Characterization of the Mechanical Properties of Surface Nanocrystallized Materials

Recrystallization of the grain structure of metals into nano-sized grains by using mechanical means, has received wide attention in the last two decades. It is well known that materials with a fine-grain crystal structure have favorable properties compared to the same materials with course-grained crystal structure. Surface Mechanical Attrition Treatment (SMAT), a technique developed in the early part of this decade, has been successfully used to recrystallize the surface grains of metals into nanocrystals of the order of 10 to 100 nanometers from their original grain sizes on the order of 10 to 30 microns. Resulting enhancement in surface properties has quite interesting applications, varying from materials with improved fatigue resistance to medical devices. In this study, our focus is on experimental characterization of the enhancement in mechanical properties of surface nanocrystallized metals. Copper, Aluminum and Titanium samples are subjected to SMAT under different conditions followed by appropriate heat treatment. Microindentation and nanoindentation techniques are conducted to characterize various mechanical properties. Microindentation test shows significant improvement in surface hardness due to SMAT process on these samples. Our initial results from nanoindentation also show significant enhancement in materials surface properties. However, several other interesting characteristics obtained in the nanoindentation tests require further studies for verification.