Plastic flow of Co 3 Ti single crystals

Abstract

The flow stress of Co 3Ti single crystals (Ll 2 structure) by compression test was measured as a function of temperature, orientation, chemical composition and strain rate. The critical resolved shear stress (CRSS) showed a rapid increase with decreasing temperature below about 500 K, a remarkable increase with increasing temperature above about 500 K, and then a sharp decrease above the maximum temperature (about 900–1100 K). It was found that in all samples octahedral {111} slip occurs over the entire range of test temperatures. An exceptional slip, i.e. a cube {100} slip was found in sample having orientation axis near [1̄11] and tested above the maximum temperature. The CRSS depended on neither orientation nor strain rate below the minimum temperature but depended on both orientation and strain rate above the minimum temperature. The maximum temperature was dependent of orientation, chemical composition but almost independent of strain rate. It was suggested that the plastic flow of Co 3Ti single crystals below the minimum temperature is responsible for the dislocation movement of the superpartials dissociated on the (111) plane with the SISF. The plastic flow between the minimum and maximum temperatures is due to thermally activated cross-slip from (111) to (001) plane. It was also suggested that the decrease of the CRSS above the maximum temperature is probably due to the intrusion of diffusive process, i.e. unlocking process on cross-slipped (111) dislocation motion.