Effect of loading/unloading rate on instrumented indentation measurements in alloy Cu-2%Be

Abstract

The influence of the loading/unloading rate on the indentation strain rate, hardness and elastic modulus in Cu-2wt%Be samples subjected to different aging treatments was analyzed. Homogenized samples were aged for 1 and 10 h at 400 °C to induce the formation of γ′ and γ precipitates, and instrumented indentation tests were performed at different loading rates between 0.15 and 1 mN s−1. The indentation curves of all the samples were influenced by the loading/unloading rate, but the behavior of the samples with precipitates was different from that of the homogenized samples. Strain rate levels during loading were also influenced by the loading rate. The strain rate increased almost linearly with the loading rate in the homogenized sample and the sample with γ′ nanoprecipitates, while it experienced a decelerated increase with the loading rate in the sample with γ phase. The hardness and reduced modulus were estimated from the indentation curves using the Oliver and Pharr method. Hardness remained almost constant at approximately 2.4 GPa as the rate was varied in the homogenized sample. On the other hand, the samples with γ′ and γ phase exhibited higher hardness values at 0.15 mN s−1, while it remained approximately constant for the other rates. The reduced modulus increased with the loading/unloading rate and this increase was more pronounced for the sample with γ precipitates, with a higher sensitivity of the reduced modulus increase.