Preliminary Heat Treatment Research Articles

Effect of heat-treated basalt fibre on the structure of chemisorption composite material made from it

Preliminary heat treatment of basalt fibre used for synthesis of phenol-formaldehyde cation-exchange fibre material increases the activity of the reinforcing system. Better chemisorption properties of cationexchange fibre material (CEFM) made from this fibre are the consequence of heat treatment.

Magnetic properties and hardness of maraging steel 08X15H5Д2T and nondestructive testing of retained austenite in parts

Dependences of the coercive force, saturation magnetization, residual induction, relaxation magnetization and magnetic susceptibility, maximum magnetic permeability and associated magnetic field, electrical resistivity, and hardness of maraging steel 08X15H5Д2T on the conditions of preliminary heat treatments, hardening, and subsequent aging have been studied. The content of rtained austenite in specially prepared specimens was determined. These specimens were subsequently used to calibrate a differential magnetic instrument. Such an instrument is also used to determine the content of retained austenite in aircraft bolts.

Precipitation of Phases in Al-Mg-Si-Cu Alloy with Sc and Zr Additions during Heat Treatment

In the present work the sequence of phases in Al-1%Mg-0.6%Si-1%Cu (in wt %) alloys with 0.4%Sc and 0.2%Zr additions during heat treatment has been studied. The investigated alloys were cast into copper mould to ensure high cooling rate during solidification and the retention of Sc and Zr in the supersaturated solid solution. Two−step preliminary heat treatment was applied: the annealing at temperature 300°C or 350°C followed by quenching from 540°C to water. The precipitation of the Q′ and Al3Sc phases has been observed during the first step of annealing. The annealing at 540°C has led to complete dissolution of the Q′ particles and growth of the spherical particles of the Al3Sc phase. The increase of hardness during subsequent ageing at 165°C (typical ageing temperature of the 6xxx alloys) has been caused by the formation of needle-like Q′ phase which coexist with Al3Sc precipitates.

Electrospark powders of shape memory alloys

Powders of Ti-Ni and Ni-Mn-Ga alloys are obtained by the electrospark method. It is established that the largest particles are of irregular shape and the smaller ones are spherical. Some spherical particles are hollow. No carbon contamination is found within the Ti-Ni and Ni-Mn-Ga powders obtained in cryogen liquids. The Ti-Ni powders of all compositions are mixtures of austenite and martensite phases. Preliminary heat treatment of spherical-particle Ni-Mn-Ga alloys is needed to activate their martensitic transformation. The martensitic transformation proceeds over quite a wide temperature range, which is indicative of high dispersion, and the martensitic temperatures increase, which is indicative of a minor difference between the chemical compositions of powders and massive samples.

Dislocation-related luminescence in silicon, caused by implantation of oxygen ions and subsequent annealing

Multiple implantation of oxygen ions with energies of 0.1–1.5 MeV at doses of 7 × 1013−2 × 1014 cm−2 and subsequent annealing in a chlorine-containing atmosphere at 900°C for 4 h give rise to dislocation-related luminescence in p-Si. A p → n conductivity-type conversion is also observed in this case in the surface layer of Si, which indicates that electrically active donor centers are formed in the process. Preliminary heat treatment of wafers covered with an erbium-doped film of tetraethoxysilane (TEOS) in argon at 1250°C for 1 h does not preclude the appearance of dislocation-related luminescence, but affects the parameters of the dislocation-related lines (peak positions and intensities).

Electronic states spectroscopy of Hydroxyapatite ceramics

Photoluminescence, surface photovoltage spectroscopy and high-resolution characterization methods (Atomic Force Microscopy, Scanning Electron Microscopy, X-ray spectroscopy and DC conductivity) are applied to nanostructured Hydroxyapatite (HAp) bioceramics and allowed to study electron (hole) energy states spectra of the HAp and distinguish bulk and surface localized levels. The measured trap spectra show strong sensitivity to preliminary heat treatment of the ceramics. It is assumed that found deep electron (hole) charged states are responsible for high bioactivity of the HAp nanoceramics.

