CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 5
elements, and often imparts good corrosion resistance to the base material. This approach of
corrosion protection is due to the fact that alloying elements promote passivity, alter the cathodic,
and anodic reaction rate to reduce the corrosion rate thereby offers greater scope for
understanding the criteria of alloy design from corrosion point of view. The philosophy of
selection of alloying element is based upon their ability to promote passivity by lowering the
passivation potential, increasing the breakdown potential, and lowering the passive current
density. Apart from this, sub-surface modification is important in locating specific species in the
near-surface, and examining its usefulness as well as understanding the corrosion mechanism.
Ion implantation using accelerator is widely used as a sub-surface modification technique to
modify the near-surface for improved corrosion resistance, superior mechanical, and tribological
properties [49,50, 137-139]. The ability to introduce almost all elements into the surface region
of material independent of thermodynamic constraints in precisely controlled way gives ion
implantation advantage over other high temperature diffusion process for modifying the surface.
As compared to conventional high temperature diffusion process for modifying the surface, ion
implantation does not change the bulk properties of the material. Moreover, the oxide layer
present on the surface also does not effect on the implantation process due to high energy of the
ions. It can effectively control the structure, and composition in the near-surface region for
enhancement in corrosion resistance. The improvements are attributed to amorphization of near
surface layers, change in chemical composition, and formation of certain phases depending upon
the chemical effects of the implanted ions, energy of the implanted ions, fluence rate, and the
temperature during implantation process [140-142].
In the last decade, significant efforts have been made to study the effects of nitrogen
implantation on corrosion behaviour of stainless steels due to their diversified ranges of use [21,