A superior SiC based thermal protection coating process for carbon composite, which can be especially effective in a hot oxidizing atmosphere, was established in this study. A multi-coating process based on a combination of Chemical Vapor Reaction (CVR) and Chemical Vapor Deposition (CVD) was developed. Various protective coating layers on carbon composite were tested in hot oxidizing surroundings and the test results verified that the thermal ablation rate could be dramatically reduced down to 3.8% when the protective multi-coating was applied. The thermal protection mechanism of the coating layers was also investigated.
This study manufactured a SiC coating layer using the vacuum kinetic spray process and investigated its microstructure and wear properties. SiC powder feedstock with a angular shape and average particle size of 37.4 μm was used to manufacture an SiC coating layer at room temperature in two different process conditions (with different degrees of vacuum). The thickness of the manufactured coating layers were approximately 82.4 μm and 129.4 μm, forming a very thick coating layers. The SiC coating layers consisted of α-SiC and β-SiC phases, which are identical to the feedstock. Cross-sectional observation confirmed that the SiC coating layer formed a dense structure. In order to investigate the wear properties, ball crater tests were performed. The wear test results confirmed that the SiC coating layer with the best wear resistance achieved approximately 4.16 times greater wear resistance compared to the Zr alloy. This study observed the wear surface of the vacuum kinetic sprayed SiC coating layer and identified its wear mechanism. In addition, the potential applications of the SiC coating layer manufactured using the new process were also discussed.
The paper discusses the application of the current-source concept in the gate drivers for silicon carbide transistors. There is a common expectation that all SiC devices will be switched very fast in order to reach very low values of switching energies. This may be achieved with the use of suitable gate drivers and one of possibilities is a solution with the current source. The basic idea is to store energy in magnetic field of a small inductor and then release it to generate the current peak of the gate current. The paper describes principles of the current-source driver as well as various aspects of practical implementation. Then, the switching performance of the driven SiC transistors is illustrated by double-pulse test results of the normally-ON and normally-OFF JFETs. Other issues such as problem of the drain-gate capacitance and power consumption are also discussed on the base of experimental results. All presented results show that the currentsource concept is an interesting option to fast and efficient driving of SiC transistors.
Preliminary tests aimed at obtaining a cellular SiC/iron alloy composite with a spatial structure of mutually intersecting skeletons, using a
porous ceramic preform have been conducted. The possibility of obtaining such a composite joint using a SiC material with an oxynitride
bonding and grey cast iron with flake graphite has been confirmed. Porous ceramic preforms were made by pouring the gelling ceramic
suspension over a foamed polymer base which was next fired. The obtained samples of materials were subjected to macroscopic and
microscopic observations as well as investigations into the chemical composition in microareas. It was found that the minimum width of a
channel in the preform, which in the case of pressureless infiltration enables molten cast iron penetration, ranges from 0.10 to 0.17 mm. It
was also found that the ceramic material applied was characterized by good metal wettability. The ceramics/metal contact area always has
a transition zone (when the channel width is big enough), where mixing of the components of both composite elements takes place.
439L stainless steel composites blended with fifteen micron SiC particles were prepared by uniaxial pressing of raw powders at 100 MPa and conventional sintering at 1350oC for 2 h. Based on the results of X-ray diffraction analysis, dissolution of SiC particles were apparent. The 5 vol% SiC specimen demonstrated maximal densification (91.5%) among prepared specimens (0-10 vol% SiC); the relative density was higher than the specimens in the literature (80-84%) prepared by a similar process but at a higher forming pressure (700 MPa). The stress-strain curve and yield strength were also maximal at the 5 vol% of SiC, indicating that densification is the most important parameter determining the mechanical property. The added SiC particles in this study did not serve as the reinforcement phase for the 439L steel matrix but as a liquid-phase-sintering agent for facilitating densification, which eventually improved the mechanical property of the sintered product.
This paper describes the study of thermal properties of packages of silicon carbide Schottky diodes. In the paper the packaging process of Schottky diodes, the measuring method of thermal parameters, as well as the results of measurements are presented. The measured waveforms of transient thermal impedance of the examined diodes are compared with the waveforms of this parameter measured for commercially available Schottky diodes.
This paper discusses selected problems regarding a high-frequency improved current-fed quasi-Z-source inverter (iCFqZSI) designed and built with SiC power devices. At first, new, modified topology of the impedance network is presented. As the structure is derived from the series connection of two networks, the voltage stress across the SiC diodes and the inductors is reduced by a factor of two. Therefore, the SiC MOSFETs may be switched with frequencies above 100 kHz and volume and weight of the passive components is decreased. Furthermore, additional leg with two SiC MOSFETs working as a bidirectional switch is added to limit the current stress during the short-through states. In order to verify the performance of the proposed solution a 6 kVA laboratory model was designed to connect a 400 V DC source (battery) and a 3£400 V grid. According to presented simulations and experimental results high-frequency iCFqZSI is bidirectional – it may act as an inverter, but also as a rectifier. Performed measurements show correct operation at switching frequency of 100 kHz, high quality of the input and output waveforms is observed. The additional leg increases efficiency by up to 0.6% – peak value is 97.8%.
