Mechanical properties of fusion welded ceramics in the SiC-ZrB2 and SiC-ZrB2-ZrC systems

Mechanical properties of welded SiC-ZrB₂ and SiC-ZrB₂-ZrC ceramics were measured up to 1700 °C. Commercial powders were hot pressed, machined into coupons, and preheated to 1600 °C before joining the ceramics using either tungsten inert gas welding or plasma arc welding. Toughness of the parent materials was 3–4 MPa*m^1/2 which decreased after welding to 2–2.5 MPa*m^1/2. Strength of the SiC-ZrB₂-ZrC parent material was ~700 MPa at 25 °C, ~300 MPa at 1700 °C, and retained 40–60% of this strength once welded. Strength of the SiC-ZrB₂ parent material was ~600 MPa at 25 °C and 1700 °C and retained 20–30% of this strength once welded. Griffith analysis indicated that the strength in the parent materials was controlled by the size of SiC clusters while strength of welds was controlled by the size of pores in fusion zones. Therefore, removal of pores in produced fusion zones should be investigated to improve strength of future ceramic welds.     

Structure,electrical and luminescent properties of the NBT:Er-0.3CT:Pr composite ceramics

A binary composite ceramic Na_0.5Bi_0.5TiO₃:0.002 Er-0.3CaTiO₃:0.003 Pr (NBT:Er-0.3CT:Pr) was fabricated by a conventional solid state reaction route. The effect of sintering temperature on the microstructure and phase structure of the ceramics has been investigated. And the basic electrical properties such as dielectric properties and ferroelectric performances of the ceramics were examined. Macro long-ranged ferroelectric order cannot be induced via electric field in the composite ceramics. And under local electric field using PFM, obvious ferroelectric switching is identified in the ceramics. Furthermore, the up-conversion luminescence, photochromic reaction, and luminescence modulation have been achieved in the ceramics. Additionally, photo-stimulated luminescence and thermal luminescence are obtained. The present study indicates that optical properties are tightly related to the sintering temperature. The prepared ceramic NBT:Er-0.3CT:Pr owns a piezoelectric performance and multi luminescence properties, which can widen the applications of ferroelectric ceramics.     

Effects of porosity on electrical and thermal conductivities of porous SiC ceramics

The effects of porosity on the electrical and thermal conductivities of porous SiC ceramics, containing Y₂O₃–AlN additives, were investigated. The porosity of the porous SiC ceramic could be controlled in the range of 28–64 % by adjusting the sacrificial template (polymer microbead) content (0–30 wt%) and sintering temperature (1800–2000 °C). Both electrical and thermal conductivities of the porous SiC ceramics decreased, from 7.7 to 1.7 Ω⁻¹ cm⁻¹ and from 37.9 to 5.8 W/(m·K), respectively, with the increase in porosity from 30 to 63 %. The porous SiC ceramic with a coarser microstructure exhibited higher electrical and thermal conductivities than those of the ceramic with a finer microstructure at the equivalent porosity because of the smaller number of grain boundaries per unit volume. The decoupling of the electrical conductivity from the thermal conductivity was possible to some extent by adjusting the sintering temperature, i.e., microstructure, of the porous SiC ceramic.     

Synthesis and thermoelectric properties of (NaxCa1−x)3Co4O9 ceramics

(Na_xCa_1−x)₃Co₄O₉ (x=0.05−0.2) ceramics with a layered crystal structure were prepared by a sol–gel method followed by a low-temperature sintering procedure. The electrical conductivity and Seebeck coefficient of the complex oxide ceramics were measured from 400 to 900 °C. Their electrical conductivity and power factor increase with increasing temperature, while the thermal conductivity is very weakly dependant on the temperature. Na dopant amount has a remarkable effect on electrical and thermal transport properties. The figure of merit in the ceramic samples is smaller than that of traditional thermoelectric alloys.     

Effect of hot-pressing sintering on thermal and electrical properties of AlN ceramics with impedance spectroscopy and dielectric relaxations analysis

The effects of hot-pressing sintering on the phase composition, microstructure, thermal and electrical properties of AlN ceramics with CeO₂–CeF₃ additives were studied. During hot-pressing sintering, high pressure reduced the grain boundary phase CeAlO₃ and decreased the concentration of oxygen in AlN ceramics. The hot-pressing sintered AlN samples had a much higher thermal conductivity of 191.9 W/m·K than pressureless sintered ones because of the great reduction of grain boundary phases and oxygen impurities in AlN ceramic. As the carbon content in hot-pressing sintered sample was very high, carbon contamination led to the decrease in electrical resistivity and changes in polarization mechanisms for AlN ceramics. The relaxation peak in the dielectric temperature spectrum with an activation energy of 0.64 eV for hot-pressing sintered samples was caused by electrons from free carbon at low temperature. Overall, hot-pressing sintering can effectively increase the thermal conductivity and change the electrical properties of AlN ceramics.     

