This paper describes the process of obtaining Cu-SiC-Cu systems by way of spark plasma sintering. A monocrystalline form of silicon carbide (6H-SiC type) was applied in the experiment. Additionally, silicon carbide samples were covered with a layer of tungsten and molybdenum using chemical vapour deposition (CVD) technique. Microstructural examinations and thermal properties measurements were performed. A special attention was put to the metal-ceramic interface. During annealing at a high temperature, copper reacts with silicon carbide. To prevent the decomposition of silicon carbide two types of coating (tungsten and molybdenum) were applied. The effect of covering SiC with the aforementioned elements on the composite’s thermal conductivity was analyzed. Results were compared with the numerical modelling of heat transfer in Cu-SiC-Cu systems. Certain possible reasons behind differences in measurements and modelling results were discussed.
Celem pracy było zbadanie wpływu dodatku renu na właściwości termomechaniczne i użytkowe kompozytów Cr-Al2O3 wytwarzanych metodą spiekania pod ciśnieniem w prasie HP oraz metodą Spark Plasma Sintering (SPS). Uzyskano kompozyty o gęstości przekraczającej 98 % gęstości teoretycznej. Właściwości mechaniczne (m.in. moduł Younga, wytrzymałość na zginanie, twardość, odporność na pękanie, granica plastyczności) oraz odporność na utlenianie wytworzonych materiałów są obiecujące. Zbudowano model numeryczny do obliczeń wielkości naprężeń resztkowych obecnych w materiałach faz kompozytu po procesie spiekania oraz modułów sprężystości. Wykorzystano w tym celu obrazy rzeczywistej mikrostruktury kompozytu otrzymane z tomografii komputerowej. Uzyskano dobrą zgodność wyników modelu z wynikami pomiarów naprężeń metodą XRD. Przedstawiono ponadto porównanie wyników obliczeń numerycznych i pomiarów modułu Younga przy zastosowaniu różnych metod.
EN
Chromium matrix composites reinforced with alumina ceramic particles exhibit good resistance to high temperatures are thermal shocks. They have enhanced mechanical strength in elevated temperatures, high hardness, oxidation resistance and wear resistance. These exceptional properties make them good candidates for structural applications in automotive, aerospace and energy sectors, such as elements of combustion engines, coatings in aeroengines exhaust systems, or furnace linings. The objective of the present paper is to investigate the effect of rhenium addition on the thermomechanical and service properties of chromium-alumina composites manufactured by powder metallurgy methods. A working hypothesis was made that rhenium, owing to its excellent thermomechanical properties, would enhance the properties of the chromium matrix and, thus, improve the overall performance of the composite. The Cr/Al2O3/Re composites were processed by hot pressing (HP) and by spark plasma sintering (SPS) techniques. Different sizes of chromium powders were used, the addition of rhenium was 2 vol % and 5 vol %. The sintering process was conducted at 1400-1450 °C under pressure of 30-35 MPa in inert gas atmosphere (argon). The density of the sintered composites exceeded 98 % of the theoretical density. The mechanical properties (Young’s modulus, bending strength, hardness, plastic limit) are promising. For example, the compressive strength of the composite was twice as much as that of the sintered pure chromium. The oxidation and corrosion resistance of the composites were also examined and good results were reported. A numerical FE model was developed for the prediction of thermal residual stresses generated in the phase materials after cooling. The model uses micro-CT images of the real material microstructure as the input data. A good agreement of the simulation results and the measurements by X-ray diffraction method was achieved. Young’s modulus of the obtained materials was measured by different methods (mechanical, resonance and ultrasonic) and compared with the developed micro-CT based numerical model. The obtained Cr/Al2O3/Re composites are now being tested as demonstrators of some structural elements in automotive and energy applications.
This is a review paper on the existing approaches to modelling of discrete cracks (fracture) and diffuse microcracking (damage) in ceramic matrix composites under mechanical or thermal loading. The focus is on Ceramic Matrix Composites (CMC) with metal particle inclusions and on interpenetrating metal ceramic networks. The second phase in form of ceramic inclusions is not considered. The models of toughening mechanisms are discussed in considerable detail. Sections 2-5 deal with discrete cracks while Sections 6-9 with diffuse microcracking. The paper is concluded with identification of unresolved problems and topics for future research in the area of fracture and damage of CMC.
PL
Niniejsza praca stanowi przegląd istniejących modeli pękania i uszkodzenia w kompozytach o matrycy ceramicznej (CMC) pod działaniem obciążeń mechanicznych lub termicznych. Nacisk położono na CMC z inkluzjami metalicznymi oraz na CMC typu przenikających się faz metaliczno ceramicznych. Sytuacje, gdy druga faz ma postać inkluzji ceramicznych, nie były analizowane. Rozdziały 2-5 dotyczą problemów pękania (wzrostu makroszczeliny), podczas gdy rozdziały 6-9 - problemów uszkodzenia (wpływu mikroszczeliny na zachowanie się CMC). Na zakończenie pracy zaproponowano listę nierozwiązanych problemów oraz tematów przyszłych badań pożądanych w zakresie pękania i uszkodzenia CMC.
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