Effect Of Thermochemical Treatment Research Articles

Effect of thermochemical treatments on laser-induced luminescence spectra from strontium titanate: comparison with swift ion-beam irradiation experiments

Results recently reported on the effect of thermochemical treatments on the (He-Cd) laser-excited emission spectra of strontium titanate (STO) are re-analyzed here and compared with results obtained under ion-beam irradiation. Contributing bands centered at 2.4 eV and 2.8 eV, which appear under laser excitation, present intensities dependent upon previous thermal treatments in oxidizing (O2) or reducing atmosphere (H2). As a key result, the emission band centered at 2.8 eV is clearly enhanced in samples exposed to a reducing atmosphere. From a comparison with the ionoluminescence data, it is concluded that the laser-excited experiments can be rationalized within a framework developed from ion-beam excitation studies. In particular, the band at 2.8 eV, sometimes attributed to oxygen vacancies, behaves as expected for optical transitions from conduction-band (CB) states to the ground state level of the self-trapped exciton center. The band at 2.0 eV reported in ion-beam irradiated STO, and attributed to oxygen vacancies, is not observed in laser-excited crystals. As a consequence of our analysis, a consistent scheme of electronic energy levels and optical transitions can now be reliably offered for strontium titanate.Graphical abstract

Effect of thermochemical treatments on the surface hardening of a circular saw blade: A microstructure comparison of nitride layers, boride layers and TiN coating formed on ASTM A1011 steel

Effect of thermochemical treatments on the surface hardening of a circular saw blade: A microstructure comparison of nitride layers, boride layers and TiN coating formed on ASTM A1011 steel - Volume 27 Issue S1

Study into the effect of thermochemical treatment on VK6 and VK15 hard alloy performance

Study into the effect of thermochemical treatment on VK6 and VK15 hard alloy performance

Effect of thermochemical treatment on the state of SWNT and on the electrical conductivity of epoxy-SWNT composites

An experimental study of single-walled carbon nanotubes (SWNTs) subjected to liquid-phase oxidation with various acid solutions was carried out. The changes in the structure of SWNTs were estimated by the methods of Raman spectroscopy and X-ray structural analysis. Visible decrease of the oriented phase was revealed in the process of liquid-phase oxidation of the samples (the I G/I D-ratio decreases). It was shown that acid treatment leaded to the reduction of the alpha-iron and iron-carbide impurities content in the samples. Composites based on epoxy resin doped by oxidized SWNTs were prepared. Electric conductivity of the composites within SWNT-concentration range from 0 to 1% wt was measured for all used oxidants. It was found that the composites with SWNTs oxidized by mixtures with a predominance of hydrochloric acid have a twice the electric conductivity as compared to composites with untreated SWNTs.

Fatigue behaviour of gear teeth made of case hardened steel: from competing mechanisms to lifetime variability

Jet engines gears are generally made of steel and are case-strengthened via thermochemical treatments such as carburizing or ni-triding causing microstructural modifications, superficial hardening and compressive residual stresses in the surface layers. These treatments increase the resistance to cyclic loads caused by contact between teeth and by the bending loads applied to the teeth. These two loading modes create high stress gradients at the surface. A large number of studies concerning the effect of thermochemical treatments on fatigue resistance have been carried out for uniaxial loads (rotating bending, tension or plane bending). Most of them were undertaken using smooth specimens, which do not correctly reproduce the stress gradient at the root of the gear teeth. A strong dependence between the loading mode and the position of the crack initiation site is also observed. The present work aims at experimentally investigating the fatigue behaviour of case hardened steel with a special focus on crack initiation and growth mechanisms. A vast experimental campaign composed of two parts is undertaken. Firstly, a Single Tooth Bending Fatigue (STBF) test is carried out on gears made of 16NiCrMo13 carburized steel. The resulting Wühler diagram shows high scatter at certain stress levels which suggests a bi-modal behaviour, characterized by very different crack initiation kinetics. Secondly, fatigue tests conducted on notched specimens loaded in plane bending, designed to accurately reproduce the stress gradient observed at the gear tooth root are carried out to confirm this bimodal behaviour and to characterize the failure mechanisms.

