Spark Plasma Sintering of SiAlON Ceramics Synthesized via Various Cations Charge Stabilizers and Their Effect on Thermal and Mechanical Characteristics

Abstract

Oxygen-rich SiAlON ceramics doped with various nanosized metal oxide (MO) stabilizers were synthesized with a view to examine their effect on thermal and mechanical characteristics. The nanosized starting powder precursors comprising Si3N4, AlN, Al2O3, and SiO2 along with oxides of Ba, Y, Mg, La, Nd, Eu, Dy, Er, and Yb as the MO charge stabilizer were employed in developing different SiAlON samples. Ultrasonic probe sonication was utilized to develop a homogenous mixture of initial powder precursors followed by spark plasma sintering (SPS) of the samples at the low temperature of 1500 °C coupled with 30 min of isothermal treatment. Sample compositions (according to general formula of alpha SiAlON: Mm/vv+Si12−(m+n)Alm+nOnN16−n) selected in the present study are represented by m value of 1.1 and n value of 1.6. The synthesized samples were evaluated for their physical behavior, microstructural and crystal structure evolution, and thermal and mechanical characteristics. More specifically, the sintered ceramics were examined by X-ray diffraction and electron microscopy to comprehend and relate the structural characteristics with the densification, thermal conductivity, hardness, and fracture toughness. The high reactivity of the nanopowders and the localized heating provided by SPS resulted in densified ceramics with relative densities in the range of 92–96%. Vickers hardness values were found to be in the range of 12.4–17.0 GPa and were seen to be profoundly influenced by the grain size of the alpha SiAlON (primary) phase. The fracture toughness of the samples was measured to be in the range of 4.1–6.2 MPa·m1/2. SiAlON samples synthesized using Er and Yb charge stabilizers were found to have the highest fracture toughness of 5.7 and 6.2 MPa·m1/2, primarily due to the relatively higher content of the elongated beta phase. While there was no obvious relationship between the thermal conductivity and the alpha SiAlON metal charge stabilizers, the values were seen to be influenced by the grain size of alpha phase where Dy-SiAlON had the lowest thermal conductivity of 5.79 W/m⋅K and Er-SiAlON showed the highest value of thermal conductivity (6.91 W/m⋅K). It was concluded that scientifically selected metal oxide charge stabilizers are beneficial in developing SiAlON ceramics with properties tailored according to specific applications.

Mechanism of improving the mechanical properties of Si3N4/TiC ceramic tool materials prepared by spark plasma sintering

“…In the sintering process, Al and O atoms in the sintering additives will also combine with some Si and N atoms in the liquid phase to synthesize Sialon structure 37 . Similar to β‐Si 3 N 4 , β‐Sialon also has elongated grains, which can improve the mechanical properties of materials 38 …”

“…37 Similar to β-Si 3 N 4 , β-Sialon also has elongated grains, which can improve the mechanical properties of materials. 38 Figure 8B shows the XRD pattern of the tool material after sintering. It can be seen that the phases of the material are β-Si 3 N 4 , TiC 0.7 N 0.3 , SiC, and α-Si 3 N 4 , there are no other impurity phases, and no peak of TiC is found.…”

Influence of the Addition of Sialon and Aluminum Nitride Fillers on the Photocuring Process of Polymer Coatings

“…Sialon is an excellent oxy-nitride ceramic due to its unique combination of high Youngs modulus (270-275 GPa), moderate hardness (15)(16)(17) and high fracture toughness (6)(7)(8) [1]. Most related work focuses on the synthesis and optimization of experimental conditions for the synthesis of various Sialon materials [1][2][3][4]. Researchers have used many additives to achieve desirable physical, thermal, mechanical and wear-resistant characteristics of Sialon-based materials [2,[5][6][7].…”