On the mechanism of anomalous slip in bcc metals

The anomalous-slip behavior of bcc metals has been studied by TEM analyses of dislocation substructures developed in a [ 2 ¯   9   20 ] -oriented Mo single crystal uniaxially compressed at room temperature to a total-strain of 0.4%. It is found that the initial dislocation lines in association with “grown-in” super-jogs can act as effective sources for the formation of both a0/2[1 1 1] (Schmid factor = 0.5) and a 0 / 2 [ 1   1 ¯   1 ] (Schmid factor = 0.167) coplanar screw dislocation arrays in the ( 1 ¯   0   1 ) primary slip plane. The interaction between the multiplied a0/2[1 1 1] dislocations and pre-existing a 0 / 2 [ 1   1 ¯   1 ] dislocation segments, which block the motion of the a0/2[1 1 1] dislocations, renders the multiplication of a 0 / 2 [ 1   1 ¯   1 ] dislocations and leads to the formation of a0/2[1 1 1] and a 0 / 2 [ 1   1 ¯   1 ] dislocation arrays on the ( 1 ¯   0   1 ) primary slip plane. The occurrence of { 0   1 ¯   1 } anomalous slip is accordingly proposed to be resulting from the mutual trapping of a0/2[1 1 1] and a 0 / 2 [ 1   1 ¯   1 ] coplanar dislocation arrays on the ( 1 ¯   0   1 ) primary slip plane, which renders a cross-slip propagation of both a0/2[1 1 1] and a 0 / 2 [ 1   1 ¯   1 ] screw dislocations from the ( 1 ¯   0   1 ) plane onto the { 0   1 ¯   1 } planes and thus activates the { 0   1 ¯   1 } 〈1 1 1〉 slip systems.