# Experimental Study on ELID Grinding of Silicon Nitride Ceramics for G5 Class Bearing Balls
## 1 Introduction  
Silicon nitride (Si\({}_{3}\)N\({}_{4}\)) is a prominent non-oxide ceramic material known for its advantageous properties. It has a low density, making it lightweight, and its coefficient of thermal expansion is similar to that of silicon. Silicon nitride exhibits high strength, hardness, and fracture toughness, along with excellent resistance to wear, oxidation, thermal shock, and thermal fatigue. These outstanding mechanical, thermal, and chemical characteristics make it a versatile material suitable for structural components and electronics applications. Silicon nitride is a functional material with exceptional mechanical, physical, and chemical properties, and it holds significant potential for a wide range of applications, including extreme environmental conditions, making it a material with immense future prospects. As a structural material, silicon nitride boosts outstanding properties such as high strength, hardness, chemical stability, high-temperature strength, wear resistance, thermal conductivity, and a low coefficient of thermal expansion. It finds extensive applications in various fields, including power electronics components for electric vehicles, heat sinks, automotive bearings, semiconductors, and aerospace components [1]. Silicon nitride has been developed as hypersonic guided munition material, leveraging its excellent dielectric properties, mechanical strength, thermal shock resistance, and particle erosion resistance [2]. As anelectrical and electronic material, silicon nitride (Si\({}_{3}\)N\({}_{4}\)) is expected to find applications in the semiconductor industry, particularly in the production of next-generation memories such as DRAM (dynamic random access memory) and flash memory. It is anticipated to be used in a thin-film format, serving as an insulating layer, passivation treatment, diffusion prevention mask, and more [3]. Research has also been conducted to improve the adhesion of the electrode layer when forming it through a wet process on silicon nitride ceramic substrates, which exhibit excellent electrical properties and high thermal conductivity [4]. Silicon nitride is also known to be a suitable ceramic material for bearing applications due to its favorable mechanical and physical properties, as well as its reliability in terms of rolling fatigue life [5; 6; 7; 8; 9; 10]. It exhibits excellent material characteristics such as high density, strength, and heat resistance. When used as a rolling element in bearings, silicon nitride reduces centrifugal load owing to its low density and enhances bearing rigidity due to its low elastic modulus [10]. Moreover, its outstanding friction characteristics lead to low heat generation and a low coefficient of thermal expansion. However, it is essential to note that silicon nitride is a challenging material to sinter due to thermal decomposition at high temperatures and its low diffusion coefficient with a 70% strong covalent bonding ratio. The densification of silicon nitride ceramics occurs through the reaction of silica on the surface of silicon nitride particles, resulting in the formation of a low-melting liquid phase. During the densification process, the liquid phase generated at the grain boundaries remains in an amorphous glassy phase after cooling. This phenomenon significantly influences the growth, fracture toughness, and high-temperature properties of silicon nitride crystals, leading to a deterioration of silicon nitride's properties. The rolling fatigue life of silicon nitride is improved when it possesses a uniform and small particle microstructure with no pores and secondary phases, as well as fewer grain boundary phases [11; 12; 13]. Recent research has been focused on low-temperature densification sintering to achieve a uniform fine particle structure, aiming to enhance mechanical properties such as wear resistance, strength, and hardness, which are crucial for bearing rolling components.