High Temperature Interval Research Articles

Heat pipe-enhanced two-stage thermoelectric harvester based on phase change material

The thermoelectric generator (TEG) technology is important for improving energy efficiency. However, the TEG limited by poor thermoelectric material properties and thermal transfer strategies faces challenges in achieving excellent heat harvesting capacity, especially for large-temperature gradients. Herein, we reported a heat pipe-enhanced two-stage thermoelectric generator (HTTEG) enabled by bismuth alloy-based PCM for effective space waste thermal harvesting. We comprehensively explored the effects of different thermal-enhanced strategies on HTTEG performance. Compared with copper plate and horizontal layout, the effective thermal conductivity obtained by vertical-planar heat pipe is 1.1 × 104 W/mK enhanced by 79.2 and 33.0 times, which has outstanding advantages in achieving considerable temperature difference and excellent thermoelectric harvesting capacity of the HTTEG. We also systematically discussed the thermoelectric properties of heat pipe-enhanced one-stage TEG (HOTEG) and HTTEG by simulation and LED test bench. The results show that the bismuth alloy-based PCM with considerable latent thermal capacity and remarkable heat transfer characteristics can suppress temperature fluctuations and expand thermoelectric harvest interval, achieving excellent power output capacity. Compared with the HOTEG, the thermoelectric power achieved by HTTEG is 4.45 W enhanced by 581.8 %, because optimizing the spatial layout of stage-two thermoelectric modules to the high-temperature gradient interval achieves remarkable heat harvesting efficiency.

Rheological Behavior of a New Amorphous Alloy (Al74Cu16Mg10)99,7Zr0.3

A new amorphous alloy (Al74Cu16Mg10)99,7Zr0.3 was prepared the applying a melt-spinning technique. Temperature dependence of viscosity of the alloy was determined using data from a PerkinElmer TMS2 thermo-mechanical analyzer processed according to a methodology based on the Free Volume Model (FVM). The strength of the alloy was calculated according to the Yang equation and the glass-forming ability was calculated according to the values of the Angell index mA. The activation energy of crystallization and the activation energy of the glass transition were computed using data from differential scanning calorimetry and thermomechanical experiments respectively. The activation energy of crystallization Еx = 168 ± 3.7 kJ/mol, was found to be higher than the activation energy of the glass transition Еg = 156 ± 1.4 kJ/mol, which means a dominant contribution of the atomic transport barrier, compared to the nucleation barrier. The relatively high temperature interval of the supercooled melt state Tx-Tg = 32 K and the low viscosity values in the same range ƞ(Тg) = 3.40E + 11 Pa.s and ƞ(Тx) = 1.87E + 10 Pa.s would allow thermomechanical treatment of the alloy in the temperature range of supercooled melt.

Performance characterization and microscopic properties of asphalt modified with rapeseed heavy oil-activated waste rubber powder

To improve the waste rubber powder modified asphalt viscosity is high, poor storage stability, and other shortcomings, 40 mesh, 60 mesh, and 80 mesh are three kinds of mesh rubber powder using rapeseed heavy oil pre-swelling activation way to prepare modified asphalt, improve the waste rubber powder modified asphalt storage stability and reduce the viscosity. The optimum blending amount of rapeseed heavy oil-activated waste rubber powder was determined by setting three oil-rubber ratios, and the unactivated waste gum powder modified asphalt was set as a control group, and the physical, rheological, and microscopic properties of the asphalt were evaluated accordingly. The optimum preparation parameters under the premise of setting the total dosage of modifier as 20% were: the mass ratio of rubber powder to rapeseed oil was 2:1, and the mesh size of rubber powder was 80 mesh. Rapeseed heavy oil-activated waste rubber powder modified asphalt storage stability and low-temperature performance improved, viscosity decreased, but high-temperature performance decreased at the same time. Compared with the unactivated waste rubber powder modified asphalt, the softening point decreased by an average of 16%, the needle penetration increased by an average of 19%, the ductility increased by an average of 44%, the viscosity decreased by an average of 22%, and the softening point difference decreased by an average of 44%. In the high-temperature rheological performance test set temperature interval, the rutting coefficient G*/sinδ decline, creep stiffness Ѕ, and creep rate m have increased. Therefore, rapeseed heavy oil activation can effectively improve the overall stability of waste rubber powder-modified asphalt and can reduce the overall viscosity, which is conducive to the uniform dispersion of rubber powder in asphalt.

