Effect of precursor size on the structure and mechanical properties of calcium-stabilized sialon/cubic boron nitride nanocomposites (original) (raw)
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Spark plasma sintering of cBN/β-SiAlON composites
Materials Science and Engineering: A, 2010
cBN/-SiAlON composites with different cBN contents were fabricated by spark plasma sintering (SPS) process. The densification, thermal stability of cBN, microstructure and mechanical properties of the resultant composites were investigated. The addition of cBN particles to -SiAlON could increase the Vickers hardness, flexural strength and fracture toughness of -SiAlON. It is attributed to the high density, no obvious cBN to hBN transformation and good interface bonding between cBN grains and -SiAlON matrix.
Ceramics International, 2018
Several compositions of calcium stabilized sialon ceramics were synthesized by using nano-size starting powder precursors and spark plasma sintering technique at a relatively low temperature of 1500°C. The formation of calcium alpha/beta-sialons was investigated for the compositions represented by Ca m/2 Si 12-(m+n) Al m+n O n N 16-n where m and n values were varied from 0.6 to 1.6 and 0.4-1.6, respectively. Phase analysis of the selected compositions helped in developing the phase boundary between alpha and alpha/beta phase regimes. Effect of m and n values on the evolution of the final phase(s), densification and mechanical properties were evaluated. All samples yielded densified ceramics with density values (3.13-3.19 g/cm 3) comparable with those reported in the literature for similar compositions and synthesized at temperatures greater than 1700°C via conventional sintering techniques. Vickers hardness value HV 10 of 20 GPa was measured for the Ca 0.5 Si 10.6 Al 1.4 O 0.4 N 15.6 composition (with m = 1.0 and n = 0.4) synthesized at 1500°C. An increase in n value (higher oxide content) was observed to facilitate the formation of beta-sialon and AlN polytype phases leading to an increase in fracture toughness but a decrease in Vickers hardness.
The Property Characterization of α-Sialon/Ni Composites Synthesized by Spark Plasma Sintering
Nanomaterials
This study investigates the effect of micron-sized nickel particle additions on the microstructural, thermal, and mechanical property changes of α-sialon ceramic composites. The α-sialon/Ni composites were synthesized with an increasing amount of Ni (10–40 wt.%) using the spark plasma sintering technique and nanosized alpha precursors at a relatively low synthesis temperature of 1500 °C with a holding time of 30 min in each case. The density of the samples increased with the increase in Ni content of up to 15 wt.% and, with the further increase in Ni content, it became almost constant with a slight decrease. Furthermore, thermal conductivity and thermal expansion properties of Ni-sialon composites improved slightly with the inclusion of 10 wt.% Ni. The addition of Ni to α-sialon matrix resulted in a decrease in the hardness of the composites from HV10 21.6 to HV10 16.3, however the presence of Ni as a softer interfacial phase resulted in a substantial increase in the fracture toughn...
International Journal of Refractory Metals and Hard Materials, 2018
Calcium stabilized alpha-sialon ceramic was synthesized using spark plasma sintering (SPS). The size effect of aluminum nitride precursor (1 μm and 50 nm) on the phase analysis, microstructural and mechanical characteristics of the processed sialon was studied. Alongside the size of AlN precursor, holding time and sintering temperature were also varied in order to assess the degree of densification, phase transformation and its subsequent effect on the mechanical properties of these materials. The development of alpha phase was found to be strongly dependent on the particle size of the aluminum nitride (AlN) precursor. Interestingly, this novel approach of changing particle size from micro to nano-level combined with the SPS process resulted in the formation of alpha-sialon ceramic at much lower than previously reported sintering temperature i.e. 1500°C as compared to 1700/1800°C. Surface oxide layer associated with AlN particles resulted in the formation of additional beta phase along with major alpha phase in the final product. The sialon product synthesized from micron-size AlN particles (1 μm) at a sintering temperature of 1500°C exhibited Vickers hardness value HV 10, of 18 GPa and moderate fracture toughness of 5.6 MPa √ m. However, sialon materials synthesized from nano-size AlN particles (50 nm) showed a hardness value of 14 GPa while displaying an improved fracture toughness of 7 MPa √ m. Increase in holding time resulted in a slight increase in densification of these materials, however its influence on mechanical properties was less significant as compared to the effect of particle size of aluminum nitride staring powder precursor.
Nitrogen-rich Ca-α-SiAlON ceramics were synthesized using nanosized precursors via spark plasma sintering process for various holding times (10, 20, 30 min) at relatively low temperatures of 1500 °C and 1600 °C. The effects of the experimental conditions, namely sintering time and temperature, on the densification and mechanical properties of the processed α-SiAlON were investigated. All of the conditions yielded nearly completely densified ceramics. A remarkable combination of hardness and toughness was obtained for the samples at either sintering temperature; and these values were greatest after 30 min sintering time, with Vickers hardness values of 21.6 GPa and 20.5 GPa and fracture toughness values of 7.3 MPa√m and 9.7 MPa√m for sintering temperatures of 1500 °C and 1600 °C, respectively. The differences in the mechanical properties of these samples were related to differences in the phases formed during the sintering process.
