Papers by Keyword: Lattice Invariant Shear

Abstract: Shape memory effect is a peculiar property exhibited by certain alloy systems, and shape memory alloys are recognized to be smart materials. These alloys have important ability to recover the original shape of material after deformation, and they are used as shape memory elements in devices due to this property. The shape memory effect is facilitated by a displacive transformation known as martensitic transformation. Shape memory effect refers to the shape recovery of materials resulting from martensite to austenite transformation when heated above reverse transformation temperature after deforming in the martensitic phase. These alloys also cycle between two certain shapes with changing temperature.Martensitic transformations occur with cooperative movement of atoms by means of lattice invariant shears on a {110} - type plane of austenite matrix which is basal plane of martensite.Copper based alloys exhibit this property in metastable β-phase field. High temperature β-phase bcc-structures martensiticaly undergo the non-conventional structures following two ordered reactions on cooling, and structural changes in nanoscale level govern this transition cooling. Atomic movements are also confined to interatomic lengths due to the diffusionless character of martensitic transformation.

Abstract: The morphology and substructure of martensite is considered to arise from the lattice invariant shear (LIS) associated with the transformation and this may be slip, twinning or both. Out of the several possible slip shears and twin modes only a few satisfy invariant plane strain criteria of the phenomenological theory of martensite (PTMC). On the basis of crystallographic and energetic criteria, a simple model has been proposed for determining the factors which influence the selection of the preferred LIS mode. In the present work, it is found that for b ® a' martensitic transformation in Zr-2.5 wt%Nb alloy, the preferred slip system is {1101}a'<2113>a' and the preferred twin system is {1101}a'<415 3>a'.