Influence of Processing on the Microstructural Development and Flexure Strength of Al,O,/SiC Nanocomposites (original) (raw)
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Materials & Design, 2012
In this study Al 2 O 3-SiC micro/nanocomposites have been fabricated by mixing alumina nanopowders and silicon carbide micro/nanopowders, followed by hot pressing at 1550, 1600, 1650 and 1700°C. The density, mechanical properties and fracture mode of Al 2 O 3-SiC composites containing different volume fractions (2.5%, 5%, 7.5%, 10% and 15%) of micro/nanoscale SiC particles were investigated and compared with those of alumina. The relative density of composites could reach values very close to theoretical density, especially after sintering at 1700°C. However, relative density declined by increasing the SiC fraction at the same sintering temperature. The flexural strength of composites was best for sintering temperature of 1700°C and showed a maximum of 545 MPa for Alumina-10%SiC sintered at 1700°C. Hardness showed a remarkable increase by adding SiC and reached a pick of 22.6 GPa for Alumina-15%SiC. Fracture toughness and fracture mode of alumina and composites with 5%, 10% and 15% SiC sintered at 1700°C were also investigated. Composites were tougher than alumina and the scanning electron microscopy observations showed that fracture mode changes from intergranular for alumina to transgranular for composites. Finally X-ray diffraction analysis could not detect any chemical reactions between Al 2 O 3 and SiC particles.
Journal of Composite Materials, 2010
Al(1, 3, 5, 7, 10 vol%) SiC nanocomposites were produced by mechanical alloying (MA) and double pressing/sintering route. The characteristics of the milled powders and the consolidate specimens were examined using high resolution scanning electron microscopy and X-ray diffraction method. Compression and hardness tests were used to study the effect of SiC volume fraction on the strength of AlSiC nanocomposites. It was shown that with increasing the SiC volume fraction, finer particles with narrower size distribution and smaller crystallite size are obtained after MA. During sintering close to the melting point of aluminum, the presence of nanometer-scaled SiC particles was found to hinder the grain growth significantly. The Al matrix with a higher SiC content exhibited more potential for grain boundary pinning, i.e., smaller grain size was obtained at higher SiC volume fractions. Consequently, an improved mechanical strength was obtained. The processing method (MA/pressing/sintering) can be used for fabrication of near-net shape Al matrix nanocomposites.
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.
Fabrication and mechanical properties of nano-/micro-sized Al2O3/SiC composites
Materials Science and Engineering: A, 2009
The processing and mechanical behavior of Al 2 O 3 composites with 1-20 wt.% nano-/micro-sized SiC particles was investigated. The composites were densified by hot-pressing. The mechanical properties of nano-/micro-sized SiC/Al 2 O 3 composites including hardness, fracture toughness and flexural strength were investigated. It was found that the fracture strength and fracture toughness of the nano-/micro-sized SiC/Al 2 O 3 composites were significantly improved in comparison with the monolithic Al 2 O 3. 7.6 MPa m 1/2 was the highest fracture toughness and was found in the composite with 5% SiC, while the 20% SiC composite exhibited the highest flexural strength. The toughening and strengthening mechanisms of the ceramic composites were discussed.
Study of Mechanical Properties and Fracture Mode of Alumina-Silicon Carbide Nanocomposites
International Journal of Modern Physics: Conference Series, 2012
In this study Al 2 O 3- SiC nanocomposites have been fabricated by mixing of alumina and silicon carbide nano powders, followed by hot pressing at 1700°C. The mechanical properties and fracture mode of Al 2 O 3- SiC nanocomposites containing different volume fractions (5, 10 and 15%) of nano scale SiC particles were investigated and compared with those of alumina. Al 2 O 3- SiC powders were prepared by planetary milling in isopropanol. Fracture mode of specimens was investigated by means of scanning electron microscopy. Nanocomposites were tougher than alumina when they were hot pressed at the same temperature, and the values of nanocomposite's flexural strength and hardness were higher than those of alumina. Flexural strength, hardness and fracture toughness of the nanocomposites increase by increasing the volume percent of SiC up to 10% and then decrease slightly. The Scanning electron microscopy observations showed that fracture mode changes from intergranular for alumina to ...
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...
In the present study, pulse echo overlap method (PEO) has been used as a non-destructive technique for evaluating the mechanical properties of Al/SiC nanocomposites. The nano-sized AI/SiC powders were prepared by mechanical alloying method. The particle size and microstructures of the milled powders were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) techniques. Al/SiC powders containing different amounts of nano-size SiC particles (0, 5 and 10 vol.%) were subsequently cold-pressed and sintered to produce bulk composite samples. The polycrystalline bulk modulus K, Young's modulus E, shear modulus G, Poisson ratio t and hardness H of Al/SiC composites are gained by PEO method. The results showed an increase in the hardness value from 3.8 to 6.6 GPa and a decrease in Al crystallite size from 175.6 to 90.8 nm with increasing SiC content. Besides, Young's modulus of Al/10SiC sample was measured to be 97.1 GPa, which is much higher than that for pure Al (72.6 GPa). Poisson's ratio results indicate that its value decreases with increasing the elastic moduli and ultrasonic wave velocities of Al/SiC composites. The Pugh ratio showed the ductility behavior of all Al/SiC samples, while Poisson's ratio showed slightly decrease in the ionic contribution with increasing the volume fraction of SiC nanoparticles in metal matrix composites MMCs. Microstructural analysis revealed that the origin of change in mechanical properties is attributed to the decrease in interparticle spacing and increase in the grain boundary area, which provides more obstacles for dislocation pile up in the adjacent grains.
Journal of the Korean Ceramic Society, 2019
In this research, some mechanical properties of Al 2 O 3-based composites containing nanoSiC and nanoMgO additives, including elasticity modulus, hardness, and fracture toughness, have been evaluated. Micron-sized Al 2 O 3 powders containing 0.08 wt.% nanoMgO particles have been mixed with different volume fractions of nanoSiC particles (2.5 to 15 vol.%). Untreated samples have been sintered by using hot-press technique at temperatures of 1600 to 1750°C. The results show significant increases in the mechanical characteristics with increases in the sintering temperature and amount of nanoSiC particles, with the result that the elasticity modulus, hardness, and fracture toughness were obtained as 426 GPa, 21 GPa, and 4.5 MPa.m 1/2 , respectively.
Silicon carbide particle size effects in alumina-based nanocomposites
Acta Materialia, 1996
AhOJSiC nanocomposites with a systematic variation in their SIC particle size together with monolithic alumina were produced using conventional powder processing, polymer pyrolysis and hot-pressing. The microstructures of the materials were investigated by means of transmission and scanning electron microscopy and correlated to their mechanical properties. All nanocomposites showed a clear increase in strength over similar grain size alumina but no clear dependence on the size of the Sic nano-reinforcement. However, the fracture toughness of the nanocomposites seems to increase with the Sic particle size but with values little changed from the toughness of monolithic alumina as measured by the Vickers indentation technique. The surface and bulk flaw populations were characterised using a Hertzian indentation technique and a Griffith flaw size analysis of strength data. The investigations revealed a significant difference between the monolithic alumina and nanocomposites. The strength increase in the nanocomposites is explained by the observed decrease in both the surface and processing flaw sizes, which further decreased with decreasing Sic particle size. CopJlright 0 1996 Acta Metallurgica Inc.