Influence of nano–micrometre powder blends on microstructure and mechanical properties of silicon nitride

Abstract

A well known route to making tough silicon nitride compositions is to control the grain size and aspect ratio distributions. This is usually done by choosing the appropriate powder characteristics, sintering conditions, as well as sintering additives. The effect of hot pressing a blend of nano and micrometre scale silicon nitride powder is explored here. Microstructures and mechanical properties are determined for these hot pressed ceramics and are compared with a reference silicon nitride. Hardness and fracture toughness are determined at room temperature using hardness indents produced by a macro Vickers hardness indenter. Grain size and aspect ratio distributions and their impact on mechanical properties are presented. Blending of nano and micrometre scale powder is shown to result in a refined microstructure with an increase in the area/volume fraction of finer grains. Rising R curves are established for these ceramics demonstrating toughening behaviour. Crack bridging and crack path deviation are identified as possible toughening mechanisms.

Low temperature sintering of Si3N4ceramics by spark plasma sintering technique

“…2 s f~3 PL 2bd 2 (1) where P is the load at a given point on the load deflection curve (N), L is the support span (mm), b is the width of the test beam (mm) and d is the depth of the tested beam (mm).…”

“…[1][2][3] There are two crystallographic forms of Si 3 N 4 : a-Si 3 N 4 and b-Si 3 N 4 . The a-Si 3 N 4 is unstable at high temperature and is reported to transform to b-Si 3 N 4 over 1400uC under the existence of a liquid phase.…”

“…Si 3 N 4 ceramic has superior physical, chemical and high temperature mechanical properties and has become one of the most studied advanced ceramic as an important candidate for a variety of technical and engineering applications. [1][2][3] There are two crystallographic forms of Si 3 N 4 : a-Si 3 N 4 and b-Si 3 N 4 . The a-Si 3 N 4 is unstable at high temperature and is reported to transform to b-Si 3 N 4 over 1400uC under the existence of a liquid phase.…”

“…Si 3 N 4 ceramic has superior physical, chemical and high temperature mechanical properties and has become one of the most studied advanced ceramic as an important candidate for a variety of technical and engineering applications 1 – 3. There are two crystallographic forms of Si 3 N 4 : α ‐Si 3 N 4 and β ‐Si 3 N 4 .…”

Preparation of β-Phase Silicon Nitride Powders

“…For β-Si 3 N 4 , the final grain size and shape distributions are dictated by the starting silicon nitride powder characteristics [7], the sintering additives and the processing conditions [8]. So, the appropriate sintering additives and excellent sintering conditions shoud be chosen to facilitate the alpha to beta phase transformation [9]. In this paper, β-Si 3 N 4 were prepared in large quantity by mixing the precursor of silicon under high-purity nitrogen gas atmosphere with α-Si 3 N 4 as diluent and FeCl 3 as catalyst at 1400℃ for 2 hours in the pure nitrogen gas in this paper.…”