Effects of Mg,Fe, Be additions and solution heat treatment on the π-AlMgFeSi iron intermetallic phase in Al–7Si–Mg alloys

The presence of magnesium in Be-free Al–7Si–Mg alloys results in the formation of an undesirable iron-intermetallic known as the π-AlMgFeSi phase. The effect of Mg, Fe, and Be on the formation of this phase in both unmodified and Sr-modified Al–7Si–xMg–yFe alloys containing 0.4–0.8-wt% Mg and 0.1–0.8-wt% Fe has been investigated at a dendrite arm spacing of 65 μm. A qualitative microstructural examination was carried out to study the effect of solution heat treatment (540 °C/8 h) on the decomposition of the π-AlMgFeSi phase (“π-phase”) in Al–7Si–xMg–0.1Fe alloys containing 0.4–1.0-wt% Mg. The results indicate that increasing the Mg and Fe content increases the amount of the π-AlMgFeSi phase formed. Quantitative measurements revealed a reduction in the surface fraction of the π-phase after solution heat treatment. Different levels of decomposition of the π-phase into needles of β-Al₅FeSi iron intermetallic phase (“β-phase”) were observed at 0.4-, 0.6-, and 0.8-wt% Mg, after solution heat treatment.     

Effect of Heat Treatment on the Specific Heat Capacity of Nickel-Based Alloys

Alloy-718 and Udimet alloy 720 are gamma prime strengthened superalloys with excellent mechanical and thermal properties at elevated temperatures, as well as at cryogenic temperatures. The nickel-based alloys were improved to be resistant to creep and become stronger by changing the heat-treatment conditions. The measurement of the specific heat capacity of a nickel-based alloy is a very useful tool to investigate the effect of heat treatment. The specific heat capacity of nickel-based alloys Alloy-718 and Udimet alloy 720 were measured using a differential scanning calorimeter in the temperature range of 100 – 1000 K. The specific heat capacity of the nickel-based alloys increases monotonically with temperature; however, above 800 K, it is strongly dependent on the heat treatment conditions and it is thought to be influenced by the precipitation phase (γ′, γ′′). Optical and scanning electron microscopies are used to investigate the microstructure of the phases. The microstructures of the precipitates are examined.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China.     

Effect of heat treatment in air on the thermal properties of SiC fibre-reinforced composite. Part 1: a barium osumilite (BMAS) matrix glass ceramic composite

The thermal properties have been studied on a glass ceramic composite comprised of a barium osumilite (BMAS) matrix reinforced with SiC (Tyranno) fibres which has been subjected to a heat treatment in air in the range of 700–1,200 °C. Microstructural studies were carried out especially on of the interface between fibre and matrix. The presence of a carbon thin layer in the interface is a typical observation in SiC fibre-reinforced glass ceramic matrix composite systems. The microstructural evaluation and thermal properties showed a degradation of interfacial layer occurred at low heat treatment temperatures, (700–800 °C) this was attributed to the fact that, at those heat treatment temperatures the carbon rich layer formed during processing was oxidised away leaving voids between fibre and matrix, which were linked by isolated silicon-rich bridges. After heat treatment at higher temperatures of 1,000–1,200 °C, the thermal properties were retained or even enhanced by leaving a thick interfacial layer.     

Microstructure, mechanical, and in vitro properties of mica glass-ceramics with varying fluorine content

