Hardness-depth profiling on nanometer scale

Abstract

Three methods for hardness-depth profiling were applied to a 200-nm-thick TiC film deposited onto a Ti-6Al-4V substrate. The methods were evaluated and compared with regard to their ability to detect local changes in hardness with a depth resolution on the order of a few nanometers. In the cross section method (CSM), the indentations are performed on a cross section of the sample, i.e., in a direction perpendicular to the hardness gradient. In the load-variation method (LVM) and in the constant-load method (CLM), the indentations are made in the direction of the hardness gradient, i.e., perpendicular to the as-prepared surface. In the LVM, the hardness-depth profile is assessed using a stepwise increase of the maximum load applied to the surface. In the CLM, sublayers are removed successively by ion sputtering and hardness measurements are performed at each newly exposed surface using the same low maximum load. The CSM revealed a nearly constant hardness across the TiC film and a sharp transition from the TiC film to the Ti-6Al-4V substrate. The hardness profile obtained using the LVM and the CLM is smeared out because the recorded response is due to both the TiC film and the underlying softer Ti-6Al-4V substrate.