Investigation on effects of thermo-mechanical coupling on residual stress in lithium niobate in surface acoustic wave device

Surface acoustic wave (SAW) devices are subject to thermomechanical coupling during operation, and when the temperature rises sharply to 180 °C, the surface of the lithium niobate crystal substrate generates nonuniform thermal stresses, thus leaving large residual stresses after complete cooling, which seriously influences its service performance and life. In this study, the thermal residual stresses of lithium niobate wafers were tested by nanoindentation tests, and the nanoindentation test process was simulated. The inverse calculation of the parameters of the lithium niobate constitutive model was carried out by comparing the load-displacement curves obtained from the finite element calculations with the experimental results. A multiscale model of the SAW device was established, its operation process was simulated, and then the generation law of residual stress was further discussed. The nanoindentation test results show that the thermal residual stress is positively correlated with the heating time under the effect of the same temperature; however, at the heating temperature up to about 180 °C, the lithium niobate crystal enters the high-temperature hyperelastic interval, and the yield stress of the crystal increases significantly at this stage. The constitutive model curves obtained by finite element calculations are in good agreement with the experimental results, and the thermal residual stress value of lithium niobate can reach 2/3 of its yield stress outside the high-temperature hyperelastic interval by comparison tests. The calculation results of the multi-scale model of the SAW device indicate that excessive thermal stress is the main cause of damage during the thermo-mechanical coupling of the SAW device. The polarization direction of lithium niobate crystals may cause the development of damage cracks, increasing the heat dissipation can effectively reduce the thermal stress to which it is subjected, and better extend the service life of the SAW device.

Performance Characterisation and Microscopic Characteristics of Rapeseed Heavy Oil–Diatomaceous Earth Composite-Modified Asphalt

In order to further improve the performance of bio-asphalt, because of its poor high-temperature performance, another biomass material, diatomaceous earth, was employed as a composite modifier, and a composite-modified asphalt was made to increase the high-temperature performance of bio-asphalt. The optimal preparation parameters of a rapeseed heavy oil–diatomaceous earth composite-modified asphalt were identified by employing an orthogonal test design. Based on the laboratory test, the physical properties, rheological properties, and microscopic properties of the asphalt were evaluated correspondingly by utilising matrix asphalt, rapeseed heavy oil-modified asphalt, and diatomaceous earth-modified asphalt as the control group. The results of the orthogonal test analysis showed that the optimum preparation parameters of the rapeseed heavy oil–diatomaceous earth composite-modified asphalt were 8% rapeseed heavy oil, 5% diatomaceous earth, a shear period of 35 min, and a shear rate of 2500 r/min. The addition of rapeseed heavy oil improved the fatigue resistance and low-temperature performance of the asphalt, but, at the same time, the asphalt penetration increased, the softening point and viscosity decreased, and the high-temperature rutting resistance decreased. Compared with the matrix asphalt, the viscosity of the rapeseed heavy oil–diatomaceous earth composite-modified asphalt at 135 °C rose by 23.2%. The rutting factor G*/sinδ increased by 45.5%, 15.6%, 17.6%, 29.8%, and 22.0%, while the fatigue factor G*·sinδ increased by 41.9%, 14.2%, 16.7%, 19.4%, and 23.1%, respectively, in the high-temperature rheological properties test temperature interval from 52 °C to 76 °C. The creep stiffness S fell by 16.2%, 36.1%, and 25.2%, while the creep rate m rose by 25.8%, 52.9%, and 13.4%, respectively, in the low-temperature rheological performance test temperature interval from −24 °C to −12 °C. Therefore, diatomaceous earth may effectively counteract the softening effect of the rapeseed heavy oil on the matrix asphalt and may raise the strength level and permanent deformation resistance of the composite-modified asphalt with only partial loss of fatigue resistance. The matrix asphalt, rapeseed oil, and diatomaceous earth exhibited high compatibility. The integration of rapeseed oil and diatomaceous earth largely did not modify the chemical properties of asphalt, and it was able to maintain the qualities of asphalt itself. Rapeseed heavy oil and diatomaceous earth on the thermal stability of the matrix asphalt has the opposite effect. The reorganisation component of diatomaceous earth on the colloidal structure of asphalt is conducive to the stabilisation of the nature of the asphalt, which can significantly improve the temperature stability of asphalt.