Recent advances and perspectives in carbon-based fillers reinforced Si3N4 composite for high power electronic devices

New advances in carbon-based fillers (CBFs) as reinforcing agents have gained worldwide attention due to their novel properties and promising applications to obtain advanced composite materials with superior electrical, mechanical and thermal performance. These CBFs (carbon nanotubes (CNTs), carbon nanofibers (CNFs), graphene, graphene oxide, and graphite) are important for ceramic materials to make them more attractive for modern industry. These materials in the ceramic matrix can enhance various properties, such as mechanical, thermal, and electrical conductivity, as a sensor material for pressure and other environmental changes. This overview introduces the latest developments in the fabrication of Si₃N₄ ceramics and the effect of CBFs as well SiC and SiC_w on structural, mechanical, and thermal properties of Si₃N₄ ceramics for next-generation electronic power devices. Moreover, we summarized the key aspects such as the fabrication approaches, influence of additive composition and concentration, and sintering parameters on the microstructure and overall performance of Si₃N₄ ceramics. In particular, design strategies for scientists and engineers concerned about the manufacture of Si₃N₄ substrate and active regeneration for the first time are proposed and discussed extensively.     

Characterization of fusion welded ceramics in the SiC-ZrB2-ZrC system

Various SiC-ZrB₂-ZrC ceramics were joined by fusion welding to determine the maximum silicon carbide content that could be joined. Commercial powders were hot pressed, machined, and preheated to 1450 °C before joining with a tungsten inert gas welding torch at 160–200 A. Resulting welds were cross-sectioned and analyzed to determine which compositions were weldable and to characterize microstructural evolution in welded samples. As compositions approached the ternary eutectic, the welds had smaller SiC grains and exhibited better weldability. Penetration depth of welds was controlled by a combination of current input and welding speed. The ternary eutectic in the system was found at 36.9 ± 1.3 vol% SiC, 42.7 ± 1.5 vol% ZrB₂, and 20.4 ± 1.9 vol% ZrC and its melting temperature was 2330 ± 23 °C. A ternary phase diagram for the SiC-ZrB₂-ZrC was constructed and proposed via microstructural analysis of arc melted pellets on binary joins between each binary eutectic and the ternary eutectic in the system.     

Piezoelectricity,thermal stability,and fatigue resistance in Nb and Ta-doped Bi4Ti3O12 high-temperature piezoceramics

The effect of Nb/Ta donor doping on the piezoelectricity, thermal stability, and fatigue resistance of bismuth titanate Bi₄Ti₃O₁₂ (BIT) ceramics was investigated in relation to their structural and oxygen vacancy-related electrical properties. As the Nb/Ta doping amount increased, the activation energy of oxygen vacancy conduction increased, indicating a reduction in the concentration of oxygen vacancies. The improved electrical insulating properties of the Nb/Ta-doped Bi₄Ti₃O₁₂ ceramics (BTNT) with fewer oxygen vacancies, contributed to their effective poling and strong piezoelectricity. Outstanding piezoelectric performance with high piezoelectric constant (39 pC/N) and Curie temperature (690 °C) could be achieved in the 0.005 mol Nb/Ta-doped BTNT ceramic with high density and anisotropic grain growth. The BTNT ceramics exhibited superior thermal aging stability and fatigue resistance compared to the BIT ceramic, suggesting that the reduction of oxygen vacancy defects plays a decisive role in enhancing elevated-temperature-induced and electric-field-induced degradation stabilities.     

High thermal-conductivity rGO/ZrB2-SiC ceramics consolidated from ZrB2-SiC particles decorated GO hybrid foam with enhanced thermal shock resistance

Graphene derivative materials exhibit excellent mechanical and thermal properties, which have been extensively used to toughen ceramics and improve thermal shock resistance. To overcome the thermal agglomeration of graphene oxide (GO) during heating and drying process, ZrB₂-SiC particles decorated GO hybrid foam with uniformly anchored ceramic particles was synthesized by electrostatic self-assembly and liquid nitrogen-assisted freeze-drying process. Densified rGO/ZrB₂-SiC ceramics with varying microstructure, thermal physical and mechanical properties were obtained by adjusting the content of decorated ceramic particles. Although the flexural strength of rGO/ZrB₂-SiC ceramics have an attenuation compared with that of ZrB₂-SiC ceramic, the thermal conductivity, work of fracture and thermal shock resistance are greatly improved. rGO/ZrB₂-SiC ceramics exhibit delayed fracture and increasing R-curve behavior during the crack propagation. The novel preparation technology allows for the well dispersion of rGO in ZrB₂-SiC ceramics and can be easily extended to other ceramic or metal materials systems.     

