Development of efficient fabrication processes for highly functional silicon nitride ceramics: a review

Abstract

This study reviews the development of fabrication processes for silicon nitride ceramics with excellent mechanical properties, such as high fracture strength and fracture toughness. Silicon nitride ceramics with high wear resistance and thermal conductivity have been produced by tuning their composition and utilizing highly efficient processing techniques. The nitridation behavior of silicon powder in the presence of Zr compounds has been studied in order to assess the nitridation enhancement effect of zirconium during formation of reaction bonded silicon nitride. Thermogravimetric analysis has revealed that the addition of ZrO 2 to Si powder reduces the temperature of the main nitridation reaction. It is possible to produce reaction-bonded silicon nitride using a rapid nitridation technique with a heating rate of over 5°C/min, which is 80 times higher than that for the conventional reaction bonding process. A nitridation enhancement effect has also been observed with the addition of some rare-earth oxides. The reaction bonding process has been used to fabricate high-thermalconductivity silicon nitride ceramics with a relatively short processing time. Si 3 N 4 /carbon fiber composites have been developed using randomly dispersed high-tensile-modulus carbon fibers. The aligned silicon nitride grains and short carbon fibers in the composites result in both high fracture strength and toughness and a low friction coefficient under dry and water sliding conditions. The mechanical properties of the composites are anisotropic with respect to the grain alignment, with both strength and toughness being highest parallel to the extrusion direction. In this direction, the seeded specimen, with both silicon nitride grains and carbon fibers aligned, has higher fracture toughness and higher fracture strength than those of the non-seeded specimen, with only fibers aligned.

Effects of nitrogen pressure on properties of sintered reaction‐bonded silicon nitride

“…Silicon peaks are observed in none of the samples, indicating that the silicon was completely nitrided to Si 3 N 4 regardless of the N 2 pressure. Although the nitridation ratio does not reach 100% under any of the pressure, its low value indicates the effects of the vaporization of MgO and Si during the nitridation procedure 20 . The main phases can be identified as β–Si 3 N 4 and α–Si 3 N 4 , and the minor one is Y 2 Si 3 O 3 N 4 , a reaction product between Y 2 O 3 and Si 3 N 4 , and SiO 2 existing naturally on the surface of the reactant Si powder.…”

“…Although the nitridation ratio does not reach 100% under any of the pressure, its low value indicates the effects of the vaporization of MgO and Si during the nitridation procedure. 20 The main phases can be identified as β-Si 3 N 4 and α-Si 3 N 4 , and the minor one is Y 2 Si 3 O 3 N 4 , a reaction product between Y 2 O 3 and Si 3 N 4 , and SiO 2 existing naturally on the surface of the reactant Si powder. Figure 2B shows the ratio of β-Si 3 N 4 , which was calculated from the result in Figure 2A.…”

“…reported that cobalt removed the surface oxide film by forming Si‐Co eutectic liquid. Hyuga et al 19,20 . also revealed that adding zirconia promoted nitridation via the formation of ZrN, which reacted with SiO 2 .…”

“…Huang et al 18 reported that cobalt removed the surface oxide film by forming Si-Co eutectic liquid. Hyuga et al 19,20 also revealed that adding zirconia promoted nitridation via the formation of ZrN, which reacted with SiO 2 . Further, the oxide film can be removed by eutectic liquid formed by a reaction among Si 3 N 4 , SiO 2 , and sintering additives such as Y 2 O 3 , Yb 2 O 3 , La 2 O 3 , and Er 2 O 3 .…”

Experimental study on the effect of load and rotation speed on dry sliding of silicon nitride

“…Due to the special movement mode of spherical plain bearings, spherical plain bearing wear is mainly caused by sliding friction and the wear mechanism is mainly abrasive wear and adhesive wear (Love, 1957; Ghazali et al , 2013; Yunfan et al , 2021). With the large need and highly performance requirements of bearings, engineering ceramics represented by silicon nitride (Si 3 N 4 ) are widely used in bearing manufacturing due to their excellent physical and chemical properties including high strength, high hardness, high temperature resistance, corrosion resistance, wear resistance (Hampshire, 2007; 2009; Hyuga, 2018; Wang et al , 2000). Therefore, study on failure mechanism of Si 3 N 4 full-ceramic spherical plain bearings become an important part of bearing manufacturing.…”