The design and development of glass ceramic materials provide us the unique opportunity to study the microstructure development with changes in either base glass composition or heat treatment conditions as well as to understand processing-microstructure-property (mechanical/biological) relationship. In the present work, it is demonstrated how various crystal morphology can develop when F⁻ content in base glass (K₂O–B₂O₃–Al₂O₃–SiO₂–MgO–F) is varied in the range of 1.08–3.85% and when all are heat treated at varying temperatures of 1000–1120°C. For some selected heat treatment temperature, the heat treatment time is also varied over 4–24 h. It was established that with increase in fluoride content in the glass composition, the crystal volume fraction of the glass-ceramic decreases. Using 1.08% fluoride, more than 80% crystal volume fraction could be achieved in the K₂O–B₂O₃–Al₂O₃–SiO₂–MgO–F system. It was observed that with lower fluoride content glass-ceramic, if heated at 1040°C for 12 h, an oriented microstructure with ‘envelop like’ crystals can develop. For glass ceramics with higher fluorine content (2.83% or 3.85%), hexagonal-shaped crystals are formed. Importantly, high hardness of around 8 GPa has been measured in glass ceramics with maximum amount of crystals. The three-point flexural strength and elastic modulus of the glass-ceramic (heat treated at 1040°C for 24 h) was 80 MPa and 69 GPa of the sample containing 3.85% fluorine, whereas, similar properties obtained for the sample containing 1.08% F⁻ was 94 MPa and 57 GPa, respectively. Further, in vitro dissolution study of the all three glass-ceramic composition in artificial saliva (AS) revealed that leached fluoride ion concentration was 0.44 ppm, when the samples were immersed in AS for 8 weeks. This was much lower than the WHO recommended safety limits of 1.5 ppm. Among all the investigated glass-ceramic samples, the glass ceramic with 3.85% F⁻ content in base glass (heat treated at 1040°C for 12 h), exhibits the adherence of Ca–P layer, which consists of spherical particles of 2–3 μm. Other ions, such as Mg⁺² and K⁺¹ ion concentrations in the solution were found to be 8 and 315 ppm after 8 weeks of leaching, respectively. The leaching of all metal ions is recorded to decrease with time, probably due to time-dependent kinetic modification of sample surface. Summarizing, the present study illustrates that it is possible to obtain a good combination of crystallization, mechanical and in vitro dissolution properties with the careful selection of base glass composition and heat treatment conditions.     

Inherent frame dependence of thermodynamic fields in a gas

Summary Grad's 13-moment theory – appropriate for rarefied gases – implies that a gas cannot perform a rigid rotation, if it conducts heat. Indeed, stationary heat conduction in a gas between co-axial cylinders at rest in a non-inertial frame exhibits azimuthal components of velocity and heat flux. The fields of velocity and heat flux are calculated. The effects are due to Coriolis terms in all transfer equations that result from the Boltzmann equation.     

On the development of two characteristically different crystal morphology in SiO2–MgO–Al2O3–K2O–B2O3–F glass-ceramic system

The present work demonstrates how crystals with two different characteristic morphologies can be formed in SiO₂–MgO–Al₂O₃–K₂O–B₂O₃–F glass-ceramic system by adopting two sets of heat treatment experiments. In our study, single stage heat treatment experiments were performed at 1,000°C for varying holding time of 8–24 h with 4 h time interval and as a function of temperature in the range of 1,000–1,120°C with 40°C temperature interval. The constant heating rate of 10°C/min was employed for both sets of experiments. The microstructural changes were investigated using Fourier transformed infrared spectroscopy (FT-IR), SEM-EDS and XRD. For temperature variation batches, the microstructure is characterized by interlocked, randomly oriented mica plates (‘house-of-cards’ morphology). An important and new observation of complex crystal morphology is made in the samples heat treated at 1,000°C for varying holding times. Such morphology appears to be the results of composite spherulitic-dendritic like growth of mica rods radiating from a central nucleus. The possible mechanism for such characteristic crystal growth morphology is discussed with reference to a nucleation-growth kinetics based model. The activation energy for crystal nucleation and Avrami index are computed to be 388 kJ/mol and 1.3 respectively, assuming Johnson–Mehl–Avrami model of crystallization. Another important result is that a maximum of around 70% of spherulitic-dendritic like crystal morphology can be obtained after heat treatment at 1,000°C for 24 h, while a lower amount (~58%) of interlocked plate like mica crystals is formed after heat treatment at 1,040°C for 4 h.     

