Apparent indentation size effect in a CVD aluminide coated Ni-base superalloy

Indentation hardness testing was used to assess the mechanical properties of a low activity CVD β-NiAl bond coat applied to a single crystal Ni-base superalloy substrate. Tests performed in the nano- and micro-hardness regimes using a Knoop indenter geometry revealed the presence of an indentation size effect (ISE) where the apparent hardness increased significantly with decreasing indentation test load. An energy balance analysis was applied to analyze the apparent ISE and to extract the load independent hardness from the experimental measurements. The energy balance model could not be successfully applied to the nanoindentation data. This is attributed in part to blunting of the nanoindenter tip, which resulted in changes in indenter contact area.