DETERMINATION OF INDENTER TIP GEOMETRY AND INDENTATION CONTACT AREA FOR DEPTH-SENSING INDENTATION EXPERIMENTS

The phenomena of pile-up and sink-in associated with nanoindentation h ave been found to have large effects on the measurements of the indent ation modulus and hardness of copper. Pile-up (or sink-in) leads to co ntact areas that are greater than (or less than) the cross-sectional a rea of the indenter at a given depth, These effects lead to errors in the absolute measurement of mechanical properties by nanoindentation. To account for these effects, a new method of indenter tip shape calib ration has been developed; it is based on measurements of contact comp liance as well as direct SEM observations and measurements of the area s of large indentations, Application of this calibration technique to strain-hardened (pile-up) and annealed (sink-in) copper leads to a uni que tip shape calibration for the diamond indenter itself, as well as to a material parameter, cu, which characterizes the extent of pile-up or sink-in. Thus the shape of the indenter tip and nature of the mate rial response are separated in this calibration method. Using this app roach, it is possible to make accurate absolute measurements of hardne ss and indentation modulus by nanoindentation.