不規則γ析出相を含むγ′-Ni<SUB>3</SUB>(Al, Ti)L1<SUB>2</SUB>型規則相単結晶の強度の方位依存性

Abstract

An investigation of the mechanical behavior of γ′-L12 ordered Ni3(Al, Ti) single crystals containing fine dispersion of disordered γ particles was perfornned for several different crystal orientations over the temperature range of 77 to 1273 K. Slip systems were determined by two-surface trace analysis and dislocation structures were observed by the weak-beam method of transmission electron microscopy (TEM). The critical resolved shear stress (CRSS) for (111)[\bar101] slip increases with increasing temperature in the temperature range where (111) slip operates, but it decreases as (010) cube cross slip commences. The CRSS for (111)[\bar101] slip is dependent on crystal orientation in the corresponding temperature range. For the samples of [001] orientation, (111)[\bar101] slip operates over the whole temperature range of experiment, but for those of other orientations, the cross slip occurs from (111) to (010). The temperature where the strength reaches a maximum (peak temperature) is dependent on crystal orientation; the higher the ratio of the Schmid factors of (010)[\bar101] to that of (111)[\bar101] (N value), the higher the peak temperature. When compared with that of the γ′-Ni3(Al, Ti) single phase the orientation dependence of CRSS and peak temperature becomes small, and it was also shown that the larger the N value, the higher the strength at the same temperature. The peak temperatures were increased by the precipitation of γ particles for the samples of all orientations. Electron microscopy of deformation induced dislocation arrangements under peak temperature has revealed that most of dislocations are straight screw dislocations. The mobility of screw dislocations decreases with increasing temperature. Above the peak temperature, dislocations begin to cross slip from the (111)[\bar101] slip system to the (010)[\bar101] slip system, thus decreasing the strength. However, for the samples of [001] orientation, cross slip does not occur up to 1073 K.