HIGH-TEMPERATURE CREEP OF SINGLE-CRYSTAL GADOLINIUM GALLIUM GARNET

High temperature creep of single crystal gadolinium gallium garnet (GG G) was studied in the temperature range of 1723-1853 K (0.86-0.94 T-m, T-m: melting temperature) and strain rate from 9 . 10(-7) s(-1) to 2 . 10(-5) s(-1). The compression tests were made along the [100] and [1 11] orientations. We have performed both constant strain-rate and stre ss-dip tests. For the [100] orientation, deformation occurs via the [1 11] <{1(1)over bar 0}> slip systems. For the [111] orientation, both t he [100] {010} and the [111] <{1(1)over bar 0}> slip systems can be ac tivated. GGG garnet is very strong under these conditions: sigma/mu = (1-3) x 10(-3) (sigma: creep strength, mu: shear modulus). The creep b ehavior is characterized by a power law with stress exponent n = 2.9-3 .3 and high activation energies E = 612-743 kJ/mol (E* similar to 45 x RT(m), at zero stress which decrease with the increase of stress). S tress-dip tests suggest a small internal stress (sigma(i)/sigma simila r to 0.62; sigma(i): internal stress, sigma: applied stress) compared to other materials. These results suggest that the high creep strength of GGG is mainly due to difficulty of dislocation glide rather than d islocation climb.