A KINETIC STUDY OF THERMOCHEMICALLY BORIDED AISI 316L STAINLESS STEEL

Abstract

Biomaterials are used in different parts of human body as replacement implants in medical applications. An implant material should have high biocompatibility, corrosion and wear resistance, and suitable mechanical properties in terms of safety and long-service period. There are only a few biocompatible implant materials: AISI316L stainless steel is one of the materials used in this type of applications. They have relatively poor wear resistance. Boriding being a thermochemical diffusion treatment is one of the processes to improve their wear resistance. Borides are formed by introducing boron atoms by diffusion onto a substrate surface and they are non-oxide ceramics and could be very brittle. The growth kinetics of boride layer is analyzed by measuring depth of layers as a function of boriding time within a temperature range. In this study, the effects of Ekabor-2 bath on formation mechanism and properties of boride layer in thermochemical diffusion boriding of AISI316L stainless steel were investigated. Different temperatures and durations were applied in boriding operations and hardness, optical microscopy, XRD, EPMA and SEM studies were performed to detect the properties of boride layers. It was found that thickness of boride layer increased with increasing temperature and time; the basic phase in the boride layer formed was Fe2B and FeB phase also formed. It was also found that surface hardness values of borided materials increased depending on temperature and time of boriding process; surface hardness values of borided materials are approximately 10 times higher than surface hardness values of non-borided AISI316L stainless steel and formation activation energy of boride layer is 149.3 kjmol-1.