Which hardness (nano or macrohardness) should be evaluated in cavitation?

This paper is concerned with the analysis of data obtained from instrumented depth-sensing nanoindentation testing performed on materials whose hardness varies with depth from surface. The objective is to determine which hardness (nano or macrohardness) should be evaluated in functionally graded materials to correlate the material properties to its performance in cavitation. A linear relationship between H2/E and cavitation erosion resistance could be established. Significant improvements in the cavitation erosion resistance can be achieved when deep nitrided cases are present.