Sinter-HIP of polymer-derived Al2O3–SiC composites with high SiC contents (original) (raw)
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Al2O3–SiC composites prepared by infiltration of pre-sintered alumina with a poly(allyl)carbosilane
Journal of the European Ceramic Society, 2011
The Al 2 O 3 /SiC nanocomposites containing 3-8 vol.% SiC were prepared through infiltration and in situ thermal decomposition of a preceramic polymer SiC precursor (poly(allyl)carbosilane) in pre-sintered alumina matrix. The volume fraction of SiC, and the microstructure of composites were adjusted by concentration of the polymer solution, and by the conditions of pyrolysis and sintering. The specimens were densified by pressureless sintering at temperatures between 1550 and 1850 • C in flowing argon. The use of powder bed producing SiO, CO and other volatile species suppressed decomposition reactions in the composites and was vital for their successful densification. The experimental results are discussed against thermodynamic analysis of the system Al 2 O 3 /SiC/SiO 2 in an inert Ar atmosphere.
Sintering Atmosphere Effects on the Densification of Al-SiC Compacts
2014
The influence of SiC powder addition on densification of Al-SiC compacts during sintering in different atmospheres was investigated. It was performed in a dilatometer in flowing nitrogen, nitrogen/hydrogen (95/5 by volume) and argon. Fine, F500 grade of SiC powder was used. Mixtures containing 10 and 30 vol.% of SiC reinforcement were prepared in a Turbula mixer. Green compacts of about 82% of theoretical density were made of each mixture. For comparison, compacts made of pure aluminum powder were also investigated. It was shown that nitrogen is the best sintering atmosphere because only in this atmosphere did shrinkage take place. Its amount is lowered by ceramic powder addition, i.e. the more SiC the less densification occurs. Additionally, the formation of clusters enhanced in compacts containing 30 vol.% SiC, is also responsible for limiting the shrinkage. Microstructural examinations of sintered composites revealed that sintering of compacts occurs in the presence of the liquid...
Synthesis and Characterization of Al–SiC Nanocomposites Produced by Mechanical Milling and Sintering
Advanced Composite Materials, 2011
Aluminum powder and various volume fractions of SiC particles with an average diameter of 50 nm were milled by a high-energy planetary ball mill to produce nanocrystalline Al-SiC nanocomposite powders. Double pressing/sintering process was used to consolidate powders to cylindrical specimens. It was shown that a double cycle of cold pressing and sintering can be utilized to obtain high density Al-SiC nanocomposite parts without using a hot-working step. High resolution scanning electron microscopy (HRSEM), X-ray diffraction (XRD) and laser particle size analyzer (PSA) were used to study the morphological and microstructural evolution of nanocomposite powders and bulk samples. The role of volume fraction of SiC nanoparticles in grain size of both as-milled and as-consolidated aluminum matrix was investigated. It was found that the presence of the higher SiC particles eventuate to slowly decrease in grain size of aluminum matrix powders. However, this trend is strongly noticeable in grain size of consolidated samples. The pinning effects on grain stability by SiC nanoparticles were quantitatively analyzed. It was found that Gladman's model is in close agreement with the experimentally determined grain size of Al-SiC nanocomposites.
Production of Al2O3-SiC composites from micrometer α-Al2O3 powder obtained via sol-gel
Revista Mexicana de Física
Alumina (Al2O3) is an advanced ceramic material developed for different applications as refractories, precision tools, pacemaker, etc. Solid state sintering of alumina or matrix ceramic composites (CMCs) compacts starts from powders. Once method to produce high quality aluminum oxide powders is the sol-gel technique. Alumina begins as pseudo-crystallized aluminum hydroxide gel which is produced under moderate reaction conditions trough a colloidal suspension. In this work, Al2O3 powder was produced by precipitation of pseudoboehmite (PB) through sol-gel process. Subsequently, a mixture of Al2O3/SiC powders with 5 wt.% of SiC as reinforcement was produced. This mixture was used to manufacture green compacts by uniaxial pressing at 440 MPa. Afterward, some samples were applied a heat treatment (pre-sintered) at 1200°C for 6 h in air. Sintering was carried out in a vertical dilatometer Linseis L75 V up to 1500°C for 2h under argon atmosphere. Pseudobohemite, alumina powders and Al2O3/S...