A Tabu-Matching Heuristic Algorithm Based on Temperature Feasibility for Efficient Synthesis of Heat Exchanger Networks

The non-structural model of heat exchanger networks (HENs) offers a wide solution space for optimization due to the random matching of hot and cold streams. However, this stochastic matching can sometimes result in infeasible structures, leading to inefficient optimization. To address this issue, a tabu matching based on a heuristic algorithm for HENs is proposed. The proposed tabu-matching method involves three main steps: First, the critical temperature levels—high, medium, and low-temperature intervals—are determined based on the inlet and outlet temperatures of streams. Second, the number of nodes is set according to the temperature intervals. Third, the nodes of streams are flexibly matched within the tabu rules: the low-temperature interval of hot streams with the high-temperature interval of cold streams; the streams crossing cannot be matched. The results revealed that by incorporating the tabu rules and adjusting the number of nodes, the ratio of the feasible zone in the whole solution domain increases, and the calculation efficiency is enhanced. To evaluate the effectiveness of the method, three benchmark problems were studied. The obtained total annual costs (TACs) of these case studies exhibited a decrease of USD 4290/yr (case 1), USD 1435/yr (case 2), and USD 11,232/yr (case 3) compared to the best published results. The results demonstrate that the proposed tabu-matching heuristic algorithm is effective and robust.

NOx emission deterioration in modern heavy-duty diesel vehicles based on long-term real driving measurements

NOx emissions from diesel vehicles generally deteriorate with increased durability mileage owing to the wear and deterioration of engines and after-treatment systems. Three China-VI heavy-duty diesel vehicles (HDDVs) were selected for four-phase long-term real driving emission (RDE) tests using the portable emission measurement system (PEMS). After 200,000 km of on-road driving, the maximum NOx emission factor of the test vehicles (387.06 mg/kWh) was found to be significantly lower than the NOx limit of 690 mg/kWh. Under all driving conditions, the NOx conversion efficiency of selected catalytic reduction (SCR) decreased almost linearly as the durability mileage increased. Importantly, the deterioration rate of the NOx conversion efficiency in low-temperature intervals was discernibly higher than that in high-temperature intervals. The NOx conversion efficiency at 200 °C dropped by 16.67–19.82% with higher durability mileage; however, the highest values at 275–400 °C only decreased by 4.11%. Interestingly, the SCR catalyst at 250 °C showed strong NOx conversion efficiency and durability (maximum decline of 2.11%). Overall, the poor de-NOx performance of SCR catalysts at low temperatures significantly challenges the long-term effective control of NOx emissions from HDDVs. Thus, improving the NOx conversion efficiency and durability at low-temperature intervals is the top priority for SCR catalyst optimization; NOx emissions from HDDVs at low velocities and loads should also be monitored by environmental authorities. The linear fitting coefficient for the NOx emission factors of the four-phase RDE tests was 0.90–0.92, indicating that NOx emissions deteriorated linearly with an increase in mileage. Based on the linear fitting results, the NOx emission control of the test vehicles during 700,000 km of on-road driving was highly likely to be qualified. These results can be used by environmental authorities to supervise the NOx emission conformity of in-use HDDVs after validation using other types of vehicles.

