Slip Systems in FCC & BCC Crystals

SLIP SYSTEMS

The combination of a slip plane and slip direction is known as slip system. as slip system. Slip direction is the most important factor in slip system.

(i) Slip systems in F.C.C. crystals

In F.C.C. metals, plane (111) is the plane of maximum atomic density. There are four possible {111} slip planes namely, (1 1 1), (1 1 1)

Each plane contains three <110>, slip directions as shown in fig. 1.51 (a) for (1 1 1) plane. Fig. 1.51 (b) shows three slip systems with reference to (111) plane, i.e. (1 1 1) [1 1 0], (1 1 1) in f.c.c. crystals.

Thus there are 12 slip systems in f.c.c. metals. As there are so many (12) slip systems and that is why fcc metals are easily deformed, because there is always some plane and direction which is which is favourably oriented to permit plastic deformation.

(ii) Slip Systems in B.C.C Crystals

In BCC metals, slip occurs predominately on { 1 1 0 } < 1 1 1> slip system. {110} planes have highest atomic density. There are six plane in {110} family and each plane has two directions. Thus there are 12 such slip systems.

Fig. 1.51 shows one such plane (0 1 1) and two directions The two slip system based on (011) plane are: (011) There are 12 + 24 = 36 ((0 1 1), (1 1 2) and (3 2 1) slip planes) more slip system in B.C.C metal which are less predominant.