Effects of frequency on electrical fatigue behavior of ZnO-modified Pb(Mg1/3Nb2/3)0.65Ti0.35O3 ceramics

This work aims to study the effects of frequency on the electrical fatigue behavior of ZnO-modified Pb(Mg_1/3Nb_2/3)_0.65Ti_0.35O₃ (PMNT) ceramics. Changes in microstructures, ferroelectric and piezoelectric properties of the ceramics at bipolar electrical fatigue frequencies of 5, 10, 50 and 100 Hz were observed. The thickness of damaged surface of the ceramics decreased with increasing frequency. The degradation of properties of the ceramics fatigued at low frequency was greater than those fatigued at high frequency. The degradation by electrical fatigue at lower frequencies, 5 and 10 Hz, could be caused by the effects of both field screening and domain pinning, while at higher frequencies the fatigue was mainly a result of the field screening effect. The fatigue properties of ZnO-modified PMNT ceramics was compared to Pb-based and Pb-free ferroelectric ceramics. It was found that the fatigue endurance of ZnO-modified PMNT ceramic was greater than that of hard PZT ceramic but less than that of Pb-free ferroelectric ceramic.     

Ti3SiC2陶瓷粉末的制备

新型层状陶瓷材料Ti3SiC2集金属和陶瓷的优良性能于一身,如良好的导电导热性、耐氧化、耐热震、高弹性模量、高断裂韧性等,在高温结构陶瓷、电刷和电极材料、可加工陶瓷材料、自润滑材料等领域有着广泛的应用前景。本文综合介绍了Ti3SiC2粉末制备的研究进展。此外,作者以Ti／Si／C／Al元素粉为原料,采用无压烧结的方法制备出纯度较高的Ti3SiC2陶瓷粉末,为Ti3SiC2基复合材料的发展开辟了一条新途径。     

Wetting of ceramic materials by liquid silicon, aluminium and metallic melts containing titanium and other reactive elements: A review

The wetting properties of ceramic materials by liquid silicon, aluminium and metallic melts containing titanium and other reactive elements are reviewed on the basis of the current understanding and recent developments in the field of metal-ceramic wetting. For silicon and aluminium, attention is paid to the surface characteristics of both metals and ceramics, and to the effect of chemical reactions at the interfaces on the wettability. A special effort is made to analyse the Ti-induced wetting of ceramics in terms of the chemical reactivity and interface microchemistry. The importance of interactions between the interfacially active element (Ti) and other alloying elements in the metallic melts is elucidated with numerous experimental results.     

新型电刷材料Ti3SiC2的合成与研究进展

介绍了一种新型的电刷材料-Ti3SiC2陶瓷。Ti3SiC2结合了金属和陶瓷的许多优异性能，既具有与金属相似的良好的导热、导电性，良好的可加工性，相对柔软，抗热震性好，可塑性变形等；同时又具有与陶瓷相似的抗氧化、耐腐蚀、耐高温等特性，并且还有很好的自润滑性和超低摩擦系数，被认为在许多领域有着广泛的应用前景。     

新型层状陶瓷Ti3SiC2的研究进展

新型层状陶瓷Ti3SiC2兼有金属和陶瓷的许多优良性能,具有高的热导率和电导率,易加工,同时具有良好的抗热震性、抗氧化性和高温稳定性.本文从层状陶瓷Ti3SiC2制备方法、结构和性能等方面进行综述,并对其应用前景进行展望.     

新型层状陶瓷Ti3SiC2的研究进展

新型层状陶瓷Ti3SiC2兼有金属和陶瓷的许多优良性能，具有高的热导率和电导率，易加工，同时具有良好的抗热震性、抗氧化性和高温稳定性。本文从层状陶瓷Ti3SiC2制备方法、结构和性能等方面进行综述，并对其应用前景进行展望。     

Thermal shock and thermal fatigue resistance of Al2O3/(W,Ti)C/TiN/Mo/Ni multidimensional graded ceramics

Al₂O₃/(W, Ti)C/TiN/Mo/Ni multidimensional graded ceramics and homogeneous reference ceramic were prepared by two step hot press sintering. The thermal shock and thermal fatigue resistance of the multidimensional graded ceramics were tested using the water quenching method. Scanning electron microscopy (SEM) and optical microscope were used to investigate microscopic failure mechanism of ceramics. The results showed that the retained flexural strength of two-dimensional and one-dimensional graded ceramics was almost same, but higher than that of the homogeneous ceramic. The crack growth (∆c) of homogeneous ceramic increased rapidly, while that of two-dimensional graded ceramics is the lowest. Hence, thermal fatigue resistance of the two-dimensional graded ceramics was highest. The residual compressive stress in the first layer induced by the optimal graded structure played an important role. In addition, the increasing toughness on the crack propagation path by adding different amounts of metals was also a contributing factor.     

