Superhard Nanocrystalline Homometallic Stainless Steel on Steel for Seamless Coatings

The objective of this work is to deposit nanocrystalline stainless steel onto steel substrates (homometallic) for enhanced wear and corrosion resistance. Homometallic coatings provide superior adhesion, and it has been shown that ultrafine-grained materials exhibit the increased hardness and decreased permeability desired for protective coatings. Recently we have demonstrated, for the first time, that nanocrystalline (3-40 nm grains) Co-Cr deposited onto Co-Cr-Mo substrates possesses hardness close to that of some ceramics (18-26 GPa, 400% increase), without the associated problems with adhesion to metallic substrates. Our preliminary results also show fabrication of nanocrystalline (<40 nm crystals) Ti with hardness of 12-14 GPa, which is comparable with the hardness of zirconia. Nanocrystals have been achieved by controlling nucleation and growth and use of an ion beam-plasma during deposition by e-beam evaporation or sputtering.Phase I work will deposit nanocrystalline stainless steel onto stainless steel substrates. It is expected that these coatings will exhibit hardnesses comparable to those normally obtained for ceramic coatings, and possess the superior adhesion of seamless, homometallic coatings. Hardening the surface with a similar material will also enhance adhesion, by avoiding problems associated with thermal and lattice mismatch.The aim of Phase I is to fabricate nanocrystalline stainless steel coatings with a significant improvement in hardness and wear resistance, and to demonstrate the advantage of nanocrystalline protective coatings. Phase II will extend the work to the deposition of other nanocrystalline homometallic coatings, such as Ti-6Al-4V.