Corrosion Behaviour and Bioactivity of a Laser Surface Melted AISI 316L Stainless Steel
A. Kumar, S. K. Roy, S. Pityana and J. Dutta Majumdar
In the present study the corrosion behaviour and bioactivity of laser surface melted AISI 316L stainless steel has been carried out. Laser surface melting has been carried out using a 5 kW continuous wave (CW) fibre delivered Nd:YAG laser with a beam diameter of 4 mm under a varied laser power and scan speed using Ar and N2 as shrouding gas. Corrosion property has been evaluated in Hank’s solution and bioactivity has been studied by immersing it in Hank’s solution followed by measurement of weight at regular interval. Corrosion potential (Ecorr) of the laser surface melted AISI 316L stainless steel shifts towards noble direction to a value of -317 mV (SCE) and -132 mV (SCE) for laser surface melting in Ar and N2 atmosphere, respectively as compared to -708 mV (SCE) of the as-received AISI 316L stainless steel. Corrosion rate was significantly reduced to 2.2 × 10−2 mm/year and 0.4 × 10−2mm/year when laser surface melted in Ar and N2 atmosphere, respectively as compared to 12.5 × 10−2 mm/year of as-received AISI 316L stainless steel. The pitting potential was significantly increased in laser surface melted AISI 316L stainless steel to a value of 158 mV (SCE) and 269 mV (SCE) when laser melted using argon and nitrogen atmosphere, respectively as compared to -319 mV (SCE) for the as received sample. Bioactivity behaviour in terms of calcium phosphate deposition rate in Hank’s solution was also improved by laser surface melting, where, nitriding showed a superior performance. Laser surface melting also showed an improved wettability as compared to as-received AISI 316L stainless steel.
Keywords: Nd:YAG laser, AISI 316L stainless steel, laser melting, corrosion, bioactivity, bio-implant