Extraction of helium from neon-helium mixture by the adsorption method

Helium is an importantnatural resourceand it hasgreat importance for scientific research. It is currently extracted mainly from natural gas or inlarge air separation units. Heliumandneonareusually separatedfrom an separationcolumntogether. In order to obtain pure neon and helium they are further purified. This article discusses the main methods of extracting helium from the neon-helium mixture.Having compared rectification, freezing, membrane separation and sorption methods, the authors concluded that the adsorption method allows separation at relatively high temperature intervals and is more energy-efficient than the other methods considered. The paper presents existing examples of the application of the adsorption method for the purification of helium from neon, which have been implemented in Chinaand in the CIS. An overview of adsorption separation on new adsorbents, both on metal-organic bases and on single-walled carbon nanotubes, is also presented. In the future, the authors will conduct experiments to fill in the data gaps on adsorption and desorption of neon-heliummixture on different adsorbents.

Thermal-Resistance Effect of Graphene at High Temperatures in Nanoelectromechanical Temperature Sensors.

Graphene membranes act as temperature sensors in nanoelectromechanical devices due to their excellent thermal and high-temperature resistance properties. Experimentally, reports on the sensing performance of graphene mainly focus on the temperature interval under 400 K. To explore the sensing performance of graphene temperature sensors at higher temperature intervals, micro-fabricated single-layer graphene on a SiNX substrate is presented as temperature sensors by semiconductor technology and its electrical properties were measured. The results show that the temperature coefficient of the resistance value is 2.07 × 10-3 in the temperature range of 300-450 K and 2.39 × 10-3 in the temperature range of 450-575 K. From room temperature to high temperature, the "metal" characteristics are presented, and the higher TCR obtained at higher temperature interval is described and analyzed by combining Boltzmann transport equation and thermal expansion theory. These investigations provide further insight into the temperature characteristics of graphene.

The Properties of Thermochemical Remanent Magnetization Acquired by Slow Laboratory Cooling of Titanomagnetite-Bearing Basalt Samples from Different Temperatures and the Results of the Thellier Method

—The experiments have been carried out on the acquisition of thermochemical remanent magnetization (TCRM) in basalt samples containing titanomagnetite (TM) with the Curie temperature Тс ~200°C by their rapid heating to maximum temperatures Т* from 450 to 530°C followed by slow cooling in the laboratory magnetic field Blab. At different stages of the preliminary thermal treatment of the initial samples, a set of magnetomineralogical studies including electron microscopy, X-ray diffraction and thermomagnetic analyzes, and measurements of magnetic hysteresis parameters were performed. It is shown that as early as the very beginning of the cooling process, all samples demonstrate explosive growth of TCRM corresponding to the stage of rapid single-phase oxidation of the initial titanomagnetite fraction of basalt, and that TCRM is acquired by the increase of Тс and volume of single-phase oxidized parts of TM grains as well as by the growth of the volume of Ti-depleted (relative to the initial TM) cells of microstructure of the subsequent oxidative exsolution. The Arai–Nagata diagrams for the samples carrying TCRM have a form of a broken line consisting of two linear segments. The low-temperature interval T < Т* corresponds to a mixture of thermochemical and thermoremanent (TRM) magnetizations and gives a slightly overestimated Blab because of the effect of a low cooling rate during the acquisition of TCRM and TRM. The high-temperature interval corresponds to pure TCRM and the Blab strength determined from this interval is underestimated by 20–27%. It is recommended to reject samples whose Araii–Nagata diagram has two or more linear segments against the background single-component NRM.

