Nanostructured surfaces

The analysis of properties of surface nanocrystalline structures by the method of nanoindentation
O.V. Maksymiv, V.I. Kyryliv, H.M. Nykyforchyn
Karpenko Physico-Mechanical Institute of NAS of Ukraine, Lviv
Naukova str., 5, Lviv, 79060, Ukraine.
okyryliv@yahoo.com

Nanostructured materials frequently possess changed basic characteristics such as modulus of elasticity, Cuire and Debye temperatures, saturation magnetization, etc. which usually are structurally insensitive. Elastic properties of the solid states are usually determined by the character of interatomic interaction. From the other hand, the mechanical properties are determined by elastic characteristics. Therefore, the analysis of elastic properties of nanocrystalline structures (NCS) received by severe plastic deformation (SPD) is the matter of great scientific and practical importance. It reveals new possibilities to improve existent and creation of new materials with prespecified properties. 
The technology of mechanical-pulse treatment (MPT) is developed and used to form gradient NCS on the component’s surface by SPD generated by high-speed friction. The analysis of physical properties of the surface NSC on 40Kh (0.4C, 1Cr) and U8 (0.8C) steels were carried out using nanoindentor «Micron-gamma». Special attention was paid to estimation of modulus of elasticity by the method of continuous indentation of diamond indentor based on automatic registration of the load on indentor and the depth of its penetration. The results are represented as load diagrams which allow estimating surface microhardness and elasticity of materials. The methodological basics of estimation of microhardness and modulus of elasticity using load diagrams are based on Oliver and Pharr [1] method which is accepted as international standard ISO 14577.
It was showed that nanostructurisation of U8 steel leads to increasing of modulus of elasticity from 230 to 270 GPa. The roughness of the NCS surface is also improved at the appropriate treatment regimes, what is confirmed of 3D images of the surface.

1.	Oliver W. C., Pharr G. M. An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation measurements // J. Mater. Res. – 1992. – 7, N 6. – P. 1564-1583.