Effect of Thermochemical Treatment on the Structure and Mechanical Properties of Materials Based on Aluminum Oxide

According to the standard process, normal electrocorundum is heat treated at 700°C in a rotating drum followed by air cooling. Such heat treatment increases the strength characteristics of abrasive grain. When abrasive paper made from grains with reduced brittleness is working, the effect of reducing the cutting ability due to damage and failure of the cutting surfaces is observed. An increase in the performance characteristics of the abrasive paper was studied by improving the self-sharpening of the grain. Improvement of this performance is achieved by thermochemical treatment in a regulated gas atmosphere and cooling according to a special schedule. Normal electrocorundum during heat treatment in an oxidizing atmosphere changes the structural characteristics due to the decomposition of a solid solution of Ti2O3 in α-Al2O3 by oxidation to TiO2. The formation of a block grain structure with microcracks increases the probability of chipping during the grinding tool operation and the appearance of new cutting surfaces.

Effect of thermo-chemical treatment on tribological features on crankshaft journals of combustion engines

The article presents research on the wear between the bearing and journal surfaces. The investigation was done for two types of layers obtained by: laser drilling of EN-GJS-600 ductile cast iron and gas nitriding of 38 HMJ steel. Wear rates were defined on the base of comparison of surface layer profiles before and after the wear test. Comparing test results it was found that the biggest differences of the surface roughness parameter were obtained for gas nitrided specimens (ε + γ`+ α) while the smallest differences for the laser drilled ones. Moreover the surface layer of specimens was evaluated with the usage of microhardness measurements. The surface of the drilled specimens was characterized with the constant value for the melt layer. At the end of the paper findings of the research were summarized and the conclusions were drawn.

The Effect of Thermo-Chemical Treatment on the Water Resistance of Defatted Soybean Flour-Based Wood Adhesive.

The aim of this study was to effectively improve the water resistance of a defatted soybean flour (DSF)-based adhesive by subjecting DSF to thermo-chemical treatment in the presence of sodium dodecyl sulfate (SDS), and then the crosslinking with epichlorohydrin-modified polyamide (EMPA). The effect of thermo-chemical treatment on the structures and properties of the DSF and DSF-based adhesive were investigated by plywood evaluation, boiling-water-insoluble content, and acetaldehyde value measurements, as well as FTIR, X-ray photoelectron spectroscopic (XPS), X-ray diffraction spectroscopy (XRD), thermogravimetric analysis (TGA), and rheology analyses. The test results revealed that the water resistance of the DSF-based adhesive was significantly improved, attributed to the formation of a solid three-dimensional crosslinked network structure resulted from the repolymerization of DSF, the Maillard reaction between the protein and carbohydrate, and chemical crosslinking between the crosslinker and DSF. Moreover, SDS destroyed the hydrophobic interactions within protein and inhibited macromolecular aggregations during the thermal treatment. Therefore, more reactive groups buried within the globular structure of the soybean protein component of DSF could be released, which supported the repolymerization, Maillard reaction, and chemical crosslinking of DSF, thereby leading to an improved crosslinking density of the cured DSF-based adhesive. In addition, the adhesive composed of thermo-chemically treated DSF and EMPA exhibited preferable viscosity and viscosity stability suitable for the production of wood composites.

WEAR RESISTANCE OF STRUCTURAL STEELS AS A RESULT OF BORONISING OPERATIONS

This paper presents the results of investigations on the effect of thermochemical treatment, boronising and chemical composition of selected structural steels on their wear in sliding friction process. The operation of boronising on C45, 37CrNiMo, 42CrMo6, 41Cr4, 50CrSi4-4 steels was performed by powder method at 950°C for 8 h. Following this operation, rod sections of the test steels were subjected to quench hardening from 850°C with isothermal holding at 300°C for 1h. The assessment of the construction, thickness and microhardness of boronised layers depending on the level of carbon and alloying elements in chemical composition of analysed steels was made. The testing for wear resistance of steels after boronising was carried out with the sliding friction method by applying a load of 150 N, counter-sample rotational speed of 1000 rpm and using aqueous solution of potassium chromate as a cooling medium. The metallographic observations of the structure and thickness measurement of the boronised layers were carried out using a light microscope, while the identification of phases was made by the X-ray qualitative analysis method. The hardness and microhardness measurements were taken by the Vickers method.

