Microstructure Simulation And Mechanical Properties Prediction For In-situ Toughened Silicon Nitride

With the development of computer and artificial intelligence techniques, materials design is becoming one of three main parts of materials science and technology with experiments and theories. Taking in-situ toughened silicon nitride as a design object, principle component analysis (PCA) is applied to study the microstructure and mechanical properties, to find out the main microstructure controlling factors, and to simplify the characterization variables and criterions; fuzzy neural networks (FNNs) is also applied to develop a design expert system for this material, which can realize the forward prediction from processing, microstructure to mechanical properties, and backward design from mechanical properties or microstructure to processing; Monte-Carlo method is applied to simulate the grain growth of this material, and then crack propagation is simulated, which is another way based on physics and chemistry to developing prediction models from processing until to mechanical properties. Uniform pattern of materials design is discussed finally. The main results are listed below:1. Microstructure of in-situ toughened Si3N4^ can be characterized with the first principle component of the original eight characterization variables, namely, a complex microstructure index. This index reflects the comprehensive microstructure characteristics and the contrasts between the micro structure's comprehensive status and its variance. Compact matrix (large value of ρ') with fine grains (small value of d1) and uniform large grains (small value of Y2 × 100 ) with great aspect ratio (large value of AR2) must be ensured in order to get in-situ toughened Si3N4 with excellent microstructure.2. Mechanical properties of in-situ toughened Si3N4 can be characterized with the first and the second principle components, namely, mechanical properties stability index and average mechanical properties index. The former index reflects fracture toughness and Weibull modulus which are affected by the fluctuation of microstructure; the later one reflects the average mechanical property, namely rupture strength.3. Simpler microstructure and mechanical properties classification criterions have been established. If F1≥ 3.8, the grains must be large grains; if 0 ≤F1<3.8, thegrains must be medium grains; if F1 < 0 , the grains must be fine grains. In-situ toughened Si3N4 with highest and stable mechanical properties can be obtained ifF1'>0.7 and -0.5