Silicon nitride based nanocomposites produced by two different sintering methods (original) (raw)
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Ceramics International, 2010
Multi-walled carbon nanotube (MWCNT) reinforced silicon nitride composites have been prepared by hot isostatic pressing at 20 MPa and gas pressure sintering at 2 MPa. To assure a good dispersion of the MWCNTs a highly efficient attritor milling was employed in the preparation process of the powder mixtures. The morphological and micro-structural evolution of the powder particles during the high-energy milling was monitored.
Development of CNT/Si 3N 4 composites with improved mechanical and electrical properties
Composites Part B-engineering, 2006
Silicon nitride based composites with different amount (1, 3 or 5 wt%) of carbon nanotubes have been prepared by using hot isostatic pressing. Composites with 1, 5 or 10 wt% carbon black and graphite have been manufactured, in comparison. Optimisation of the manufacturing processes has been performed, providing intact carbon nanotubes during high temperature sintering. In the case of 1 or 3 wt% carbon nanotube addition, the increase of gas pressure during sintering resulted in an increase of bending strength. It was found that microstructure features achieved by properly designed sintering parameters are the main responsible factors for the strength improvements. Scanning electron microscopy showed that carbon nanotubes have a good contact to the surface of silicon nitride grains. The electrical properties of silicon nitride matrices with carbon addition may change essentially.
Properties of MWCNTs added Si3N4 composites processed from oxidized silicon nitride powders
Processing and Application of Ceramics, 2020
Si 3 N 4 /3 wt.% multi-walled carbon nanotubes (MWCNTs) composites were prepared from oxidized α-Si 3 N 4 powders and sintering additives by hot isostatic pressing (HIP). The Si 3 N 4 powders were oxidized at 1000°C in ambient air environment for 10 and 20 h and the powder mixture was sintered at 1700°C for 3 h under the pressure of 20 MPa in nitrogen. The relationship between oxidation, microstructure, tribology and mechanical properties was studied. The dispersion of MWCNTs was not optimal, as they were found mainly in the form of bundles between the β-Si 3 N 4 grains. Neither Si 2 N 2 O nor other oxide phase were observed after the sintering. This was probably caused by the presence of MWCNTs at the grain boundaries of the Si 3 N 4 grains causing reduction of oxide phases. The density, hardness, bending strengths and friction coefficient of the composites increased with the oxidation time of the Si 3 N 4 powder.
Materials
In this overview, the results published to date concerning the development, processing, microstructure characteristics, and properties of silicon nitride/carbon nanotube (Si3N4 + CNTs) composites are summarized. The influence of the different processing routes on the microstructure development of the Si3N4 + CNTs is discussed. The effects of the CNTs addition on the mechanical properties—hardness, bending strength and fracture toughness—and tribological characteristics—wear rate and coefficient of friction—are summarized. The characteristic defects, fracture origins, toughening and damage mechanisms occurring during the testing are described. The influence of the CNTs’ addition on the thermal and functional properties of the composites is discussed as well. New trends in the development of these composites with significant potential for future applications are outlined.
Development of CNT-Silicon Nitrides with Improved Mechanical and Electrical Properties
Advances in Science and Technology, 2006
This work is focusing on exploring preparing processes to tailor the microstructure of carbon nanotube (CNT) reinforced silicon nitride-based ceramic composites. Samples with different porosity's and different amount (1, 3 or 5 wt%) of carbon nanotubes have been prepared by using gas pressure sintering or hot isostatic pressing. In comparison, composites with 1wt%, 5wt% or 10wt% carbon black and graphite have been manufactured. We measured the room temperature mechanical and electrical properties, examined the micro and nano structure by X-ray diffraction and electron microscopy. It was found that it is possible to develop CNT-silicon nitride composite for applications where a decent electric conductivity and good mechanical properties are required.
Synthesis of "in situ" reinforced silicon nitride composites
Journal of the Serbian Chemical Society, 2004
The objective of this work was to investigate the effect of two different sintering additives (CeO 2 and Y 2 O 3 + Al 2 O 3 ), sintering time and amount of -Si 3 N 4 seeds on densification, mechanical properties and microstructure of self-reinforced Si 3 N 4 based composites obtained by pressureless sintering. Preparation of -Si 3 N 4 seeds, obtained also, by pressureless sintering procedure was described. Samples without seeds were prepared for comparison. The results imply that self-reinforced silicon nitride based composites with densities that are close to theoretical values and with fracture toughness of 9.3 MPa·m 1/2 can be obtained using presureless sintering procedure.
