Recently, a new manufacturing process of nickel-free austenitic stainless steels with nitrogen absorption treatment has been developed. In this method, small devices can be precisely machined in a ferritic phase and than during nitrogenization of their surfaces in nitrogen gas at temperature approx. 1200oC they become nickel-free austenitic stainles steels with better mechanical and corrosion resistance properties.
In the present work, a nanocrystalline nickel-free stainless steels as well as nickel-free stainless steel/hydroxyapatite nanocomposites has been synthesized by the combination of mechanical alloying (MA), heat treatment and nitrogenation of elemental microcrystalline Fe, Cr, Mn and Mo powders. Phase transformation from ferritic to austenitic was confirmed by XRD analysis.
The microhardness of the final bulk material was studied using Vickers method. The result is almost two times greater than in austenitic steel obtained by conventional methods. This effect is directly connected with structure refinement and obtaining of nanostructure.
Mechanical alloying is a very effective technology to improve also the corrosion resistance of stainless steel. Decreasing the corrosion current density is a distinct advantage for prevention of ion release and it leads to better cytocompatibility. Corrosion tests were performed in Ringer’s solution.
According to existing conceptions, decreasing of material’s crystallites size to nanometric scale allows to achieve much better mechanical properties (e.g. microhardness) compared to conventional materials. With regard to austenitic stainless steels it could help to obtain better biomedical implants (e.g. stents) with better mechanical properties, corrosion resistance and biocompatibility.
The results show that nickel-free stainless steel/hydroxyapatite nanocomposites could be promising bionanomaterials for use as a hard tissue replacement implants from mechanical and corrosion properties point of view.