Elevated Temperature Deformation of Single Crystal Y 3Al 5O 12

Abstract

Single crystal oxides with complex crystal structures having large unit cells and consequently, large Burgers vectors have recently received attention as possible fiber-reinforcements in oxide/oxide composites for use at temperatures greater than 1,500 C. One such single crystal oxide is Y{sub 3}Al{sub 5}O{sub 12} (Yttrium Aluminum Garnet or YAG). At present both dislocation glide and climb have been suggested as the rate-controlling deformation mechanism for single crystal Y{sub 3}Al{sub 5}O{sub 12} above 1,600 C at stresses below 300 MPa. The choice of the specific creep mechanism was based on the nature of the creep transient, value of the stress exponent, activation energy for creep and examination of the deformed microstructure obtained from constant strain-rate tests. The present investigation was undertaken to: (1) determine whether the creep behavior of single crystal Y{sub 3}Al{sub 5}O{sub 12} is controlled by, dislocation glide or climb by examining the nature of the creep transient upon initial loading and after a stress change using constant stress tests and (2) verify that the existing steady-state creep data for single crystal Y{sub 3}Al{sub 5}O{sub 12} obtained from constant strain-rate tests are in agreement with the constant stress tests.