Improved mechanical properties and dimensional accuracy of silica-based ceramic cores by Si3N4 addition

Silica-based ceramic cores are extensively used to form the complex hollow structure inside turbine blade. However, the excellent mechanical properties and high dimensional accuracy of ceramic cores are very crucial to obtain the hollow turbine blade with high precision, which is still a challenging work. In this study, silica-based ceramic cores with silicon nitride addition were prepared for improving the mechanical properties and dimensional accuracy. Results showed that the linear shrinkage of silica-based ceramic cores significantly decreased from 1.21% to 0.087% and the porosity gradually increased from 17.9% to 22.1% with the increase of Si3N4 content. The weight gain of cristobalite in the core samples after sintering first increased and then decreased, where the sample with 5wt.% Si3N4 had the maximum cristobalite content of 4.4wt.%. The appropriate Si3N4 content (5wt.%) in the silica-based ceramic cores could enhance the flexural strength at room temperature to 16.84MPa by promoting densification process. However, the excess Si3N4 content (more than 10wt.%) could hinder the densification process and enlarge their porosity, decreasing the flexural strength at room temperature. Meanwhile, the high temperature strength at 1500°C was decreased owing to the increasing porosity caused by the re-oxidation of Si3N4 particles. Therefore, it was concluded that the silica-based ceramic cores with 5wt.% Si3N4 showed higher mechanical properties and lower linear shrinkage, which offered a way to maintain the excellent mechanical properties and high dimensional accuracy of ceramic cores.