This paper presents the results of studies concerning the production and characterization of Al-SiC/W and Cu-SiC/W composite materials with a 30% volume fraction of reinforcing phase particles as well as the influence of corrosion and thermal shocks on the properties of selected metal matrix composites. Spark plasma sintering method (SPS) was applied for the purpose of producing these materials. In order to avoid the decomposition of SiC surface, SiC powder was coated with a thin tungsten layer using plasma vapour deposition (PVD) method. The obtained results were analysed by the effect of the corrosion and thermal shocks on materials density, hardness, bending strength, tribological and thermal properties. Qualitative X-ray analysis and observation of microstructure of sample surfaces after corrosion tests and thermal shocks were also conducted. The use of PVD technique allows us to obtain an evenly distributed layer of titanium with a constant thickness of 1.5 µm. It was found that adverse environmental conditions and increased temperature result in a change in the material behaviour in wear tests.
The paper presents the issue of synthetic cast iron production in the electric induction furnace exclusively on the steel scrap base. Silicon
carbide and synthetic graphite were used as carburizers. The carburizers were introduced with solid charge or added on the liquid metal
surface. The chemical analysis of the produced cast iron, the carburization efficiency and microstructure features were presented in the
paper. It was stated that ferrosilicon can be replaced by silicon carbide during the synthetic cast iron melting process. However, due to its
chemical composition (30% C and 70% Si) which causes significant silicon content in iron increase, the carbon deficit can be partly
compensated by the carburizer introduction. Moreover it was shown that the best carbon and silicon assimilation rate is obtained where the
silicon carbide is being introduced together with solid charge. When it is thrown onto liquid alloy surface the efficiency of the process is
almost two times less and the melting process lasts dozen minutes long. The microstructure of the cast iron produced with the silicon
carbide shows more bulky graphite flakes than inside the microstructure of cast iron produced on the pig iron base.
In this work, in order to obtain breakdown voltage values of the 4H-SiC p-i-n diodes above 1.7kV, three designs have been examined: single-zone junction termination extention (JTE), double-zone JTE and a structure with concentric rings outside each of the areas of the double-zone JTE (space-modulated JTE). The influence of geometry and the level of p-type doping in the JTE area as well as the charge at the interface between the p-type JTE area and the passivation layer on the diode breakdown voltage was studied. The effect of statistical dispersion of drift layer parameters (thickness, doping level) on diodes breakdown voltage with various JTE structures was investigated as well. The obtained results showed that the breakdown volatge values for a diode with single zone JTE are very sensitive both to the dose of JTE area and charge accumulated at the JTE/dielectric interface. The use of a double zone or space-modulated JTE structures allows for obtaining breakdown voltage above 1.7 kV for a much wider range of doping parameters and with better tolerance to positive charge at the JTE/dielectric interface, as well as better tolerance to statistical dispersion of active layer parameters compared to a single zone JTE structure.
Wider application of silicon carbide (SiC) is anticipated for increasing the durability of various structural facilities. For this study, SiC was fabricated with decreased electrical resistivity for precision electrical discharge machining. Two-step reaction sintering by infiltration of molten Fe-Si alloy was applied for SiC fabrication. The procedure included first sintering at 973 K in Ar gas atmosphere and second sintering by spontaneous infiltration of molten Fe-75%Si alloy at 1693 K in vacuum. The sintered structure porosity became very low, forming 3C-type SiC. Results confirmed that molten Fe-75%Si alloy infiltration occurred because of reaction sintering. The electrical resistivity of the sintered SiC infiltrated by molten Fe-75%Si alloy can be improved to be two orders of magnitude lower than that by molten Si, consequently maintaining the high performance of SiC.
The paper presents a concept of a control system for a high-frequency three-phase PWM grid-tied converter (3x400 V / 50 Hz) that performs functions of a 10-kW DC power supply with voltage range of 600÷800 V and of a reactive power compensator. Simulation tests (in PLECS) allowed proper selection of semiconductor switches between fast IGBTs and silicon carbide MOSFETs. As the main criterion minimum amount of power losses in semiconductor devices was adopted. Switching frequency of at least 40 kHz was used with the aim of minimizing size of passive filters (chokes, capacitors) both on the AC side and on the DC side. Simulation results have been confirmed in experimental studies of the PWM converter, the power factor of which (inductive and capacitive) could be regulated in range from 0.7 to 1.0 with THDi of line currents below 5% and energy efficiency of approximately 98.5%. The control system was implemented in Texas Instruments TMS320F28377S microcontroller.