Fracture strengths and microstructures of Si3N4/SiC nanocomposites fabricated by in-situ process

doi:10.1016/S1359-6462(01)00886-7

Scripta Materialia

Volume 44, Issues 8–9, 18 May 2001, Pages 2079-2081

https://doi.org/10.1016/S1359-6462(01)00886-7 Get rights and content

Abstract

Si₃N₄/SiC nanocomposites was prepared by in-situ process using commercial phenolic resin. Microstructures were examined by Transmission Electron Microscopy and Scanning Electron Microscopy. The room and high temperature fracture strengths of Si₃N₄/SiC nanocomposites have been studied using the 3-point bending test. The fracture strength of Si₃N₄/SiC nanocomposites with Al₂O₃ and Y₂O₃ doped samples was about 1100 MPa at room temperature. The fracture strength of Si₃N₄/SiC nanocomposites with only Y₂O₃ doped samples was about 1100 MPa at room temperature and 800 MPa at 1400°C. The grain boundary phases formed during sintering process were examined by X-ray Diffraction method.

Introduction

Various processes have been followed to produce Si₃N₄/SiC nanocomposites. It was reported that the Si-C-N powder production as a precursor of nanocomposites via the pyrolysis of a polymethylsilazane precursor, (1) laser irradiation of gas mixtures, (2) and laser interaction with droplets of a liquid hexamethyldisilazane precursor.(3) Also, powder mixing method was used for fabrication of Si₃N₄/SiC nanocomposites. 4, 5 More recently, we developed a new route to in-situ fabricate Si₃N₄/SiC nanocomposites, assuming that Si₃N₄ and/or silicon oxide reacts with free carbon formed by decomposition of a polymer during heat treatments.(6) This reaction yielded a homogeneously dispersed Si₃N₄/SiC nanocomposite, thereby eliminating the use of SiC powder with more efficient processing.

In this study, the 3-point bending test was used for measuring fracture strength of the fabricated Si₃N₄/SiC nanocomposite and the phases of samples were analyzed by X-ray diffraction (XRD) method. The microstructure of Si₃N₄/SiC nanocomposite were analyzed by transmission electron microscopy (TEM). From the results of these investigations, we tried to explain the relationship between microstructure/grain boundary phases and fracture strength of the in situ processed Si₃N₄/SiC nanocomposite.

Section snippets

Experimental procedure

Si₃N₄/SiC nanocomposite was prepared by in situ process using α-Si₃N₄ powder and commercial polymers. In situ process means that a polymer will be converted to the carbon and it transformed to SiC particles by several heat treatments. The used α-Si₃N₄ powder (SN-E10, Ube Industries, Tokyo, Japan) had a mean particle size of 200 nm and contained oxygen (<1.26 vol.%) as a main impurity.

The phenolic resin ([-CH₂(C₆H₅)OH-]_n, Phenolite 739, Kangnam Chemicals, Incheon, Korea; 3511g/mol) was used for

Results and discussion

Fig. 1 shows that the results of fracture strength of SNP4-4Y and SNP4-8Y at room temperature and 1400°C. They show the average value of 1100MPa at room temperature and 800MPa at 1400 °C. The reason of retain of high temperature strength at 1400°C might be the hinder of grain boundary sliding by SiC nanoparticles.

From the observation of microstructure of SNP4-8Y (Fig. 2), the SiC nanoparticles are well distributed in grain or grain boundaries. The agglomerates (CNx phases) are not observed.

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Fracture strengths and microstructures of Si3N4/SiC nanocomposites fabricated by in-situ process

Abstract

Introduction

Section snippets

Experimental procedure

Results and discussion

J. Eur. Ceram. Soc.

Composites Part A

J. Alloys Compd.

J. Am. Ceram. Soc.

Fracture strengths and microstructures of Si₃N₄/SiC nanocomposites fabricated by in-situ process