Production of Si3N4-Based Articles and their Application in Aerospace Industry

Abstract

As required by the purpose and operating conditions of the articles, Si3N4-based ceramic materials must have a combination of properties ensuring their serviceability, while their manufacturing process must afford the manufacture of complex-shaped products. The paper deals with the technology of making complex-shaped articles from reaction-bonded, densified silicon nitride in the system Si3N4, Si3N4-BN, Si3N4-Al2TiO5, Si3N4–Si by thermoplastic slip casting of a fine high-purity silicon powder comprising additives or sintering aids with subsequent nitridation at temperatures up to 1500°C or additional sintering up to 1750-1800°C. In the process of making reaction-bonded silicon nitride, consideration is given to the exothermal effect of reaction, to the influence of additives on the properties of ceramics and the manufacturing process. Methods of oxidation protection of porous Si3N4-based ceramics and adaptation of these methods to protection of porous SiC- or SiC-C – based ceramics are discussed. Upon densification of reaction-bonded silicon nitride at temperatures up to 1750- 1800°C, consideration is also given to the effects of diffusion processes of the additives, used as sintering aids, on ceramics microstructure. The mechanisms of dissolution – recrystallization of α- and β-Si3N4 in the course of forming the self-reinforced ceramic structure are discussed. The peculiarities of making Si3N4-Si – based material having unusual properties including the mechanism of forming, oxidation resistance, electrical conductivity and high impact resistance are covered. The paper presents the results of testing of the ceramic components and units of gasturbine engines, bearings and attachments of the spacecraft Buran, and it also gives test data with reference to the ceramic parts tested at temperatures above 2000°C.