Manufacture and examination of C/Si3N4 nanocomposites
Journal of the European Ceramic Society, 2004
C/Si 3 N 4 nanocomposites have been prepared through carbon black nanograins, graphite micrograins addition to silicon nitride starting powder. The role of excess oxygen was examined by oxidising the alpha silicon nitride starting powder. For nanocomposite processing sinter-HIP and hot press have been applied. Bending strength and elastic modulus have been found to be influenced by amount of carbon black and graphite introduced in silicon nitride matrix. In the case of HIP samples a desintering process was observed. During pressure-less sintering step the structure retained the a-Si 3 N 4 phase, after second sintering step new phase(s) appeared. Hot pressed samples with a higher a-Si 3 N 4 phase contribution showed considerable improvement of hardness. #
Size Effects in Micro- and Nanocarbon Added C/Si3N4 Composite Prepared by Hot Pressing
Key Engineering Materials, 2005
Silicon nitride based composites have been fabricated by carbon addition. Carbon black nanograins and graphite micrograins were used as second phase additions. Alumina and yttria were used as sintering aids. Mixing of powders was performed in a ball mill and for comparison in a high efficient attritor mill. For sintering the hot pressing technique has been applied. Experiments at 2 MPa uniaxial pressure have been performed. The Si/N mass fraction after sintering were determined by prompt gamma activation analysis (PGAA). The amount of carbon black and graphite introduced in the silicon nitride matrix increased the porosity and decreased the hardness and bending strength of composites. Lower modulus, and lower strength was obtained for composites with carbon black addition in comparison to graphite added samples. The microstructure of composites consisted mainly of alpha and beta silicon nitride. The formation of silicon carbide was observed only at 10 wt% carbon black addition.
Metallurgical and Materials Transactions A, 2015
Graphite particle (GP)-reinforced silicon nitride (Si 3 N 4) composites were fabricated using pressureless sintering (PLS) and spark plasma sintering (SPS) in the presence of Y 2 O 3-AlN-SiO 2 ternary system. Different densification behaviors of the specimens fabricated by PLS and SPS were observed. While increasing GP content drastically reduced matrix densification during PLS at 2023 K (1750°C) with 2 hours dwell, SPS at 1923 K (1650°C) for only 10 minute under 50 MPa pressure resulted in much dense composites even up to 3.5 wt pct GP loading. Mechanical and tribological characterizations revealed that SPS-ed composites can offer improved performance compared to pure Si 3 N 4. SPS-ed 1.5 wt pct GP/Si 3 N 4 composite offered the highest resistance to wear up to 20 N normal load. Wear rate (W R) of that composite reduced bỹ 24 pct than that obtained for pure Si 3 N 4 (W R % 1.14 9 10 À3 mm 3 /N m). Furthermore, W R of SPS-ed 2.5 wt pct GP/Si 3 N 4 composite at F N = 10 to 20 N was found to be only~1/8th of W R values of PLS-ed 2.5 wt pct GP/Si 3 N 4 composite (10N W R % 6.61 9 10 À3 mm 3 /Nm; 20N W R % 9.45 9 10 À3 mm 3 /Nm). Present study indicated promising opportunity of SPS for fabricating improved Si 3 N 4 composites through GP addition. The reinforcing particles not only rendered its self-lubrication effect to SPS consolidated composites but also significantly promoted the rate of matrix densification during SPS cycle by the virtue of its high thermal and electrical conducting nature.
Ceramics International, 2012
Silicon nitride based nanocomposites have been prepared with different amount (1 and 3 wt%) of multilayer graphene (MLG) as well as exfoliated graphite nanoplatelets (xGnP) and nano graphene platelets (Angstron) in comparison. The microstructure and mechanical properties of the graphene reinforced silicon nitride based composite materials have been investigated. Homogeneous distribution of the MLG additives have been observed on the fracture surface of the sintered material. The scanning electron microscopy examinations showed that graphene platelets are inducing porosity in matrix. The bending strength and elastic modulus of MLG/Si 3 N 4 composites showed enhanced values compared to the other graphene added silicon nitride ceramic composites. These observations may be explained by the different type and quality of the starting materials and by the dispersion grade of graphene platelets having direct impact to the resulting density of the sintered samples.