Interfacial Strength Evaluation Between Sulfur-Segregated Al2O3 and Ni–Al Single Crystal Alloy Using Nanoindentation

Ni-base superalloysNi-base superalloys have excellent oxidationOxidation resistance, but impurityImpurity S drastically decreases their properties. This is due to the segregationSegregation of S to the oxide/substrate interface, but direct and quantitative measurements of the interfacial strengthInterfacial strength in relation to the S segregationSegregation level have not been widely conducted. The objective of this research is to quantitatively analyze the interfacial strengthInterfacial strength between the Al2O3 layer and Ni-base substrate, depending on the S segregationSegregation level, using nanoindentationNanoindentation. Ni-9.8 wt.% Al alloys were prepared by melting the material using either an Al2O3 crucible (high Sinterface alloy) or a CaOCaO crucible (low Sinterface alloy). NanoindentationNanoindentation tests using a 60 degree pyramidal diamond indenter were conducted, and the cross-sections of both specimens exposed the (100) plane. Indentation near the interface formed cracks at the boundary between the two layers, which can be observed as pop-in events in the load-depth curves. The amount of load at the initial pop-in most likely represents the interfacial strengthInterfacial strength between the Al2O3 layer and Ni-base substrate. A Weibull analysis of results showed that suppression of the S segregationSegregation level increased the critical β scale parameter for crack formation by 650 μN. This suggests that we were able to successfully compare the effect of S segregationSegregation on the interfacial strengthInterfacial strength between the Al2O3 layer and the Ni-base substrate quantitatively.