On the mechanism of anomalous slip in bcc metals

▶ Understanding the anomalous slip behavior of bcc metals. ▶ TEM observation of coplanar screw-dislocation arrays. ▶ TEM analysis for the formation of 〈0 1 0〉-type junction dislocations. ▶ A novel mechanism proposed for the 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 a 0/2[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 a 0/2[1 1 1] dislocations and pre-existing a 0 / 2 [ 1 1 ¯ 1 ] dislocation segments, which block the motion of the a 0/2[1 1 1] dislocations, renders the multiplication of a 0 / 2 [ 1 1 ¯ 1 ] dislocations and leads to the formation of a 0/2[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 a 0/2[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 a 0/2[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.