Plastic deformation kinetics of fine-grained alumina

Abstract

The plastic deformation kinetics of a commercial fine-grained alumina with ϳ300 ppm MgO and grain sizes from 1.4 to 2.9 m were determined in tension at 1475 ЊC to 1600 ЊC and strain rates from 10 Ϫ5 to 10 Ϫ3 s Ϫ1 , employing stress relaxation (SR) as the principal test mode. The constants in the Weertman-Dorn (W-D) equation were determined and had the following values: A ϭ 2.9 Ϯ 0.5 ϫ 10 9 , n ϭ 2.2 Ϯ 0.1, p ϭ 1.9 Ϯ 0.1, Q ϭ 492 Ϯ 3 kJ/mole, and threshold stress 0 ϭ 0. These constants are in accord with grain boundary sliding (GBS) accommodated by dislocation glide and climb with Al 3ϩ ion lattice diffusion as the rate-controlling mechanism.

Influence of an electric field on the plastic deformation of fine-grained Al2O3

“…Such a plot is given in Figure 10 the idea that lattice diffusion of the Al 3ϩ ions is the rateconstants for grain-boundary diffusion are not known for the specific composition of the present material, and because controlling accommodation process for grain-boundary sliding. [15] However, the value of Q ϭ 880 to 1070 kJ/mole for data are not available for the influence of an electric field on lattice diffusion in alumina, a quantitative assessment of plastic deformation with E ϭ 300 kV/cm is more in accord with that for either Al 3ϩ or O 2Ϫ sub-boundary or grainthe change produced by the field in the grain-boundary sliding accommodation mechanism from lattice to grain-boundboundary diffusion, with better agreement occurring for the oxygen ions. Further, if we assume that because the field ary diffusion is not possible at this time.…”

“…In this approach, a plot of [Ѩ ln /Ѩ] Ϫ1 vs should yield a straight controlling mechanism, and kT and RT have their usual meaning. The prior work without a field [15] gave A* ϭ 6.5 ϫ line of slope 1/n* and intercept O . Such a plot is given in Figure 8 for the SR tests with E ϭ 300 V/cm and furnace 10 4 m 2 /s, n ϭ 2.2, p ϭ 1.9, and Q ϭ 492 kJ/mole, which are in accord with grain boundary sliding accommodated by temperatures of 1450 ЊC and 1475 ЊC.…”

“…The applied voltage article. [15] Here, we will compare the results obtained with the field with those given there. was maintained constant at 1.5 kV, which gave a current flow I ϭ 10 to 20 mA.…”

“…[18] 300 V/cm. The stress exponent n E was determined from C. Plastic Deformation Kinetics Parameters strain-rate-cycling (jump) tests and from stress-relaxation It was determined in the tests without an electric field [15] (SR) tests. The results for the SR tests are presented in that the plastic deformation kinetics of the present, fine- Figure 7; they give n E ϭ 2.2 when the data are corrected for grained Al 2 O 3 were in accord with the Weertman-Dorn the electric field-induced swelling.…”

“…[6] In powder doped with ϳ300 ppm MgO used in the studies in the contrast to the reduction in flow stress during SPD of the companion article. [15] Dog-bone shaped tensile specimens Al alloys, an electric field reduced the creep rate (i.e., (Figure 1) with gage dimensions of 14 ϫ 3.4 ϫ 2 mm were increased the flow stress) during SPD of the Zn-5 wt pct fabricated from the spray-dried powder by dry pressing (207 Al alloy. [7] In the case of ceramics, an electric field of ϳ1…”