The significance and challenges on determining the size-effect of indentation hardness at nano-scale
Abstract
<p indent="0mm">Instrumented indentation is a method that has been widely used to obtain material properties at micro and nano scale, yet creditable indentation size effect at real nano-scale and its mechanism are still unsolved. This paper summarizes our recent work on progresses in experimental and simulation approaches to this problem. By confirming the crystalline orientations and the surface roughness of the sample, obtaining the tip radius of the indenters, as well as considering tip radius in large-scale molecular simulation, the gap between the experiment and simulation results is bridged, and these two results can be cross verified with each other, which leads to a reliable hardness trend over the indentation depth at nano-scale. Two opposite size effects are observed, and their different mechanisms are revealed, as the conventional size effect results from the plastic behavior such as dislocation nucleation and propagation in the sample beneath the indenter, while the initial reverse size effect is due to the combined effect of the indenter roundness and elastic behavior of the material. Systematic investigation on the efficiency and fidelity of MD and MS is carried out, on problem of the dislocation evolution during indentation, the influence of the relaxation time and convergence resolution on the load curve and dislocation patterns are studied, and suggestion on choice of two simulation methods and the relaxation time and convergence resolution are given. </p>
