Sialon Ceramics Prepared by Using CaH₂ as a Sintering Additive

Abstract

In developing elongated α‐sialon grains, a nitrogen‐rich liquid phase sintering method was introduced by using CaH2 as a sintering aid, so as to vary the N/O ratio of the liquid phase formed in the sintering process while keeping the Si/Al ratios constant. With increasing addition the phase contents changed from single β‐sialon to dual β/α‐sialons and to single Ca‐α‐sialon. At low N/O ratios the microstructures contained mainly equiaxed β‐sialon grains, and at high N/O ratios well faceted elongated Ca‐α‐sialon grains. The improved toughness (KIC=7.8 MPa·m1/2) and hardness (HV10=17.5 GPa) properties can be attributed to the formation of interlocked microstructures. High‐temperature compressive deformation tests indicated that the deformation onset temperature is determined mainly by the Si/Al and N/O ratios, whereas the deformation rate is affected by the microstructure, i.e., the morphology and amounts of elongated α‐sialon grains and residual glass phase, especially for the sialons with low N/O ratios.

Preparation, Microstructure, and Mechanical Properties of Spinel-Corundum-Sialon Composite Materials from Waste Fly Ash and Aluminum Dross

“…The reaction pathway for the formation of Sialon could be through route 1, that is, ((1) + (3) + (5) + (7)), and/or route 2, that is, (11). The -Sialon product was surrounded by glassy phase (Figure 4(c)), and its formation might occur in a liquid phase via solutiondiffusion-nucleation-reprecipitation, as previously reported by Cai et al [31].…”

Novel Sialon‐Based Ceramics Toughened by Ferro‐Molybdenum Alloy

“…However, the toughness of Sialon ceramics needs to be enhanced to improve their performance in various structural applications. Although toughness of 5.50-13.30 MPa·m 1/2 has been obtained by using in situ-formed elongated crystals, ceramic particles, or fibers as toughening agents, [6][7][8][9][10][11][12][13][14][15][16] the sintering temperature required is usually over 1700°C. [8][9][10][11][12][13] This means that more energy is consumed during the processing of Sialon ceramics under such high temperatures.…”

High-Temperature Mechanical Spectroscopy of Nitrogen-Rich Ca-α-SiAlON Ceramics

“…Pellets of the mixtures, compacted using a steel die, were hot pressed in BN‐coated graphite dies in nitrogen atmosphere in a graphite‐resistance furnace at 2073 K for 4 h under 35 MPa uniaxial pressure. Details of the sintering process, phase assemblages after sintering, and thermal stability of the phases are presented in Cai and colleagues 20–22,39 . The densities of the hot‐pressed samples were measured by the Archimedes method in water.…”

“…Details of the sintering process, phase assemblages after sintering, and thermal stability of the phases are presented in Cai and colleagues. [20][21][22]39 The densities of the hotpressed samples were measured by the Archimedes method in water. Microstructural observations of polished and fractured surfaces were carried out by scanning electron microscopy (SEM, JEOL JSM 880, Tokyo, Japan) and transmission electron microscopy (TEM, JEOL JEM 4010).…”

“…In another work, Hakeem et al 18 have indicated that hardness and glass transition temperature increase with nitrogen content; and processing of self‐reinforced microstructure consisting of elongated grains. In this way, Ca–α‐SiAlONs have shown 20–22 the advantages of a high solubility of Ca, a lower sintering temperature, and the increased possibility for formation of elongated grains yielding tougher and more creep‐resistant materials.…”