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High‐Temperature Creep and Cavitation of Polycrystalline Aluminum Nitride
Author(s) -
Jou Zuel Chown,
Virkar Anil V.
Publication year - 1990
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1990.tb05247.x
Subject(s) - creep , materials science , crystallite , cavitation , activation energy , composite material , grain size , dislocation , hot pressing , nitride , grain boundary , metallurgy , thermodynamics , microstructure , chemistry , physics , organic chemistry , layer (electronics)
Dense, polycrystalline AlN samples of grain size between 1.8 and 19 μm were fabricated by hot‐pressing. Bar‐shaped samples were subjected to creep in four‐point bending under static loads in nitrogen atmosphere. The outer fiber stress was varied between 20 and 140 MPa and the temperature between 1650 and 1940 K. Steady‐state creep rate, dɛ/d t was proportional to σ n d − m where the stress exponent, n , was between 1.27 and 1.43 and grain‐size exponent, m , between ∼ 2.2 and ∼ 2.4. The activation energy for creep ranged between 529 and 625 kJ/mol. Both round (r type) and wedgeshaped (w type) cavities were observed in electron micrographs of the deformed samples. No noticeable change in the dislocation density was observed. Contribution of cavitation to the creep rate was estimated using an unconstrained cavity model. Based on this study it is concluded that the dominant mechanism of creep in polycrystalline AlN is diffusional.