Surface Of Ceramic Samples Research Articles

Influence of debinding parameter and nano-ZrO2 particles on the silica-based ceramic cores fabricated by stereolithography-based additive manufacturing

The silica-based ceramic core is an essential part of the investment casting of hollow turbine blades due to their excellent thermal stability and easy demoulding. In this study, the green bodies of silica-based ceramic cores with nano-ZrO2 were fabricated by stereolithography (SLA). Firstly, the effects of the burying process and debinding heating rates on the performance and microstructure of silica-based cores were investigated. The results revealed that the burying powders provide support and a stable thermal field for the SLA ceramic cores during debinding and sintering. Ceramic cores with smaller shrinkage and higher apparent porosity were produced during the burying process at a heating rate of 0.5 °C/min. In addition, the influence of nano-ZrO2 content on the mechanical properties of silica-based ceramics was investigated. Nano-ZrO2 particles can improve bulk density and mechanical properties by promoting sintering. Additionally, it can reduce the cracks on the surface of ceramic samples. The optimal content of nano-ZrO2 should be between 1.5 and 2 wt%, producing silica-based cores with low shrinkage rate (2.91–3.19%), high apparent porosity (27.11–27.97%) and high flexural strength at room temperature (24.51–24.65 MPa) and high temperature (27.81–29.69 MPa). This work provides promising ways to fabricate high-quality ceramic cores for turbine blade application.

Influence of the preparation conditions on the electrical properties with negative temperature coefficient

The CaCu₃Ti₄O₁₂ ceramics have been successfully prepared by the sol-gel method. We have set four different temperature gradients (950℃, 1000℃, 1050℃, 1100℃) as the sintering temperatures for CaCu₃Ti₄O₁₂ ceramics to study the influence of different temperatures on the thermistor. The effects of different sintering temperatures on the structure of CaCu₃Ti₄O₁₂ ceramics were analyzed by X-ray diffraction (XRD). Scanning electron microscope (SEM) images demonstrate that the grain size of ceramic samples will increase with the increase of the sintering temperature. X-rayphotoelectron spectroscopy (XPS) has been used to study the chemical states on the surface of ceramic samples. It is confirmed that the coexistence of Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺ is the cause of the conductivity of CaCu₃Ti₄O₁₂ ceramics. All ceramic samples have NTC behavior, room temperature resistivity (ρ₂₅), material constant (B) and the relationship between the nature logarithm of the resistivity and the temperature has been studied in this paper.

Effect of Laser Perforation of Elements of a Diffusion-Bonded Ceramic–Copper–Ceramic Joint on Its Mechanical Properties

The effect of surface laser preprocessing of silicon nitride samples and copper gaskets on the properties of diffusion-bonded ceramic–metal–ceramic joints has been studied experimentally. The results demonstrate that laser perforation of metallic gaskets and laser drilling of holes in the surface of ceramic samples considerably improve the mechanical properties of solid-state diffusion-bonded joints.

Wavelet analysis of ceramic surface images as a method for measuring the size of structural elements

The expediency of applying the wavelet analysis method to visualize and measure structural elements on the surface of ceramic samples is shown. The experimental results of image processing of the surface of samples made of kaolin clay using wavelet analysis are presented. Examples of applying the wavelet transform to the study of model images with simple geometry and precisely known sizes of structural elements of the “checkerboard” type are considered. A relation is proposed that relates the particle size to the scale parameter of the wavelet spectrum. A simple and modern method makes it possible to record and quantify the structural changes occurring in highly dispersed ceramic samples under the influence of a microwave field. It was found that on the surface of ceramic samples processed in a microwave field, the sizes of structural elements (particles) are reduced by an average of 20%; the surface itself becomes more uniform. This effect is extremely promising for the development of technology for producing finely dispersed ceramic materials.