Deformation of unfired phosphate-bound refractories. Part 3. Deformation of hardened cements on heating and cooling

Deformation tests have been made on hardened cements. A difference from unhardened ones, which show considerable plastic (viscous) deformation, is that the hardened ones show mainly elastic strain with a small inelastic component at a temperature exceeding the preliminary heat treatment value.

Fatty acid esters of 3-chloropropane-1,2-diol in edible oils

A series of 25 virgin and refined edible oils, obtained from retailers, was analyzed for levels of free 3-chloropropane-1,2-diol (3-MCPD) and 3-MCPD released from esters with higher fatty acids (bound 3-MCPD). Oils containing free 3-MCPD ranging from <3 µg kg−1 (LOD) to 24 µg kg−1. Surprisingly, bound 3-MCPD levels were much higher and varied between <100 (LOD) and 2462 µg kg−1. On average, virgin oils had relatively low levels of bound 3-MCPD, ranging from <100 (LOD) to <300 µg kg−1 (LOQ). Higher levels of bound 3-MCPD were found in oils from roasted oilseeds (337 µg kg−1) and in the majority of refined oils (<300–2462 µg kg−1), including refined olive oils. In general, it appears that the formation of bound 3-MCPD in oils is linked to preliminary heat treatment of oilseeds and to the process of oil refining. Analysis of unrefined, de-gummed, bleached, and deodorized rapeseed oil showed that the level of bound MCPD decreased during the refining process. However, additional heating of seed oils for 30 min at temperatures ranging from 100 to 280°C, and heating at 230°C (260°C) for up to 8 h, led to an increase in bound 3-MCPD levels. On the other hand, heating of olive oil resulted in a decrease in bound 3-MCPD levels. For comparison, fat isolated from salami was analyzed for intact fatty acid esters of 3-MCPD. This fat contained bound 3-MCPD at a level of 1670 µg kg−1 and the fatty acid esters of 3-MCPD mainly consisted of 3-MCPD diesters; monoesters of 3-MCPD were present in smaller amounts. The major types of 3-MCPD diesters (about 85%) were mixed diesters of palmitic acid with C18 fatty acids (stearic, oleic, linoleic acids). These diesters were followed by 3-MCPD distearate (11%) and 3-MCPD dipalmitate (4%). Generally, very little 3-MCPD existed as the free compound (31 µg kg−1).

Direct and reverse elastic aftereffects of spring ribbon from nitrogen-bearing steel Kh21G10N7MBF

Direct and reverse elastic aftereffects in corrosion-resistant nitrogen-bearing steel Kh21G10N7MBF (0.5% N) are considered depending on the preliminary heat treatment (quenching + deformation + aging) and on the temperature and time conditions of the occurrence of the direct and reverse elastic aftereffects.

Influence of fullerene on the rheological characteristics of melts of the polyamide composite forming the structure of a semi-interpenetrative polymer mesh

The time change in the melt viscosity of the polyamide composite forming at the final stage a polymer with the structure of a semi-interpenetrative polymer mesh has been investigated. To impregnate with the composite melt the carbon fiber for forming carbon-filled plastics, it is necessary to preserve the low viscosity of the melt for a long time. This is achieved by preliminary heat treatment of the composite and introduction of fullerene into it.

Thermal Expansion of BaO · 2B2O3 in the Vitreous and Crystalline States: II. Thermal Expansion of Polycrystalline Barium Diborate Prepared by Crystallization of Glass Powder of the Same Composition

The thermal expansion of polycrystalline barium diborate prepared by crystallization of the glass powder of the same composition is investigated. It is revealed that the dilatometric parameters are characterized by a hysteresis, which manifests itself in a substantial difference between the dilatometric curves upon heating and cooling. The hysteresis characteristics depend on the temperature of preliminary heat treatment during crystallization, the temperature range of measurements, and the direction of the temperature change in the course of dilatometric experiments. It is assumed that transformations of structural modifications occur in the low- and high-temperature ranges and that the quantitative ratio between the modifications in these ranges depends on the temperature.

