Origin of macrostrains and microstrains in diamond-SiC nanocomposites based on the core-shell model (original) (raw)
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Microstructure of diamond–SiC nanocomposites determined by X-ray line profile analysis
Diamond and Related Materials, 2006
Diamond composites with nanosize diamond crystals and nanosize SiC matrix were obtained at 8 GPa and temperatures varied between 1800 and 2000-C. Multiple Whole Profile fitting method applied to X-ray diffractograms of sintered composites provided information on crystallite size and population of dislocations. When the temperature was increased at a constant pressure, it led to a growth of crystallite sizes in both phases and reduced population of dislocations. Porosity was limiting hardness of the specimens indicating importance of sample preparation prior to sintering nanosize diamond powders.
Structure of diamond–silicon carbide nanocomposites as a function of sintering temperature at 8GPa
Materials Science and Engineering: A, 2008
Nanosize diamond-silicon carbide composites have been sintered at high temperatures and a fixed pressure of about 8 GPa. Crystallite size, densities of stacking faults and dislocations in diamond and silicon carbide crystallites are determined by X-ray diffraction profile analysis. It has been shown that crystallite sizes increase while population of stacking faults and dislocations decrease with temperature increasing from 1820 • C to 2320 • C. These conclusions indicate that to produce composites with small residual stresses the sintering process should be conducted at the highest possible temperatures.
Journal of Materials Research, 2004
A high-pressure silicon infiltration technique was applied to sinter diamond–SiC composites with different diamond crystal sizes. Composite samples were sintered at pressure 8 GPa and temperature 2170 K. The structure of composites was studied by evaluating x-ray diffraction peak profiles using Fourier coefficients of ab initio theoretical size and strain profiles. The composite samples have pronounced nanocrystalline structure: the volume-weighted mean crystallite size is 41–106 nm for the diamond phase and 17–37 nm for the SiC phase. The decrease of diamond crystal size leads to increased dislocation density in the diamond phase, lowers average crystallite sizes in both phases, decreases composite hardness, and improves fracture toughness.
Composites Part A: Applied Science and Manufacturing, 2009
Diamond-silicon carbide composites were sintered at 10 GPa and three different temperatures: 1600, 1800, and 2000°C. Distributions of residual surface stresses in diamond crystals were obtained by the analysis of Raman band shifts and splitting. It was noted that stresses concentrate around points of contacts between diamond crystals. Average stress increase with increasing sintering temperature. Complementary information on average sizes of crystallites, concentration of stacking faults, and population of dislocations in both diamond and SiC were obtained from X-ray diffraction profile analysis. It was observed that for both diamond and silicon carbide phases the average crystallite sizes decrease. The population of dislocations in the diamond phase increases with increasing sintering temperature and the population fluctuates in the SiC phase. Concentration of stacking faults was significant only in SiC.
Synthesis of nanostructured composite material based on nanodiamonds modified by silicon
Materials Today: Proceedings, 2018
Composite nanostructured powder nanodiamond-SiC with particles of size from 0.1 to 5 μm is synthesized on the basis of nanodiamonds modified by carbon and silicon under vacuum annealing. A compact diamond composite material consisting of nanostructured grains of size 0.2-0.5 microns is formed as a result of high pressure-high temperature sintering of the powder under the pressure range of 1.0-2.5 GPa. The mechanical milling of the synthesized compacts makes it possible to obtain a polycrystalline diamond micropowder with submicron-and nanocrystalline structure with particles of size up to 50 μm.