Bin Weather Data for HVAC Systems Energy Calculations

The increase in global air temperature is well documented, as during the last several years each decade has been consecutively warmer than the preceding. As climatic conditions affect the energy performance of buildings, the changes in outdoor air temperature and humidity will inevitably lead to significant alterations in energy consumption and costs for the heating, ventilating and air conditioning (HVAC) of buildings. The availability and quality of climatic data play an important role in the accuracy of energy analysis results. In this study, the hourly temperature and relative humidity of outdoor air measurements, for a period of three decades (1983–2012), recorded at the climatic station of the National Observatory of Athens were processed, and an up-to-date set of specific data for the application of bin methods was produced and presented. The data were then used to calculate changes in the energy demands in a typical office building throughout the specified period. Results showed a progressive reduction in the low and increase in the high temperature intervals, leading to an increase in the building’s annual energy requirements for air conditioning of up to 14.5% from the first to the third decade, with decrease in the energy demands for heating and increase in the energy demands for cooling.

Universal temperature corrections to the conductivity of niobium-carbon nanocomposites

The evolution of wide-temperature range (4.2–300 K) electron transport in niobium-carbon nanocomposites was studied at niobium concentration range 0.15–0.35. It was found that electron transport in the nanocomposites has the features of universality, being expressed in the existence of two characteristic temperature intervals on the temperature dependences of conductivity. The crossover temperature between the intervals is in the range 20–30 K. Within each temperature interval, corrections to the conductivity are found to be as power-like ones. Power exponent p is characterized by the non-monotonic dependences on niobium concentration and varies in the ranges 0.5–1.4 and 0.2–1.4 in the low- and high-temperature intervals with a minimum at 0.30 and 0.27 of Nb content, respectively. The satisfactory description of electron transport in niobium-carbon nanocomposites was achieved within the model of the inelastic tunneling of the electrons between the metal grains in the framework of the effective medium approximation.

Effect of potassium on the pyrolysis of biomass components: Pyrolysis behaviors, product distribution and kinetic characteristics

Potassium is an inorganic mineral element in biomass and has a significant catalytic effect on biomass pyrolysis. In this work, the effect of potassium on the pyrolysis of biomass components (cellulose, xylan and lignin) was investigated with the help of thermogravimetric analyzer coupled to fourier transform infrared spectrometer (TG-FTIR) and pyrolysis–gas chromatography coupled to mass spectrometry (Py-GC/MS). The results showed that potassium accelerated the start of the main pyrolysis stage of the biomass components, reduced the weight loss rate for cellulose and lignin, and increased the weight loss rate for xylan. On the other hand, potassium presented a promotion effect on the formation of char for cellulose but a suppression effect for lignin. In addition, an increasing potassium content promoted the release of volatile products for xylan. Product distribution analysis found that potassium promoted the scission of glycosidic bonds and the decomposition of glucose units, resulting in a sharp yield decrease of carbohydrates and a yield increase of furans, aldehydes and ketones. In addition, an increased production of CO2 was obtained, indicating that potassium favors the cleavage and reforming of carboxyl (COOH) and carbonyl (CO) groups. Furthermore, the effect of potassium on the pyrolysis of cellulose and xylan was stronger than that on lignin pyrolysis. The effect on the pyrolysis reaction also resulted in a higher activation energy for the decomposition of biomass components, especially at high temperature intervals. Moreover, the higher the content of potassium added, the greater the increase was in the activation energy.

Определение эффективной температуры обработки углеродных материалов в высокотемпературных печах по параметрам спектроскопии комбинационного рассеяния образцов-свидетелей

The aim of this work is to evaluate the use of Raman spectroscopy of carbon fibre-based (CF) reference samples for establishing the heat treatment temperature (HTT) in high-temperature (1000 – 3000 °C) furnaces used in production of a series of carbon materials. Based on obtained correlational relationships between Raman spectroscopy parameters and HTT, the use of the ID/IG parameter is suggested for obtaining the most exact and reproducible results. An experimental basis for the use of polyacrylonitrile-based (PAN) CF as reference specimens is provided. It is shown that for PAN-based CF samples treated in the high temperature interval (1000 – 3000 °С) the ID/IG parameter correlates well with X-Ray diffraction analysis parameters. A series of Raman spectroscopy of reference specimens potential uses the in determination of effective HTT of carbon materials in technological processes of production of carbon-carbon based composite materials, artificial graphites and PAN-based CF’s and in the determination of temperature fields of laboratory and industrial equipment for high-temperature treatment of carbon materials in the temperature interval 1000 – 3000 °C, specifically Tamman, vacuum electric resistance and Acheson furnaces, are examined.

