Tensile Creep of a Commercial-Grade Silicon Nitride, AS800: Limitation of Norton's Relationship

Published

February 19, 2017

Author(s)

H A. Maupas, B Hockey, Sheldon M. Wiederhorn

Abstract

Creep experiments were conducted on a commercial grade of silicon nitride (AS800) over a wide range of temperatures and stresses: 1200oC to 1370oC; 50 MPa to 400 MPa. Cavitation always accompanied creep. As with other grades of silicon nitride, the rate of cavity formation was found to be a linear function of the rate of creep deformation. Exponential or hyperbolic sine functions of applied stress fit the creep data much better than the simple power law function usually used to fit creep data. A comparison of the creep data with current theories of creep deformation suggests that the creep mechanism is one in which the rate limiting step for creep depends on either grain boundary sliding or cavity formation. We also discuss the creep rupture behavior of this material in terms of a Monkman-Grant plot, a plot of the logarithm of the strain rate versus the logarithm of the failure time. At temperatures of 1275oC and higher, experimental data follow a single curve. At 1200oC and 1250oC, data follow separate curves, the lower the temperature, the shorter the time to failure. The reasons for this change in creep rupture behavior below 1275oC are not understood.

Citation

Journal of the American Ceramic Society

Pub Type

Journals

Keywords

cavitation, ceramics, creep, high temperature, lifetime, silicon nitride

Citation

Maupas, H. , Hockey, B. and Wiederhorn, S. (2017), Tensile Creep of a Commercial-Grade Silicon Nitride, AS800: Limitation of Norton's Relationship, Journal of the American Ceramic Society (Accessed April 25, 2024)