Nanoscale composites based on Al2O3 and SiC prepared by electroconsolidation method
19th International Scientific Conference Engineering for Rural Development Proceedings
In the paper, preparation and characteristics of nanoscale composites based on mixtures of Al 2 O 3 with additions of SiC up to 50 wt % are described. In the experiments, electroconsolidation of powdered ceramic materials was performed in different proportions at temperatures between T sint = 1400 and 1800 ºC during 2, 3 or 4 minutes. The sintered samples were analyzed in the terms of grain growth, grain dispersion and material densification related to the sintering parameters (time and temperature) and proportion of powders. One of the most important findings was that the nanodispersed SiC supported better densification. It was demonstrated that the prolonged sintering time caused decrease of small dispersed particles, while larger particles increased in number. The obtained density of sintered material was higher than that recently reported, but achieved at substantially lower energy consumption and cheaper equipment.
International Journal of Applied Ceramic Technology, 2019
The hot pressing process of monolithic Al2O3 and Al2O3‐SiC composites with 0‐25 wt% of submicrometer silicon carbide was done in this paper. The presence of SiC particles prohibited the grain growth of the Al2O3 matrix during sintering at the temperatures of 1450°C and 1550°C for 1 h and under the pressure of 30 MPa in vacuum. The effect of SiC reinforcement on the mechanical properties of composite specimens like fracture toughness, flexural strength, and hardness was discussed. The results showed that the maximum values of fracture toughness (5.9 ± 0.5 MPa.m1/2) and hardness (20.8 ± 0.4 GPa) were obtained for the Al2O3‐5 wt% SiC composite specimens. The significant improvement in fracture toughness of composite specimens in comparison with the monolithic alumina (3.1 ± 0.4 MPa.m1/2) could be attributed to crack deflection as one of the toughening mechanisms with regard to the presence of SiC particles. In addition, the flexural strength was improved by increasing SiC value up to 2...
Powder Metallurgy, 2013
Al based alloys reinforced with different amounts (5, 12 and 20 wt-%) of nanosized SiC particulates were synthesised by mechanical alloying and consolidated by the spark plasma sintering (SPS) technique. The distribution of the reinforcement phase in the composite was evaluated as a function of the milling time and the amount of SiC. The processed materials were characterised by scanning electron microscopy and energy dispersive spectroscopy for the morphology and composition and X-ray diffraction. Continuous reduction in crystallite size was observed as milling progressed and after milling for 20 h the resulting powders reached a grain size of ,100 nm. These Al-SiC composites were successfully consolidated by the SPS method at different sintering temperatures of 400, 450 and 500uC. It is suggested that a higher hardness can be achieved even at 20 wt-%SiC when a higher sintering temperature, for example, above 500uC, is used.
Journal of The European Ceramic Society, 2007
Al 2 O 3 -SiC nanocomposites containing 3-8 vol.% SiC were prepared from fine ␣-alumina powder and a poly(allyl)carbosilane precursor of SiC by polymer infiltration of porous alumina matrix (composites IP), or by warm pressing of polymer-coated alumina powder (composites CW). The polymer was converted to SiC by careful heating of green specimens in inert atmosphere (Ar). The residual porosity was eliminated to less than 10% by pressureless sintering (PS) at temperatures between 1700 and 1850 • C. The post-sintering hot isostatic pressing (HIP) at 1700 • C eliminated the residual porosity to less than 1%, but also resulted in coarsening of the alumina matrix grains, and the inter-and intragranular SiC inclusions. The Vickers hardness of IP specimens sintered at T < 1850 • C increased by 1-10%, which is attributed to elimination of residual porosity. The hardness and indentation fracture toughness of specimens IP sintered at 1850 • C decreased after HIP by 6 and 15%, respectively. The HIP of CW composites increased their hardness and fracture toughness by approximately 10%. The maximum fracture toughness of 5.2 ± 0.2 MPa m 1/2 was measured for the materials containing 8 vol.% of SiC. A correlation was found between the fracture toughness, and the mean size and volume fraction of intergranular SiC inclusions in composites CW.