Abstract
AbstractIn a newly introduced manufacturing process of nickel‐free austenitic stainless steels with nitrogen absorption treatment (M. Sumita et al., Mater. Sci. Eng. C 24, 753 (2004) [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 °C 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 synthesize a nanocrystalline nickel‐free stainless steels. Nanocomposites with addition of hydroxyapatite (HA) have been prepared for the best samples. Phase transformation from ferritic to austenitic was confirmed by XRD analysis. 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 nitriding. Mechanical alloying and nitriding are very effective technologies 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 (A.S. Edelstain et al., Prog. Mater. Sci. 42, 5 (1997) [2]). The results show that from mechanical and corrosion properties point of view nanocrystalline nickel‐free stainless steels and nickel‐free stainless steel/hydroxyapatite nanocomposites could be promising bionanomaterials for use as a hard tissue replacement implants, e.g. orthopedic implants. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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