In a newly introduced manufacturing process of nickel-free austenitic stainless steels with nitrogen absorption treatment [1], small devices can be precisely machined in a ferritic phase and than during nitrogenization of their surfaces in nitrogen gas at temperature approx. 1200^oC they become nickel-free austenitic stainles steels with better mechanical and corrosion resistance properties.

Using the combination of mechanical alloying (MA), heat treatment and nitrogenation of elemental microcrystalline Fe, Cr, Mn and Mo powders it is possible to syntesize a nanocrystalline nickel-free stainless steels. Nanocomposites with addition of hydroxyapatite have been prepared for the best samples The process parameters, morphology, microhardness and EDX-analysis of obtained powders were determined. Phase transformation from ferritic to austenitic was confirmed by XRD analysis. Changes of size and shape of the mechanically alloyed powder mixtures as a function of milling time was done by the SEM and AFM techniques. Human normal diploid fibroblasts were cultured onto each disk of nanostructured steels. Also 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.

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 [2]. The results show that nanocrystalline nickel-free stainless steels and 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.

[1] M. Sumita et al.: Materials Science and Engineering C 24 (2004) 753

[2] Edelstain A.S., Murday J.S., Rath B.B.: Prog. Mater. Sci., 42 (1997) 5

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1. Hybrid Ti-ceramic bionanomaterials for medical engineering
2. Mechanical and corrosion properties of titanium – hydroxyapatite nanocomposites
3. Mechanical and corrosion properties of Ni-free austenitic stainless steel/hydroxyapatite nanocomposites
4. Nanoscale nickel-free austenitic stainless steel