Medical instrument based on a heat pipe for local cavity hypothermia

The design and results of tests of an instrument based on a heat pipe for local cavity hypothermia are presented. The instrument is a part of a device for noninvasive nonmedical treatment of inflammatory diseases of the organs of the small pelvis, pathologies of alimentary canal, etc. Academic Scientific Complex “A. V. Luikov Heat and Mass Transfer Institute, Academy of Sciences of Belarus,” Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 3, pp. 382–385, May–June, 1996.     

Microstructure and phase stability in a Nb–Mo–Cr–Al–Si alloy

The microstructures in as-cast and heat-treated samples of an Nb–27Mo–27Cr–9Al–9Si (in at.%) alloy have been investigated using X-ray diffraction and electron microscopy techniques. The as-cast alloy comprises a dendritic A2 solid solution surrounded by a eutectic mixture of A15 and C14 phases. After heat treatment at 1,000 °C, there is extensive precipitation of A15 and C15 phases within the A2 dendrites, while the A15/C14 eutectic remains essentially unchanged. After heat treatment at 1,500 °C, the precipitates within the A2 phase exhibit the A15 and C14 structures; these are coarser and more equiaxed than those formed at 1,000 °C, and there is also extensive coarsening/spheroidization of the A15/C14 eutectic. Small particles of two unknown phases were also observed within the A2 dendrites in the heat-treated samples. The orientation relationships between the phases have been identified and these are used to deduce the way in which the microstructure develops.     

Plasma nitriding of AISI 52100 ball bearing steel and effect of heat treatment on nitrided layer

In this paper an effort has been made to plasma nitride the ball bearing steel AISI 52100. The difficulty with this specific steel is that its tempering temperature (~170–200°C) is much lower than the standard processing temperature (~460–580°C) needed for the plasma nitriding treatment. To understand the mechanism, effect of heat treatment on the nitrided layer steel is investigated. Experiments are performed on three different types of ball bearing races i.e. annealed, quenched and quench-tempered samples. Different gas compositions and process temperatures are maintained while nitriding these samples. In the quenched and quench-tempered samples, the surface hardness has decreased after plasma nitriding process. Plasma nitriding of annealed sample with argon and nitrogen gas mixture gives higher hardness in comparison to the hydrogen–nitrogen gas mixture. It is reported that the later heat treatment of the plasma nitrided annealed sample has shown improvement in the hardness of this steel. X-ray diffraction analysis shows that the dominant phases in the plasma nitrided annealed sample are ε (Fe_2 − 3N) and γ (Fe₄N), whereas in the plasma nitrided annealed sample with later heat treatment only α-Fe peak occurs.     

Optimization of composition and heat treatment design of Mg–Sn–Zn alloys via the CALPHAD method

This work is focused on the application of the calculation of phase diagrams method for alloy and heat treatment design. We analyzed the influence of Zn content on the precipitation of Mg₂Sn in Mg–Sn–Zn alloys. A comparison with previous studies in the Mg–Sn–Zn system was made according to the published results and computational thermochemistry simulations. The phase evolution in the Mg–Sn–Zn system was evaluated for the different compositions, and the simulations were used for precise alloy and heat treatment design. The composition of the ternary alloy was set as Mg–8wt%Sn–1.25wt%Zn. The Sn and Zn content was designed and confirmed to be within the α-Mg solubility limit at the solution treatment temperature. The addition of Zn and the heat treatment applied resulted in the enhancement and refinement of the Mg₂Sn precipitation. Three Vickers micro-hardness maxima were detected: precipitation of metastable Mg–Zn phases, heterogeneous precipitation of Mg₂Sn on the Mg–Zn precipitates, and Mg₂Sn precipitation in the α-Mg matrix. The CT simulations were found to be a valuable alloy design tool.     