Effect of Novel Thermo-Chemical Treatment on Bending Strength of Laminated Glass

The science of thermal and chemical treatment of glass is well documented. The Laminated Glass (LG) is usually not treated as either treated glass is used during production or lower melting temperature of interlayer does not allow the treatment. The present work reports the novel methods of thermo-chemical treatment of LG having annealed soda lime glass plies. Five thermo-chemical treatments were performed on LG using different salts (Potassium Nitrate Carbohydrazide, Lithium Nitride), via clay coating (saturated with salts), using fused silica wafer coated with a thin graphene layer and utilizing the microwave heating. The bending strength is measured before and after thermo-chemical treatment using Q-set coupled bending tester (following the ASTM D790-03). The linear elastic model is utilized for obtaining normal stress and deformation at fracture load using ANSYS 14.5. The bending strength of thermo-chemical treated LG sample was found significantly higher than untreated LG in the most cases. The fracture pattern of the treated LG was also modified compared to the untreated LG as impurities and defects were reduced during treatment. The mechanics of increased bending strength and modified fracture is also discussed with reference to the effects of thermo-chemical treatment of LG, however, the need of a specialized numerical method that can effectively model the implications of treatment on LG and multiple fractures experienced by the LG during testing are suggested as future work.

Effect of Thermochemical Treatment in Regulated Gas Media on the Thermal Resistance of Zr1%Nb Alloy

We perform experimental investigation of the oxidation of Zr1%Nb zirconium alloy after preliminary thermochemical treatment of ring specimens made of the pipe of a fuel element. It is shown that the preliminary nitriding protects Zr1%Nb alloy against the oxidation in air (T = 550°C, τ = 100 h) to a greater extent than the preliminary treatment in regulated oxygen-containing media.

Effect of thermochemical treatment on conductivity and mechanism of current flow in MK-40 sulfocationite membrane

The effect of thermal treatment on the conductivity, diffusion permeability, and structure of MK-40 sulfocationite membrane is studied in the neutral, alkaline, and acidic media. Based on the experimental concentration dependences of membrane conductivity, within the extended three-wire model of conduction, the fractions of current passing through different conduction channels of membrane and the structural parameters, which characterize the volume fractions of conducting phases and their mutual orientation against the electric current, are calculated. It is found that the thermal treatment changes the mechanism of current flow in the membrane due to the reorganization of transport channels structure leading to a considerable increase in the moisture content due to an increase in the polymer macroporosity. The information on the variation of structure of transport channels in the membrane after the thermochemical treatment was obtained by the analysis of model parameters and supported by the data of independent study of its diffusion permeability and the morphology of surface and cross-section of swollen samples by the method of scanning electron microscopy.

Effect of thermochemical treatment on the surface morphology and hydrophobicity of heterogeneous ion-exchange membranes

A comparative analysis is performed on the effect thermochemical treatment in aqueous, alkali, and acid media has on the surface morphology and hydrophobicity of swelling heterogeneous ion-exchanged membranes. A correlation between changes in surface morphology and hydrophobicity is established. It is shown that under prolonged (50 h) membrane thermal treatment above room temperature, hydrophobicity is reduced due to substantial enlargement of cavities and cracks resulting from the partial destruction of inert binder (polyethylene) and reinforcing poly-ɛ-caproamide fabric (capron).

Effect of thermochemical treatment on the structure of inulin and its gelling properties

SummaryThe aim of this study was to investigate rheological properties of inulin gels and the changes in the inulin structure after heating the high polymerised inulin (DP ≥ 23) solutions at different pH. The 20% inulin solutions were heated at pH 3, 5 and 7 at 60 and 80 °C followed by 21 h storage at 5 and 25 °C. Rheological properties evaluation indicated that the increase in the heating time and temperature significantly (P ≤ 0.05) influenced on the inulin structure. Reducing sugars, cryoscopy and HPLC analysis revealed that chemical structure of inulin is stable in neutral and slightly acidic conditions (pH 5). Gelation of the high polymerised inulin solution after heating at pH 7 and 80 °C could be inhibited after dissolving the inulin crystallites which act like seeding crystals. At lower temperatures in which, not all crystallites were dissolved; it was feasible for the solutions to form firm inulin gels.

