Heterogeneous nucleation of martensite near free surface

A theoretical model is proposed which describes heterogeneous nucleation of an embryo of hcp-martensite near a free surface at a tilt grain boundary s egment containing some extrinsic dislocations. The total energy gain due to the hep-embryo nucleation is analysed in detail depending on internal (the distance from free surface and orientation of the grain boundary plane) an d external (the temperature and shear stress) conditions. It is shown that the main characteristics of the hcp-embryo nucleation (the energy barrier a nd critical size) depend strongly on the distance from the free surface. (C ) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights r eserved.