Characterization of Si3N4-Al interface after corrosion tests

Abstract

Silicon nitride is a covalent ceramic material of high corrosion resistance and mechanical stability at elevated temperatures. Due to these properties, its use in metallurgical processes, such as the casting of alloys, is increasing. Therefore, the characterization of the interface between Si3N4 and the casted metal is of great importance to investigate possible interactions, which might deteriorate the ceramic mould or contaminate the metal. In this work, the use of Si3N4 as crucible material for Al-casting has been studied, by investigating the corrosion attack of liquid Al at a temperature of 1150 ºC during 30 days in air. The interface was characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. It has been found that due to superficial oxidation two oxide layers form - SiO2 on Si3N4 and Al2O3 on Al - which effectively hinder further reactions under the conditions studied, confering high corrosion resistance to the Si3N4 crucible.

Dense and near-net-shape fabrication of Si3N4 ceramics

“…at high temperatures (1750-2000 • C) [3][4][5][6][7][8][9] depended on the surface oxygen content of the powders [6]. However, the sintering of silicon nitride ceramics without additives is an important approach to reducing impurity phases in the densified bodies achieving Si 3 N 4 ceramics with the intrinsic properties of the materials.…”

“…Taking into account their unique combination of properties, silicon nitride and related materials have probably become the most thoroughly characterized non-oxide ceramics with wide applications including heat exchangers, turbine and automotive engine components, valves and cam roller followers for gasoline and diesel engines and radomes on missiles as well as insulators, electronic substrates, high Tc superconductors, tool bits, wear surfaces, to name a few [2,[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The market for these applications is very high; there are still several difficulties that must be overcome before the full potential of structural ceramics based silicon nitride is realized.…”

“…The sintering of silicon nitride is very difficult because of the low self-diffusivity of this covalent material [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Doping pure Si 3 N 4 with of some oxides provides the formation of intergranular liquid phase which aids the further densification of the silicon nitride during different sintering routes [3][4][5][6][7][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. These oxides, however, remain as grain boundary glassy phase, which deteriorate the high temperature properties of the ceramics such as creep and high temperature strength [17,32,33].…”