Microstructural design of silicon nitride with improved fracture toughness: I, Effects of grain shape and size
Journal
Journal of the American Ceramic Society
Journal Volume
81
Journal Issue
11
Pages
2821-2830
Date Issued
1998
Author(s)
Becher P.F.
Sun E.Y.
Plucknett K.P.
Alexander K.B.
Hsueh C.-H.
Lin H.-T.
Waters S.B.
Westmoreland C.G.
Kang E.-S.
Hirao K.
Brito M.E.
Abstract
The use of self-reinforcement by larger elongated grains in silicon nitride ceramics requires judicious control of the microstructure to achieve high steady-state toughness and high fracture strength. With a distinct bimodal distribution of grain diameters, such as that achieved by the addition of 2% rodlike seeds, the fracture resistance rapidly rises with crack extension to steady-state values of up to 10 MPa¡Pm 1/2 and is accompanied by fracture strengths in excess of 1 GPa When the generation of elongated reinforcing grains is not regulated, a broad grain diameter distribution is typically generated. While some toughening is achieved, both the plateau (steady-state) toughness and the R-curve response suffer, and the fracture strength undergoes a substantial reduction. Unreinforced equiaxed silicon nitride exhibits the least R-curve response with a steady-state toughness of only 3.5 MPa¡Pm 1/2 coupled with a reduced fracture strength.
Type
journal article