Journal of the European Ceramic Society, 2019
Diamond/SiC composites have attracted considerable research interests due to their outstanding properties sought for a wide range of applications. Among a few techniques used for the fabrication of diamond/SiC composites, molten Si infiltration is an approach highly favored due to its cost-effectiveness and process flexibility. This study critically evaluated the interfacial zone surrounding the diamond in a reaction bonded (RB) diamond/SiC composite. XRD suggests that the composite consists of diamond, α-SiC, β-SiC, Si, and graphite. TEM reveals that a thin layer of graphite surrounds the diamond grain and it appears to form through a process of diamond graphitization and amorphous carbon transformation during the fabrication. In addition, a carbon dissolution and saturation process is proposed as a predominant mechanism for the formation of nano-crystalline SiC near the interface as well as the defects inside the SiC grits. A minor Al 4 C 3 phase is occasionally detected near the interface region.
Journal of Alloys and Compounds, 2004
The effect of the presence of surface strains on the apparent lattice parameters (alp) obtained experimentally for nanocrystalline SiC is discussed. The alp values were determined for two kinds of powders with an average crystallite size of 11 nm and related sintered samples. The measurements were done in a wide range of the diffractions vector up to Q = 12 Å −1 , allowing for evaluation of the internal pressure in the grains. Based on in situ high-temperature measurements, the thermal expansion coefficient and overall temperature factor B T were evaluated. It is shown that while the thermal expansion coefficient changes very little upon sintering, there is a large difference in the amplitude of the atomic oscillations between powders and sintered SiC reflected in a difference between respective Debye temperatures. It is concluded that the overall thermal properties of nanocrystals are determined by two components: thermal properties of the crystallite surface and its interior. The atoms at the surface vibrate much stronger than those in the bulk, and their behavior is strongly affected by the crystallite's environment.
Journal of Materials Research, 2007
Microstructure of sintered nanocrystalline SiC is studied by x-ray line profile analysis and transmission electron microscopy. The lattice defect structure and the crystallite size are determined as a function of pressure between 2 and 5.5 GPa for different sintering temperatures in the range from 1400 to 1800°C. At a constant sintering temperature, the increase of pressure promotes crystallite growth. At 1800°C when the pressure reaches 8 GPa, the increase of the crystallite size is impeded. The grain growth during sintering is accompanied by a decrease in the population of planar faults and an increase in the density of dislocations. A critical crystallite size above which dislocations are more abundant than planar defects is suggested.
Materials transactions, 2022
This study reports on an interfacial design method of CuSiC composites by means of nano-diamond/SiC composite particles in meltinfiltration process. In the case of CuSiC composites fabricated by melt-infiltration process, reaction layers consisting of spherical carbon particles and CuSi solid-solution alloys were observed as SiC particles reacted with melt Cu. Formation of reaction layers is not appropriate to obtain the predesigned characteristics such as physical and mechanical properties of the CuSiC composites. To overcome this problem, nanodiamonds, which were chemically inert with Cu, were bonded to the surfaces of SiC particles by amorphous silica as a bond material in order to shield the SiC particles from reacting with melt Cu. It was found that this shielding method enabled us to disperse SiC particles homogeneously in the Cu matrix without reaction layers. This interfacial design based on the composite particles should be expected to be applied to a promising mass production technology of metal-matrix composites (MMCs) due to its short processing time and large amount of production for processing composite particles.
Nano-diamond reinforced ZrB2–SiC composites
Ceramics International, 2020
The effect of adding various amounts of nano-diamond additive (0, 1, 2, and 3 wt%) on the densification behavior and mechanical properties of ZrB 2-25 vol% SiC samples were investigated in this research. All samples were spark plasma sintered at 1900°C under 40 MPa external pressure for 7 min. Relative density (RD) values higher than 99.9% were obtained for the samples with 0, 1, and 2 wt% nano-diamond, while adding 3 wt% diamond dropped the RD by~1.2%. The XRD and microstructural evaluations revealed the formation of some in-situ phases, namely ZrC and B 4 C. The highest Vickers hardness (24.7 GPa) and fracture toughness (5.8 MPa m 1/2) were achieved for the samples doped with 2 and 3 wt% nano-diamond, respectively. Ultimately, the SEM micrographs indicated the role of different toughening mechanisms on obtaining such a high value of fracture toughness.