Ceramics International, 2012
SiO 2-cBN composites were consolidated by spark plasma sintering at 1473-1973 K. The effects of cBN content and sintering temperature on the relative density, phase transformation, microstructure and mechanical properties of the SiO 2-cBN composites were investigated. The relative density of the SiO 2-cBN composites increased with increasing SiO 2 content. The phase transformation of cBN to hBN in SiO 2-cBN composites was identified at 1973 K, showing the highest transformation temperature in cBN-containing composites. The SiO 2-20 vol% cBN composites sintered at 1673 K showed the highest hardness and fracture toughness of 12.5 GPa and 1.5 MPa m 1/2 , respectively.
Development and Processing of SiAlON Nano-Ceramics by Spark Plasma Sintering
Advances in Science and Technology, 2014
The development of SiAlON-based ceramics has shown great impact in the cutting/drilling tool industry and for other engineering applications. It is highly desirable to reduce the cost of the cutting tools by increasing their service lifetime. Potential ways to improve tool life is by preparing these SiAlON-based ceramics adopting non-conventional synthesis routes and by using different precursors. The present study reports the results of synthesis of Ba-SiAlON-based nano-ceramics via the spark plasma sintering (SPS) technique. Generally, metal nitride and metal oxide precursors are used for synthesizing self-reinforced SiAlON ceramics. In this work, nanosized precursors including amorphouswere used, which could be a novel way to synthesize Ba-SiAlONs at lower temperatures with enhanced performance. The properties of these SiAlONs are tailored by optimizing the synthesis parameters. The synthesized samples were characterized by X-ray diffraction and field emission scanning electron microscopy to study the effect of processing parameters on microstructure, density and hardness.
Journal of the European Ceramic Society, 2011
In the present study, we report the effects of starting -Si 3 N 4 particle sizes and post-sintering heat treatment on microstructure evolution and mechanical properties of prepared ␣- SiAlON ceramics. Three different -Si 3 N 4 starting powders, with particle sizes of 2, 1 and 0.5 m were used to prepare ␣- SiAlON ceramics by gas-pressure sintering. Elongated -SiAlON grain morphology was identified in the samples prepared using 0.5 m particle size -Si 3 N 4 powder. Low-aspect ratio grain morphology was observed in samples prepared from starting powders with coarse particles . The sintered samples were further heat treated to develop desired microstructure with elongated grains. The hardness and indentation fracture toughness values of sintered and heat treated samples were found to lie in the range of 12.4-14.2 GPa and 5.1-6.4 MPa m 1/2 respectively. It was revealed that fracture toughness increases with decrease in particle size of starting -Si 3 N 4 powder.
Journal of Advanced Ceramics, 2020
Calcium stabilized nitrogen rich sialon ceramics having a general formula of CaxSi12-2xAl2xN16 with x value (x is the solubility of cation Ca in α-sialon structure) in the range of 0.2–2.2 for compositions lying along the Si3N4:1/2Ca3N2:3AlN line were synthesized using nano/submicron size starting powder precursors and spark plasma sintering (SPS) technique. The development of calcium stabilized nitrogen rich sialon ceramics at a significantly low sintering temperature of 1500 °C (typically reported a temperature of 1700 °C or greater) remains to be the highlight of the present study. The SPS processed sialons were characterized for their microstructure, phase and compositional analysis, and physical and mechanical properties. Furthermore, a correlation was developed between the lattice parameters and the content (x) of the alkaline metal cation in the α-sialon phase. Well-densified single-phase nitrogen rich α-sialon ceramics were achieved in the range of 0.53(3) ⩽ x ⩽ 1.27(3). A n...
Self-Reinforced Nitrogen-Rich Calcium–α-SiAlON Ceramics
2007
Nitrogen-rich Ca-a-SiAlON ceramics with nominal compositions Ca x Si 12À2x Al 2x N 16 and 0.2rxr2.6, extending along the Si 3 N 4 -1/2Ca 3 N 2 :3AlN tie line, were prepared from Si 3 N 4 , AlN, and CaH 2 precursors by hot pressing at 18001C. The x values attained were determined by energy-dispersive X-ray (EDX) microanalysis and X-ray powder diffraction (XRPD) data using the Rietveld method. The results show that Ca-a-SiAlONs form continuously within the compositional range x 5 0 to at least x 5 1.82. Phase assemblages, lattice parameters, Vickers hardness, and fracture toughness were determined and correlated to the calcium content, x. Owing to a high sintering temperature and the use of CaH 2 as a precursor, grain growth was kinetically enhanced, resulting in self-reinforced microstructures with elongated grains. The obtained Ca-a-SiAlON ceramics demonstrate a combination of both high hardness B21 GPa, and high fracture toughness B5.5 MPa . m 1/2 . P. Becher-contributing editor S.