Electrical conductivity and infrared radiation performance of SiC-CNT composite ceramics

SiC ceramic is an excellent infrared source material that can be used in a wide range of fields, like infrared heating, night vision and communication, but its poor electrical properties limit it. In this work, carbon nanotubes (CNTs) were selected as conductive phase filler, and SiC-CNT composite ceramics were prepared by SPS method. The effects of CNT content on the microstructures, electrical properties and infrared radiation performance of the composites were studied. The introduction of CNT effectively reduced the height of Schottky barrier at grain boundary, thus weakening the grain boundary effect, reducing the grain boundary resistance, further weakening the nonlinear characteristics and bulk resistivity of the composite ceramics. When the content of CNT was 1 wt%, electrical percolation was achieved, and the bulk resistivity of SiC ceramics dropped by nearly 3 orders of magnitude. The preferred orientation distribution of CNT made the bulk resistivity perpendicular to the pressure direction R_⊥ always lower than that parallel to the pressure direction R_//. The sample with 5 wt% CNT assumed linear conductivity characteristics, with bulk resistivity in different direction of 16.5 Ω cm (R_//) and 11.8 Ω cm (R_⊥), respectively. CNT addition slightly increased the infrared radiation performance of SiC ceramics, and the sample with 5 wt% CNT possessed the highest total emissivity of 0.675. The excellent electrical conductivity and infrared radiation performance of SiC-CNT composite ceramic confirmed this class as a promising infrared source material.     

Role of CaF2 on mechanochemically synthesized leucite as dental veneering glass ceramics

Leucite based glass ceramic is widely used in dental ceramics as porcelain fused to metals for veneering applications. Main properties considered here are high coefficient of thermal expansion and good mechanical properties. Owing to these requirements, high expansion phase such as leucite is incorporated in these glass ceramics. The present work was aimed to synthesise leucite using its stoichiometric batch compositions and subsequent high energy ball milling. CaF₂ was also added in another mix to study its role on leucite formation. Further prepared, leucite phase was added in separately prepared low temperature glass frit powders to control amount of glass and leucite content. X-ray diffraction results displayed that high energy ball milling and additive promoted the formation of leucite as a major crystalline phase. Furthermore, CaF₂ also suppressed the subsidiary crystallisation of kalsilite phase. Evaluated average coefficient of thermal expansion in the temperature range of 20–500°C was very close to the theoretical value of pure leucite.     

Ti3SiC2陶瓷粉末的制备

新型层状陶瓷材料Ti3SiC2集金属和陶瓷的优良性能于一身,如低密度、高熔点、良好的导电导热性、高弹性模量、高断裂韧性、耐氧化、耐热震、易加工且有良好的自润滑性。在高温结构陶瓷、电刷和电极材料、可加工陶瓷材料、自润滑材料等领域有着广泛的应用前景。本文综合介绍了Ti3SiC2粉求制备的研究进展。最近,作者以Ti／Si／C／Al元素粉为原料,采用无压烧结的方法制备出纯度较高的Ti3SiC2陶瓷粉末。为Ti3SiC2基复合材料的发展开辟了一条新途径。     

Voltage-current characteristics of vanadium dioxide based ceramics

Voltage-current characteristics of VO₂ and V₂O₅–P₂O₅ glasses based ceramics with an addition of copper has been studied. The voltage-current characteristics are of S-type and have behaviour, which is typical for materials on the basis of vanadium dioxide. At some voltage the switching takes place and in a ceramic sample is formed the channel of electrical current. The VO₂ crystallites in this channel are in a metallic phase. The analytical expression for a voltage-current characteristic of a ceramic sample with the cylindrical channel of electrical current is obtained. The effective electrical conductivity and effective thermal conduction of vanadium dioxide based ceramics are increasing, the switching voltage is decreasing at increase of the content of copper additive. The probable reason of that is increase of amount of electrical and thermal bonds between VO₂ crystal grains through inclusions of copper, and also the decrease of a porosity of ceramics.