Effect of thermo-chemical treatments on the luminescence and scintillation properties of CaWO4

In this work, we investigated the influence of thermal annealing in different atmospheres on the luminescence and scintillation properties of CaWO4. Luminescence and luminescence excitation spectra were examined using VUV synchrotron radiation. Thermal treatment causes change of the defect subsystem of the crystal, resulting in the alteration of the spectral dependences. The most obvious effect is the relative change in the intensity of the defect emission band which is excited below the fundamental absorption edge 4.7eV. Studies of the scintillation kinetics and light yield carried out over a temperature range 8–300K showed that former does not change upon the treatment, in contrast to the intensity of scintillations. It is found that ∼50% increase of the scintillation response can be achieved for CaWO4 samples annealed in hydrochloric acid.

Effect of thermo-chemical treatment on magnetic and spin-transport properties of epitaxial Fe3O4 (1 0 0)/MgO films

The effect of thermo-chemical treatment on the magnetic and spin-transport properties of epitaxial Fe3O4 (100) thin films grown on MgO (100) substrates was investigated. We found that the magnetization of the films remarkably increases after just 4min of annealing in air at 250°C. In situ resistance measurements were carried out during the treatment and the contribution of domains and antiphase boundaries on the change in resistance was clarified. A model involving a change in the antiferromagnetic coupling at the antiphase boundaries during the treatment is proposed.

The effect of thermochemical treatments on case properties and impact behaviour of Astaloy CrM

Ion nitriding, ion nitrocarburizing, and gas nitrocarburizing were carried out on Astaloy CrM samples at a range of conditions. The influence of each treatment on case properties (including the composition of compound layer, hardness profile, and microstructure) and impact energy were investigated. Characterisation was performed by microhardness measurement, optical and scanning electron microscopy, and X-ray diffraction. XRD analysis indicated that the compound layers produced by different processes included ɛ and γ′ phases. In ion nitriding, the amount of ɛ phase, maximum microhardness, and the depth of diffusion zone increased with the nitrogen content of the atmosphere. Compared with ion nitriding, both nitrocarburizing processes showed lower maximum microhardness and thicker diffusion zone. All treatments reduced the impact energy of the samples; however, the effect of gas nitrocarburizing was more pronounced. Fractography observations confirmed that for ion-treated samples, cleavage was the prominent morphology from surface to a limited depth. Meanwhile, for gas-nitrocarburized sample, cleavage morphology was extended from the surface to a deeper distance.

Enhancement of the magnetization saturation in magnetite (100) epitaxial films by thermo-chemical treatment

The effect of thermo-chemical treatment on the ease of saturation in a magnetic field of epitaxial magnetite (100) thin films grown on MgO (100) substrates was investigated. It was found that the films maintained a fully strained state with the MgO substrate during the treatment in air. No other iron oxide phase apart from the magnetite was observed in the treated film. Yet, remarkably the treated films showed a higher magnetization compared to that of original ones. A model involving a change in antiferromagnetic coupling at the antiphase boundaries during the treatment is proposed.

The effect of thermochemical treatment on the structure and hardness of electroless Ni–P coated low alloy steel

In the present research, three groups of the low alloy steel samples include bare steel, thermochemical treated steel and electroless Ni–P coated steel followed by thermochemical treatment were prepared. Surface characterizations such as morphology, present phases, roughness and hardness were evaluated by SEM, EDS, XRD, profilometry and microhardness tests. It is found that the effect of the thermochemical treatment in H 2/NH 3 mixture on coated samples dependent on the coatings thickness is different. In addition, it is shown that a multicomponent coating containing phosphide, nitride and intermetallic phases as well as diffusion region can be developed in the thin electroless Ni–P coated steel by thermochemical treatment.

Effect of Thermochemical Treatment of Anthracite on Its Activation by Steam

The effect of thermochemical treatment of anthracite, including its oxidation, impregnation with a solution of a compound of an alkali metal, and heat treatment in an inert gas atmosphere on the subsequent activation of the material with steam was studied. It was shown that such treatment of anthracite leads to considerable improvement at the final stage of the production of active carbon; there is an increase (of almost three times) in the rate of activation (burn off) of the anthracite and better pore formation compared with the technology involving direct activation with steam.