Heat treatment of wollastonite-type Y–Si–Al–O–N glasses

Cumulative work over the last twenty years has defined the glass-forming regions in several M–Si–Al–O–N systems (M = Mg, Ca, Y, Ln) with the resulting crystalline products identified after heat treatment. Glass-forming regions in nitrogen-rich sialon glasses have been recently reported and heat treatment of some of these glasses in the Y–Si–Al–O–N system has been performed. The crystallization of yttrium-containing glasses is particularly sensitive to small variations in composition and heat treatment temperature and in the current work the results of three series are discussed: (1) a single composition, Y15.2Si14.6Al8.7O54.6N6.9 (16 e/oN), treated at 30 °C intervals between 875–1410 °C; (2) compositions of a constant Y: Si:Al ratio of 3:3:2 and up to 32 e/oN and (3) selected compositions lying on the 28 e/o N plane. Two different sets of crystalline products are found to form above and below 1200 °C. This revised version was published online in November 2006 with corrections to the Cover Date.     

Heat transfer and hydraulic resistance in channel cooling systems with a discontinuous wall

The authors give results of measuring the hydraulic resistance, heat transfer, and temperature fields at the numbers Re=70–3·10⁴ and Pr=5.5–8 for cooling systems with rectangular channels with different kinds of discontinuity of their walls involving additional channels that act as intensifiers of heat transfer. The regions of Re numbers in which this intensification is energy-profitable are revealed. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 2, pp. 224–231, March–April, 2000.     

Influence of stefan flow on the characteristics of heterogeneous combustion of a carbon particle in air

The influence of Stefan flow and radiation-induced heat losses on the characteristics of stationary high-and low-temperature stable and critical regimes of heat and mass transfer of a carbon particle in air is analyzed. The investigations are sponsored by the International Fund “Vidrodzhennya” within the framework of the program ISSEP (contract No. K6V100). Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 1, pp. 146–152, January–February, 1997.     

Hemodynamics and heat transfer in controlled whole-body hyperthermia: modeling of processes

The possibilities of describing structural couplings between the organs of a human being subjected to a treatment procedure of controlled whole-body hyperthermia at 43–44°C are considered. The requirements on a model that characterizes changes in the hemodynamics have been formulated, and the interrelations between the models of hemodynamics and heat transfer are shown. As an example of the implementation of the proposed approaches, a system of equations is given that describes heat exchange between an organism and a heat carrier, numerical simulation in the Matlab, toolbox Simulink medium is carried out, and the results of simulation are presented. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 6, pp. 1188–1197, November–December, 2008.     

Investigation of regimes of thermogravitational convection of a fluid between coaxial semicylinders with a heat-conducting shell in the presence of a local energy source

A numerical analysis has been made of the thermodynamic regimes of natural convection of a Newtonian fluid satisfying the Boussinesq approximation in the gap between coaxial semicylinders with finitely-thick walls in the presence of the heat-release source under the conditions of convective heat exchange with the environment. A mathematical model has been formulated in the dimensionless variables current function–velocity vorticity vector–temperature in polar coordinates. Streamlines and velocity and temperature fields reflecting the influence of the Prandtl number Pr = 0.7 and 7.0, the nonstationarity factor 0 < τ ≤ 300, the dimensions of the energy source, and of the relative thermal conductivity on the flow regimes and heat transfer have been obtained.     

High temperature phase stabilized microstructure in Mg–Zn–Sn alloys with Y and Sb additions