The Correlation of Temperature-Mineral Phase Transformation as a Controlling Factor of Thermal and Mechanical Performance of Fly Ash-Based Alkali-Activated Binders.

This research focuses on an evaluation of mineral phase and structure transformations in Class F fly ash-based geopolymer systems. The research also studies the strength response of geopolymers when exposed to temperatures between 25 and 800 °C. The purpose of this research is to understand the processes that occur in alkali-activated systems within a wide range of high-working temperatures. The XRD, SEM, and DTA/TG analyses performed for the alkali-activated compositions after exposure to different temperatures confirmed a direct correlation of structural transformations with strength performance. The detrimental effect of sodium hydrocarbonate Na3(HCO3)(CO3) 2H2O or trona contained in one of the fly ash products was observed for the corresponding alkali-activated composite under high-temperature exposure between 600 and 800 °C. It was also detected that a high-temperature interval of 400–800 °C created favorable conditions that helped to form nanosized nepheline crystals and an additional vitreous substance that also contributed to a denser alkali-activated matrix.

Simulation of acacia gasification process

This electronic document presents the thermokinetical modelling of the gasification process done on acacia-tree with variable operating conditions and different humidity levels. Gasification does not produce flue gas, but due to imperfect burning, synthesis gas appears which is rich in flammable components (CO2 and H2). The chemical structure of this gas depends on the components of the fuel and the humidity level, but greatly affected by the technological parameters too, such as pressure and temperature, as well as the air-ratio. The study shows the change in the amount of the fuel and the reaction efficiency, caused by varying gasification temperature and pressure. Rising temperature results in improved efficiency, while higher pressure worsens reaction efficiency. However, at higher temperature intervals, the effect of the pressure is neglectable.

Melting loops in the phase diagram of individual nanoscale alloy particles: completely miscible Cu–Ni alloys as a model system

A modified thermodynamic approach to describe melting in isolated nanoscale materials is suggested. The Gibbs free energy change of nanoscale alloy particles is modeled as a function of composition, temperature and nucleus and particle sizes. Cu–Ni has been chosen as a model system due to the availability of thermodynamic data within the high-temperature interval 1300–1600 K. For the first time, “melting loops” in the temperature–composition phase diagram were calculated for nanoparticle of 25 and 80 nm, respectively. It is shown that such loops represent the equilibrium two-phase solid–liquid states and do not coincide with the limiting solubility curves—the solidus and the liquidus. This new finding leads to the “melting loop” concept concerning phase diagrams of nanoscale alloys introduced in this paper. It is found that Cu–Ni nanoparticles can melt in different ways, whereas the dominant transition mechanism is surface-induced melting that initiates from the surface and then proceeds toward the core region. The decrease in size causes also a change of the melting temperature, the temperature width of the phase transition, the solubility limit, the concentration width of the melting loop as well as a change of the shape and slope of the equilibrium curves of the two-phase region of the phase diagram. As expected, when the size of the nanoscale particle increases, the solidus temperature increases and the size-dependent phase diagram approaches the bulk phase diagram.

