High‐Temperature Creep and Cavitation of Polycrystalline Aluminum Nitride

Abstract

Dense, polycrystalline AIN samples of grain size between 1.8 and 19 pm were fabricated by hot-pressing. Bar-shaped samples were subjected to creep in four-point bending under static loads in nitrogen atmospbere. The outer fiber stress was varied between 20 and 140 MPa and the temperature between 1650 and 1940 K. Steady-state creep was established in each of the tests. The steady-state creep rate, de/dt was proportional to d d -" 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 AIN is diffusional. [

High temperature plastic deformation of aluminium nitride with a lower-oxygen content

“…Our activation energy ∼8.25 eV is significantly larger than reported in earlier work, between 5.4 and 6.3 eV [7,8].…”

“…A comparison can be done with Jou and Virkar [7]. Interpolating their data for our grain size and extrapolating them, with their stress exponent, in our stress range, we obtain, at 1823 K, creep rates which are of the order of those measured by Feregotto [5,6] and much larger than present ones.…”

“…Interpolating their data for our grain size and extrapolating them, with their stress exponent, in our stress range, we obtain, at 1823 K, creep rates which are of the order of those measured by Feregotto [5,6] and much larger than present ones. Also, the large amount of cavitation observed in [7] makes clear that their AlN was not so pure and had weak grain boundaries.…”

“…Creep behaviour was studied in detail by two groups: Jou and Virkar [7] used four-point bending with maximum stress ranging from 20 to 140 MPa, at temperatures comprised between 1650 and 1940 K, with special attention paid to the grain size dependence of the creep rate, for average grain sizes between 1.8 and 19 m. Vasudev et al [8] used compression testing in the range 100-370 MPa, between 1470 and 1670 K, with very fine-grained (average grain size ∼0.7 m) AlN hot-pressed without additives. These two works do not report on dislocations.…”

Combustion synthesis of hexagonal AlN–SiC solid solution under low nitrogen pressure

“…Aluminum nitride (AlN) is a promising advanced ceramic because of its excellent physicochemical properties, such as high thermal conductivity, high electrical resistance, low dielectric constant, low thermal expansion coefficient, good thermal shock resistance, as well as good corrosion resistance [2][3][4][5]. Therefore, AlN is especially considered for many heat-dissipation applications such as IC packaging materials, heat sink, and high thermally conductive composites.…”