aqueous extracts from six cooking oils (extra vergine olive, peanut, sunflower, soybean, corn, and various seeds oils) heated to the respective smoke point were investigated. The Ames test and the SOS Chromotest were carried out for this evaluation. The same oils were also tested after their re-frying, simulating domestic reuse process. Furthermore, the ability of different lactobacilli to reduce the potential genotoxic activity of the fried and re-fried oils was determined applying SOS Chromotest after co-incubation of samples with lactobacilli. The results showed that all the fried oils did not produce mutagenic effects while they induced a SOS response with the highest induction factor for the corn oil. Double heat-treatment caused an increase of the genotoxic activity until two times the first heating. The most susceptible oil to the re-frying procedure was the sunflower oil. The antigenotoxicity results were expressed as percent of genotoxicity inhibition. All the tested strains of lactobacilli exhibited antigenotoxic properties on the fried oils.

Double electrodeposition and heat treatment process for the fabrication of superconducting oxides on the intensified {1 1 3} Ag substrate

The Tl-1223 coated conductor (Tl 0.8Pb 0.2Bi 0.2Sr 1.8Ba 0.2Ca 2.2Cu 3O δ ) was synthesized by using electrodeposition on the intensified {1 1 3} <1 2 1> Ag substrate applying the new method of the repeating electrodeposition/heat treatment. The films were fabricated conducting the first electrodeposition and then heat treatment, after that the second electrodeposition on the first electrodeposition/heat treatment coated conductors. The second electrodeposition on the first electrodeposition/heat treatment/the first electrodeposition/heat treatment coated conductor showed the better quality of the Tl-1223 phases than that of the first electrodeposition/heat treatment coated conductor, showing more compact and dense grains on the films. The thin Tl-1223 films caused by the thinning process were discussed by considering the properties of Tl and the epitaxial growth aspects. The purer Tl-1223 grains obtained at the double electrodeposition/heat treatment are due to the growth from Tl-1223 grains already synthesized during the first electrodeposition/heat treatment, facilitating the epitaxial growth easier than that of the Ag substrate. The second electrodeposition process was successfully performed, obtaining 1.9 × 10 5 A/cm 2 of J c at 0 T at 10 K.

A study on double glow plasma surface metallurgy Mo–Cr high speed steel of carbon steel

Double glow plasma surface metallurgy and heat treatment technology that generated excellent properties reinforcing layer on the surface of Q235 steel was introduced. Using this technology, the alloying elements of Mo, Cr, C can be obtained on the surface of Q235 steel. The content of constituent elements was near or equal to metallurgic high speed steel (HSS). The fundamental principle is that alloying elements Mo, Cr are penetrated into the Q235 steel in a vacuum chamber by glow discharge sputtering so that the content of alloyed layer content was about 20% Mo and 10% Cr on the surface of Q235 steel. Then after ultra-saturated carbonization alloyed constituent was similar to molybdenum HSS with surface carburizing of more than 2.0%. After quenching + low tempering; quenching + cryogenic treatment for 2 h + low tempering; quenching + cryogenic treatment for 16 h + low tempering, it was found that the surface hardness of cryogenic treatment was up to 1600 HV much higher than that without cryogenic treatment. The abrasion test results indicate that carbonization + quenching + low tempering, infiltration of Mo–Cr + carbonization + quenching + infiltration of Mo–Cr + carbonization + quenching + cryogenic processing for 2 h + low tempering and infiltration of Mo–Cr + carbonization + quenching + cryogenic processing for 16 h + low tempering the relative wear resistance was higher by one order in magnitude.

Phenomenon of structural recovery in nonstoichiometric compounds YBa2Cu3O7−δ and EuBa2Cu3O6.8

Experimental results are presented on the phenomenon of recovery (characteristic of aging metallic alloys) in single crystals of nonstoichiometric oxides YBa2Cu3O∼6.6 and EuBa2Cu3O∼6.8. After single low-temperature and high-temperature annealings (200 and 300°C), all signs of spinodal decomposition in these single crystals were found; after double heat treatment (200°C + 300°C), the restoration of structure inherent in the initial state (antiphase domains of twin orientation) occurred.

‘Severe’ wear challenge to ‘as-cast’ and ‘double heat-treated’ large-diameter metal-on-metal hip bearings

The wear generation of double-heat-treated and as-cast large-diameter metal-on-metal (MOM) hip bearings was investigated using standard- and 'severe'-gait simulations. The test hypothesis was that double heat treatment would change MOM hip wear compared with the as-cast condition. Two groups of high-carbon MOM bearings of 40 mm diameter were manufactured and subjected to either hot isostatic pressing (HIP) and solution annealing (SA) or no heat treatment (as cast). The results showed no statistical difference between the two groups under both running-in and steady state conditions. Even under the most 'severe'-gait simulation published to date, the mean volumetric wear rates were 2.9 and 3.9 mm3 per 10(6) cycles for the HIP-SA and as-cast bearings respectively, showing a ten-fold increase in wear compared with walking. These differences were not statistically different; therefore our hypothesis was negated. Changes in alloy microstructure do not appear to influence the wear behaviour of high-carbon cast MOM articulations with similar chemical compositions. This is in sharp contrast with the published significance of bearing diameter and radial clearance on the wear of MOM hip bearings.

The development of monodispersed alumino-chromate spinel nanoparticles in doped cordierite glass, studied by in situ X-ray small and wide angle scattering, and chromium X-ray spectroscopy

The crystallization mechanism in cordierite glass (Mg 2Al 4Si 5O 18) doped with 0.34 mol% Cr 2O 3 has been studied in detail with in situ small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) and ex situ Cr X-ray absorption fine structure (XAFS). The crystalline component comprises an alumino-chromate spinel precipitating within the bulk together with an independent silica-rich stuffed quartz phase that appears to nucleate from the specimen surface. By employing a double heat treatment close to the glass transition, finely dispersed spherical crystallites of a alumino-chromate spinel are grown from Cr nucleating sites. The total crystallized volume of around 4% and the composition of the spinel, MgCr 0.18Al 1.82O 4, are directly related to the Cr content in the starting glass. Moreover, the alumino-chromate particles are found to be closely monodispersed partway through the crystallization process, growing from rough crystallites to smooth particles of radius 210 ± 20 Å, with a final bulk particle density of 1.21 ± 0.4 × 10 15 cm −3. Growth is limited by diffusion in the soft glass and is complete when all the available Cr is exhausted. The advantages of in situ combined scattering, diffraction and spectroscopy for probing the nanostructure, crystallography and local atomic structure in the formation of ceramics, the order in which events take place and the insights this gives in the underlying physical processes are stressed.