Thermo-Mechanical Analysis of Si<sub>3</sub>N<sub>4</sub>-Based Seal Coatings on Si<sub>3</sub>N<sub>4</sub> Substrate

Abstract

In this Study, a Good Combination between Si3N4-Based Seal Coatings and Porous Si3N4Substrate Was Achieved by Room Temperature Spraying and Pressureless Sintering. To Evaluate the Joint Quality, Residual Stress due to Thermal Expansion Mismatch between the Coatings and Porous Layers Were Characterized by Computational Studies Using the Finite Element ANSYS Code. It Was Found that Si3N4-Based Seal Coating Allows a Gradual Change in Thermal Expansion Mismatch, Minimizing the Thermal Stresses Arising from Cooling or Heating. Further Theoretical Analysis Indicates that the Thermal Expansion Mismatch between the Two Layers Produced a Large Strengthening Effect for the Fraction of the Porosity below a Critical Level and that Substrates with the High Fraction of Porosity Showed Complete Cracking, as the Cracks Initiating in Adjacent Coatings. And the Volume Fraction of Pores Required to Cause Crack Deflection, in the Porous Layer, Was Predicted. The Effects of Layer Thickness and Porosity Fraction on Residual Stress Were Studied, which Are Used as Predictions towards Better Design of Composite Materials.