EFFECT OF TEST TEMPERATURE AND STRAIN-RATE ON THE YIELD STRESS OF MONOCRYSTALLINE 6H-SIC

The critical resolved shear stress for activating the (0001) (2<(11)ov er bar>0) slip system of monocrystalline 6H-SiC has been determined as a function of test temperature and strain rate via constant-displacem ent compression tests. Tests were conducted at temperatures between 55 0 and 1300 degrees C at strain rates of 1.3 x 10(-4), 6.3 x 10(-5) and 3.1 x 10(-5) s(-1). The current study shows that 6H-SiC crystals can be plastically deformed via relatively modest resolved shear stresses on the basal plane at temperatures as low as approximate to 550 degree s C. For temperatures below approximate to 1300 degrees C for the fast and intermediate strain rates, and for temperatures below approximate to 1100 degrees C for the slow strain rate, the stress exponent n, an d the activation enthalpy H were estimated to be (3.0 +/- 0.7) and (2. 1 +/- 0.7) eV, respectively. At higher temperatures at the slowest str ain rate: the activation enthalpy was determined to be (4.5 +/- 1.2) e V. Subsequent to the deformation tests, transmission electron microsco py (TEM) was used to rationalize some of the results.