High-Temperature Deformation and Fracture Behavior of Al_2O_3-Y_2O_3 Doped Silicon Nitride
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In order to clarify the high-temperature deformation and fracture behavior of Al<SUB>2</SUB>O<SUB>3</SUB>–Y<SUB>2</SUB>O<SUB>3</SUB> doped Si<SUB>3</SUB>N<SUB>4</SUB>, four-point bending tests were conducted at temperatures from room temperature to 1790 K and at strain rates from 1.5×10<SUP>−6</SUP>s<SUP>−1</SUP> to 3×10<SUP>−2</SUP>s<SUP>−1</SUP> in a nitrigen gas of 1.013×10<SUP>5</SUP>Pa (1 atm). As a result, the mechanical equation of state at yield stress was obtained as ε=A(σy⁄E)<SUP>m</SUP>exp(−Q/RT), where m=3.9 in the low temperature range or high strain-rate range, where m=1.7 in the high temperature range or low strain-rate range. The critical strain rate at which m changed shifted to high strain-rate side as temperature rises. It was suggested that plastic deformation of the Si<SUB>3</SUB>N<SUB>4</SUB> was controlled by grain boundary sliding with cavity formation in the range of m=1.7, and dislocation motion and micro-crack propagation in the range of m=3.9. The activation energy for deformation Q was almost independent of strain rate when m=3.9, while Q tended to increase with decreasing strain rate when m=1.7. The relationship between deformation and fracture in Si<SUB>3</SUB>N<SUB>4</SUB> was discussed on the basis of m value and fracture mode.
- MATERIALS TRANSACTIONS
MATERIALS TRANSACTIONS 37(3), 430-434, 1996-03
The Japan Institute of Metals