Aluminum Ion Beam Treatment of Zirconium Ceramics

The paper presents the radiation and thermal treatment of zirconium ceramics with high-energy Al ion beams generated at an accelerating voltage of 1.5 kV, which modifies the structure and electrophysical properties of zirconium ceramics. Compact powder and ceramic samples are used for the radiation and thermal treatment performed at 1123–1173 K. The surface treatment of compact powders leads to the increase in the grain size, whereas the surface of ceramic samples turns black and electrically conductive in depth. This is because the change in the oxygen stoichiometry of zirconium ceramics. Air annealing of treated ceramics returns the sample to the initial state. The phase composition, microhardness and density of ceramic samples display no changes after the radiation and thermal treatment. Under the experimental conditions, the diffusion of aluminum ions in the surface layer is not observed. It is found that the ion beam treatment leads to the decrease in aluminum-containing impurity in the surface layers of zirconium ceramics.

Dynamic Fracture Toughness of TaC/CNTs/SiC CMCs Prepared by Spark Plasma Sintering

This study focuses on the fracture toughness of TaC and carbon nanotubes (CNTs) reinforced SiC ceramic matrix composites (CMCs), prepared by spark plasma sintering (SPS) technique. A high densification of 98.4% was achieved under the sintering parameter of 133°C/min, 1800°C, and 90 MPa pressure. Vickers indentation was employed to measure the indentation toughness on the polished surface of ceramic samples, SEM was applied to directly observe the crack propagation after indentation, and split Hopkinson pressure bar (SHPB) was developed to determine the dynamic fracture toughness within the ceramic samples subjected to an impact in a three-point bending configuration.

Peculiarities of Surface Fracture of B<sub>4</sub>C Ceramics under Loads

The paper presents experimental results showing the nature of the destruction in the surface layer of В4С ceramics during hardness and fracture toughness tests performed by Vickers diamond pyramid indentation with different applied loads (4.91 - 294.3 N). Ceramics made from boron carbide powder with 10 wt.% additive of submicron fraction of the same powder sintered in spark discharge plasma by Spark Plasma Sintering (SPS-method) under different sintering conditions was studied. Changes of micro hardness and hardness of the samples were measured by micro hardness tester PМТ-3М with the loadsРup to 4.9 N; by micro hardness tester Micromet withP=9.811.77 N; and by hardness tester ТP-7R-1 with the loads of 49 - 294.3 N. Indentation, exposure, and unloading were carried out according to standard method during 30-40 seconds. The microstructure and topography of the surface of ceramic samples splits after indentation were studied by scanning electron microscopy (SEM, microscope JEOL SEM-7500FA). The profiles of the split surface depth were determined by Linnik interferometer МII-4.

Analysis of Surface Reaction Mechanisms on Electrically Non-Conductive Zirconia, Occurring within the Spark Erosion Process Chain

Electrically insulating high performance ceramics like zirconia are increasingly used for high technological applications due to their extraordinary properties. Meanwhile even the spark erosion process can be used to structure non-conductive ceramics by using an assisting electrode (AE). This conductive AE is placed on top of the work piece to enable the process. The electrical contact is sustained during the process by carbonic residua of cracked oil used as a dielectric. For an enhanced understanding of the removal mechanisms during the spark erosion process of such non-conductive ceramics, we analysed the surface of ceramic samples during the entire spark erosion process chain. In our investigation a zirconium oxide with yttrium oxide stabilisation was chosen. For this purpose X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis was performed. The XRD results showed that the zirconium oxide reacts under the presence of carbonic residua during processing into zirconium carbide. This material supports sustaining the conductivity additionally, as it is conductive itself. In a subsequent thermal cleaning step with oxide atmosphere (T = 750°C), remaining carbonic residua are oxidised and thus removed. The XRD measurements after cleaning showed that the zirconium carbide was no longer detectable. Instead a monoclinic zirconium phase was found. This shows that a reverse reaction of zirconium carbide into zirconium oxide took place. To prevent the formation of a non-stabilised monoclinic phase, the oven process was adapted to higher temperatures of 900°C with higher heating and active cooling rates of up to 10 K/s. This adjustment shows that the monoclinic phase can be supressed and the reverse reaction leads to a tetragonal zirconium oxide like the bulk material.

Thermocapillary mechanism of pore evaporation during sintering and crystallization of YBa2Cu3O7− δ

The thermocapillary effect is used to explain the phenomenon of shrinkage observed during the annealing of YBa2Cu3O7−δ components. The proposed model can be used to estimate the characteristic time taken for pores to reach the surface of ceramic samples.