Effect of Preliminary Heat Treatment on the Stability of Austenite in Steel 08Kh15N5D2T

The effect of the heating rate and long-term holds in the temperature range of inverse martensitic (α → γ) transformation on the stability of austenite in the cooling of chromium-nickel steel 08Kh15N5D2T is studied. Additional conditions for growth of stable austenite in the structure of the steel (to 60%) are determined. Isothermal diagrams of decomposition of retained austenite at negative temperatures after annealing in the (α + γ) range in different modes are plotted.

Effect of Al 3Sc precipitate on the microstructural evolution during accumulative roll bonding in Al–0.2 wt.% Sc alloy

The cold-rolled Al–0.2 wt.% Sc alloy sheets were conducted the following two preliminary heat treatments: (1) as solution treatment at 630 °C for 1 h, and (2) as artificial aging at 300 °C for 5 h. The accumulative roll bonding (ARB) was followed up to eight cycles at ambient temperature. The stored energy release caused by annihilation of dislocation and recrystallization in aged alloy was higher than that in solution treated one in the 2-cycle sample, and this aspect was reversed with increasing cycles. The fraction of high-angle grain boundaries (HAGBs) in both alloys was increased gradually with increasing equivalent strain. However, the alloy of aged and ARBed had relatively higher fraction of HAGBs than the alloy of solution treated and ARBed at the same strain level. The former formed lamellar structure faster than the latter. This variation can attribute to the fact that the nanosized and semi-coherent Al 3Sc precipitates hinder the migration of boundaries and dislocations. However, those precipitates cannot generate the sufficient pinning effect because the driving pressure for recrystallization surpasses the Zener pinning pressure.

Experimental study of titanium/aluminium deposits produced by cold gas dynamic spray

Results of optical microscopy, scanning electron microscopy, X-ray diffraction, porosity and microhardness tests are presented for co-deposited titanium/aluminium materials produced by cold gas dynamic spraying. Cold gas dynamic spray (CGDS) is a rapidly developing coating technology, in which spray particles are deposited through plastic impact on a substrate at velocities of up to 700 m/s and virtually at room temperature. In these experiments, the process produced a reasonably dense material that is a mixture of aluminium and titanium regions, which because of the low temperatures involved have not alloyed together. This paper reports the effect of deposition parameters on the structures formed. In addition, preliminary heat treatment of these titanium/aluminium deposits has shown that they can be readily converted into intermetallic materials.

Zinc nonstoichiometry in ZnO

Excess Zn in powder and in ceramic ZnO is investigated by the atomic absorption photometry (AAP) method. All the ZnO samples tested were previously heat treated at temperature 900 °C and at fixed Zn pressures from 0.1 to 0.6 of saturated p Zn at given treatment temperature. The vapour–crystal equilibrium in ZnO:Zn crystal was established in 20–40 min. To determine the excess zinc in ZnO samples, the AAP of zinc vapour was used in the conditions of solid–vapour equilibrium. Optical absorbance of zinc, proportional to the concentration of zinc atoms in the vapour phase, was registered photoelectrically on the Zn resonance line. The analysis of temperature dependence of zinc pressure indicated that the value of zinc excess lies in the concentration interval of 10 18–10 19 cm −3 and depends on the sample biography and the conditions of preliminary heat treatment. Zn adsorption on powder ZnO grain surfaces and the reactions of impurity metals with excess Zn in ZnO ceramics were observed in Zn AAP experiments.

