  The plastic deformation of Cr3+ -doped a-Al2 O3 (ruby) with four distinct Cr
concentrations has been studied at temperatures between 900 and 1500 $^\circ$C.
The mechanical tests indicate that the processes of dislocation multiplication
and the adjustments of the slip velocity of these dislocations to the imposed
strain rate in undoped a-Al2 O3 are not significantly affected by the Cr
concentra%on. The yield stress increment is approximately constant with
temperature and the hardening increases with the Cr concentration. The critical
resolved shear stress (CRSS) is fixed to a model based on dislocation glide
controlled by the nucleation and propagation of kink pairs, modified to include
the hardening due to Cr. Satisfactory fits are achieved with adjustable
parameters close to those employed for undoped a-Al2 O3 .
