Indentation size effect: large grained aluminum versus nanocrystalline aluminum-zirconium alloys

• Published in: Scripta materialia Vol. 43; no. 10; pp. 951 - 955
• Main Authors: Elmustafa, A.A, Eastman, J.A, Rittner, M.N, Weertman, J.R, Stone, D.S
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Ltd 30.10.2000; Elsevier Science
• Subjects: ALLOYS; ALUMINIUM; Aluminum; Applied sciences; Condensed matter: structure, mechanical and thermal properties; Contact stiffness; Deformation and plasticity (including yield, ductility, and superplasticity); Exact sciences and technology; GRAIN SIZE; Hardness; Indentation size effect; MATERIALS; MATERIALS SCIENCE; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Metals. Metallurgy; Nanocrystalline aluminum-zirconium; Nanoindention; Physics; ZIRCONIUM; Nanoindention; Nanocrystalline aluminum-zirconium; Contact stiffness; Indentation size effect; Hardness; Aluminum; Binary alloys; Aluminium base alloys; Coarse grain structure; Aluminium; Plastic properties; Hardness indentation; Nanostructures; Experimental study; Indentation; Nanostructured materials; Zirconium alloys
• ISSN: 1359-6462; 1872-8456
• DOI: 10.1016/S1359-6462(00)00520-0

Some materials exhibit an increase in the hardness with decreasing load; this is called the indentation size effect, or ISE. Other materials undergo a decrease in the hardness with decreasing load; this is referred to as the reverse indentation size effect, or RISE. This work investigates the use of the ISE in high-purity aluminum and nanocrystalline aluminum-zirconium alloys. Hardness is characterized using both microhardness and nanoindentation. With nanoindentation, the hardness for indents at depths below 1.0 micron were able to be determined. The nanoindentation also allowed the authors to directly address the problem of measurement capability by relying on contact stiffness to determine the projected contact area rather than relying on optical images or depth of indentation alone (Elmustafa and Stone, 1999). An ISE was observed in the polycrystalline aluminum with a grain size of 55 microns. An ISE was not observed in the nanocrystalline aluminum-zirconium alloy. It appears that the lack of an ISE in thin films with ultrafine microstructure is also observed in bulk material with ultrafine microstructure. It is concluded that it is the small grain size that inhibits the ISE. (CSA)