Static Softening Behavior of Low Carbon High Niobium Microalloyed Steel

The MMS-200 thermal simulation testing machine was used to study the static softening behavior of low carbon high niobium microalloyed steel. The effect of niobium to the static recrystallization softening behavior of the microalloy steel had been analyzed by establishing the kinetics model of static recrystallization and the micro-morphology of precipitates. The results indicated that: the static softening behavior of the tested steel significantly influenced by the deformation temperature and the interval pass time of the rolling processing. At relatively high deformation temperature and long interval pass time, the ratio of static softening was increased. Then the deformation temperature was lower to 950°C, and the static softening behavior of the test steel was ceased. But when the deformation temperature was higher than 1000°C, the static softening behavior of the test steel completely occurred. The activation energy of the test steel was 325·mol-1 by the established model calculated.

Effect of Gd addition on phase composition, structure, and properties of beta-solidifying TiAl-based alloy with Zr and Cr content variability

The aim of the present work was to study the influence of Gd microaddition on the sequence and temperatures of phase transformations as well as on the microstructural evolution and properties of a new six-component TiAl-based alloy Ti-44.5Al-2V-1Nb-xZr/yCr-(0 … 0.1)Gd (at.%) with variable Zr (x = 0.5–1.5 at.%; eq. 1.2–3.5 wt%) and Cr (y = 1.5–2.5 at.%; eq. 2.0–3.5 wt%) content in the as-cast condition using thermodynamic calculations in Thermo-Calc software and experimental methods including differential scanning calorimetry, in-situ high-temperature X-ray diffraction analysis, optical, scanning, and high-resolution transmission microscopy. It was demonstrated that in all compositions of the studied alloy the sequence of phase transformations at high temperature interval includes L→β, β→α, and α→γ transformations, passing through the single-phase β and α fields. These are then followed by a three-phase eutectoid reaction α→α2+γ in Zr-containing compositions and further by a four-phase α→α2+γ+β reaction in Cr- and (Zr+Сr)-containing compositions. It has been revealed that the addition of 0.1 at.% Gd does not change the sequence and temperatures of these phase transformations. Nevertheless, the formation of nano-particles, identified as base-centered monoclinic Gd2O3 oxide located in Zr-containing compositions inside the γ lamellae and in Cr- and (Zr + Cr)-containing compositions on the boundaries of the γ lamellae and inside the β phase interlayers and being coherent with the β0 phase, results in reduction of (α2+γ) colony size in the as-cast condition (VAR + VAR + VIM) down to 100 ± 10 μm. It has been also found that ultimate tensile strength and plastic elongation in Zr- and Cr-containing compositions of the studied alloy in the as-cast condition measured at room temperature are 473 ± 8 MPa, 1.1 ± 0.1% and 513 ± 10 MPa, 1.4 ± 0.1%, respectively. The addition of 0.1 at.% Gd results in plastic elongation increasing to (1.3–1.6)±0.1%, while remaining the strength unaffected.

Reactive wetting behavior and mechanism of AlN ceramic by CuNi-Xwt%Ti active filler metal

In order to propel the application of the developed CuNi-Xwt%Ti active filler metal in AlN brazing and get the universal reactive wetting mechanism between liquid metal and solid ceramic, the reactive wetting behavior and mechanism of AlN ceramic by CuNi-Xwt%Ti active filler metal were investigated. The results indicate that, with the increasing Ti content, surface tension for liquid CuNi-Xwt%Ti filler metal increases at low-temperature interval, but very similar at high-temperature interval, which influence the wetting behavior on AlN ceramic obviously. CuNi/AlN is the typical non-reactive wetting system, the wetting process including rapid wetting stage and stable stage. The wettability is depended on surface tension of the liquid CuNi filler metal completely. However, the wetting process of CuNi-8wt.%Ti/AlN and CuNi-16 wt%Ti/AlN reactive wetting system is composed by three stages, which are rapid wetting stage decided by surface tension, slow wetting stage caused by interfacial reaction and stable stage. For CuNi-8wt.%Ti/AlN and CuNi-16 wt%Ti/AlN reactive wetting system, although the surface tension of liquid filler metal is the only factor to influence the instant wetting angle θ0 at rapid wetting stage, the reduced free energy caused by interfacial reaction at slow wetting stage plays the decisive role in influencing the final wettability.