Excess Zn in ZnO

Excess Zn in ZnO was experimentally investigated. The ZnO samples tested were prepared by heat treatment of ZnO powder or polycrystalline ceramics at a temperature of 900 °C and at fixed Zn pressures from 0.2 to 0.6 of saturated Zn vapour pressure at a given temperature. To determine the excess Zn, atomic absorption photometry of Zn vapour was used under conditions of solid–vapour equilibrium. The optical absorbance, proportional to the concentration of Zn atoms in the vapour phase, was registered photoelectrically on the Zn resonance line. During the atomic absorption photometry measurements all excess Zn was extracted from the solid state into the vapour phase. The analysis of the temperature dependence of Zn pressure indicated that the value of Zn excess lies in the concentration interval of 1018–1019 cm−3 and depends on the sample history and the conditions of preliminary heat treatment. The experimental results were used for preliminary estimation of high-temperature defect equilibrium in ZnO. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Initial Microstructure of Tool Steels on the Thickness and Hardness of Layers Obtained by Nitrocarburizing

The effect of preliminary heat treatment on the microstructure and kinetics of formation of the hardened layer in the process of subsequent nitrocarburizing of steels A681 (ASTM), Kh12M (GOST), Kh12FS (GOST), 6437E (AMS), and X46Cr13 (BS) is studied. Preliminary treatment of two kinds, i.e., annealing and quenching with tempering, is considered. The thermochemical processes are performed in a solid carburizer (powder) at 500°C for 4 h. The thickness, hardness, microstructure, and phase composition of the resulting layers are determined.

Athermal stabilization of Cu–Al–Be β1′ martensite due to plastic deformation and heat treatment

Effects of plastic prestrain and of different heat treatments on the stabilization of martensiticcrystals of a Cu-Al-Be alloy have been studied. Directly quenched and plastically prestrained samples (subjected to preliminary heat treatments, suppressing the stabilization) under go the reverse martensitic transformation in two distinct stages. The first stage is a partial bulk transformation which exhibits typical stabilizatio n properties: shift and broadening of the reverse transformation range. The rest of the martensite is hyperstabilized both in prestrained and quenched samples and retransforms through renucleation of lamellar -phase at temperatures approximately 300 K above the nominal reverse transformation. In prestrained samples, the magnitude of shift and broadening of the first stage of the reverse transformation depends on the degree of plastic prestrain, whereas the renucleation of -phase occurs at nearly constant temperatures, independent of the amount of prestrain. Relative fractions of martensite retransformed to the -phase through the normal mechanism of reverse motion of variant interfaces and through renucleation of -phase depend on the degree of prestrain. Stabilization registered after different heat treatments is virtually instantaneous and it is not related to martensite aging. The conclusion is drawn that heat treatment-induced stabilization in Cu-Al-Bemartensite is athermal, not related to diffusion-controlled processes during aging of martensite, but associated with jamming the motion of interfaces, similar to prestrain-induced stabilization. Plausible mechanisms of athermal stabilization registered after heat treatment are discussed. © 2004 Elsevier B.V. All rights reserved.

New Ideas on the Mechanism of Structure Formation in Nitrided Steels

The main laws of formation of structure and properties of nitrided structural steels are studied depending on their composition, parameters of preliminary heat treatment, and nitriding modes. New factors controlling the structure and operational properties based on new concepts of the mechanism of formation of nitride particles in the nitriding process are determined.

Production of yeast biomass using waste Chinese cabbage

The possibility of using waste Chinese cabbage as a substrate for microbial biomass production was investigated. Cell mass and the protein content of four species of yeast, Candida utilis, Pichia stipitis, Kluyveromyces marxianus, and Saccharomyces cerevisiae, were determined when cultured in juice extracted from cabbage waste. Compared to YM broth containing the same level of sugar, all the strains except C. utilis showed higher total protein production in cabbage juice medium (CJM). Cell mass production was lower for all four strains in heat-treated CJM than in membrane-filtered medium, and this adverse effect was pronounced when the CJM was autoclaved at 121°C for 15min. As a source of inorganic nitrogen, only ammonium sulfate added at a concentration of 0.5g nitrogen per liter of CJM increased cell growth. Of the seven organic nitrogen sources tested, only corn steep powder was effective in increasing cell mass (by about 11%). As a micronutrient, the addition of 0.5mM zinc increased cell mass. The results suggest that juice from waste Chinese cabbages can be used to produce microbial biomass protein without substantial modification, after preliminary heat treatment at temperatures below those required for sterilization.