Plastic flow of Ni3(Si,Ti) Single crystals

The flow stress of L1₂-type Ni₃(Si, Ti) by the compression test was measured as a function of temperature, strain rate, orientation and alloy composition. The critical resolved shear stress (CRSS) increased from 77 K, reached a peak, and then decreased rapidly with increasing temperature. The single crystals with orientations close to [011] and [1̄11] showed the operations of octahedral slips (111) [1̄01] below the peak temperature and of cube slips (001) [1̄10] above the peak temperature, whereas those with orientation close to [001] showed the operations of octahedral slips {111} over the entire temperatures. The CRSS depended on the orientation and alloy composition below the peak temperature but on the orientation and the strain rate above the peak temperature. The peak temperature was dependent on the orientation but almost independent of the strain rate and alloy composition. It is suggested that the deformation mechanisms for Ni₃(Si, Ti) single crystals are quite similar to those for other Ni-based L1₂ single crystals such as Ni₃Al, Ni₃Ga and Ni₃Ge; at low temperatures the dislocation movement of the superpartials dissociated on (111) plane with APB became sessile by micro cross slip to (001) plane. At high temperatures, two deformation modes were operative, depending on the orientation. The deformation of the single crystals with orientations far from [001] is due to the Peierls-Nabarro mechanism of (001) [1̄10] slip, whereas the deformation of the single crystals with orientations close to [001] is due to the intrusion of the “diffusive” process of (111) [1̄01] slip.