Effects of bath composition and processing conditions on the microstructure and mechanical properties of coatings developed on 316 LVM by hot dipping in melted AlSi alloys

Austenitic stainless steel 316 LVM (Low Vacuum Melting) is typically used in biomedical applications. However, its biocompatibility has always been in controversy since the passive film developed on the surface can release metallic ions (Ni2+, Cr3+ and Cr6+), which may cause local systemic effects into the human body and therefore, the premature failure of implant as result of inflammatory reactions. This is one of the driving forces to design new coatings with enhanced biocompatibility and bioactivity. The goal of this work is to develop novel intermetallic coatings grown on the 316 LVM steel by hot dipping in melted AlSi alloys. The Si content of the bath and the processing conditions have been found to be fundamental to control the morphology, microstructure and mechanical properties of the coatings. Nature of the coating consist of a mixture of intermetallic Al3FeSi2 + Al17.5Fe4Si1.5 phases and Al3FeSi2 + (Si,Al)(2)Cr for the Al-12Si and Al-25Si baths, respectively. Interestingly, the coatings are Ni-free and exhibit an elevated hardness (similar to 6 GPa) and lower Young's modulus (similar to 160 and similar to 170 GPa, respectively) than stainless steel (similar to 210 GPa). These mechanical properties result very useful to study the elastic-plastic transition through the plasticity index (PI), which correlates the hardness and Young's modulus with the elastic energy of these surfaces. These values are lower than the substrate and therefore, these intermetallic coatings may be considered good candidates for biomedical applications where surfaces with load transfer capacity higher than that of the stainless steel are needed. (C) 2014 Elsevier B.V. All rights reserved.