Mg–Zn–Sn alloys exhibit poor structural stability at elevated temperatures that restricts utilization of these alloys. Small additions of alloying elements forming high temperature phases (HTP) were used to improve the structural stability of the Mg–Zn–Sn alloy. The main goal of this work was to investigate the microstructure evolution of the Mg–Zn–Sn-alloy with additions of Y and Sb during a wide scope of heat treatments, and to elucidate peculiarities of an HTP-stabilized microstructure. In order to clarify the substructure features and phase precipitation after each step of the heat treatment, XRD, TEM, SEM and EDS analyses were applied. It was found that in the dendrite structure formed during solidification, HTP-particles are concentrated in the inter-dendrite regions. Solution treatment of the as-cast structure at 440 °C for 96 h lead to the formation of α-Mg grains of 50–80 μm in diameter with a characteristic substructure. The presence of HTP-particles prevented dislocation recovery and movement of dislocation walls during solution treatment, and by this way restricted annihilation of grain boundaries between dendrites of close orientation, and lead to the formation of a substructure with sub-grains of 20–30 μm. The sub-grain boundaries are pinned by HTP-particles and are strengthened by the MgZn₂ and Mg₂Sn binary precipitates during aging. Precipitate depleted zones formed near grain- and sub-grain boundaries during aging were bordered by a “crust” of enlarged binary particles. Such pinned sub-grain microstructure provides a high structural stability of the alloys at elevated temperatures.     

Nanorods of silicon carbide from silicon carbide powder by high temperature heat treatment

Nanorods of silicon carbide were found to be produced directly from silicon carbide powder when subjected to high temperature heat treatment. The powder with 20–50 μm grain size was kept in a graphite crucible (enclosed in a chamber/furnace) and heated from its bottom at 2700 °C for 15 min by employing a typical configuration of arc plasma (Ar). The heating was then followed by chamber cooling (up to room temperature) for 2 h. Silicon carbide nanorods of 10–120 nm diameter and 5–20 μm length grew within the powder when the graphite crucible was kept 90% closed at its top end during the heat treatment. The heat treated powder and nanorods were evaluated by XRD, SEM, AFM, HRTEM and micro Raman spectroscopy. A catalyst (Fe) driven two stage VLS mechanism is proposed to understand the growth of the nanorods.     

Tensile properties of a Fe-32Mn-6Si shape memory alloy

The tensile properties of a Fe-32Mn-6Si shape memory alloy were investigated. It was found that tensile properties depend on temperature, heat treatment and material structure. The relationships of martensitic transformation, tensile properties, and shape memory effect are discussed. Finally, we propose a macroscopic one-dimensional constitutive law describing the thermomechanical behavior in tensile loading. Numerically obtained results are close to the experimental ones. __________ Translated from Problemy Prochnosti, No. 2, pp. 55–65, March–April, 2008.     

Characteristic features of the boiling of emulsions having a low-boiling dispersed phase

The results of investigation of heat transfer from thin wires to a boiling emulsion, the dispersed phase of which is formed from a liquid with a boiling temperature much lower than the boiling temperature of the dispersion medium, are presented. Two variants of boiling of such an emulsion are possible: boiling of the dispersed phase alone and simultaneous boiling of the dispersed phase and dispersion medium. In the present work, only the first variant has been studied; it is distinguished by the following most important features: high superheat of the dispersed-phase droplets ΔT_sup of the emulsion and a wide temperature range of bubble boiling (50–200°C). For conventional heat carriers (pure liquids and solutions), the value of ΔT_sup does not exceed 1–10°C, with the bubble-boiling interval lying within the range from 5 to 20°C. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 6, pp. 81–84, November–December, 2006.     

Transformation characteristics of TiNi/TiNi alloys synthesized by explosive welding

Effects of severe deformation and heat treatment on the transformation behaviors of explosively welded duplex TiNi/TiNi shape memory alloys (SMAs) were investigated by the differential scanning calorimeter (DSC). The explosively welded duplex TiNi/TiNi plate of 0.7 mm in thickness was cold-rolled at room temperature to the extent of 60% reduction in thickness and then annealed at different temperatures (573–973 K) for different time (15 min–10 h). Low temperature (623–723 K) heat treatment led to amorphous crystallization. At higher temperature (873 K), the re-crystallization took place in the specimens. Analysis showed that the change of internal stresses is just the root cause of the change of transformation temperature. The relationships between the transformation behaviors and the heat treatment were discussed in the present report.