Assessment of Hydrogen-Induced Precipitation in a Nickel-Copper Alloy Using Thermoelectric Power

Hydrogen sensing using thermoelectric power (TEP) was performed on a nickel-copper alloy to assess the hydrogen content resulting from cathodic protection. The measured TEP as a function of hydrogen content developed an anomaly at a specific hydrogen content, indicating a hydrogen-induced phase transformation in the alloy. The formation of Ni₂H phase was found in a hydrogen-charged alloy (UNS N05500) using x-ray diffraction (XRD). The transmission electron microscopy (TEM) investigation of the hydrogen-charged alloy specimen revealed nano-sized Ni₂H participates dispersed in the nickel-copper matrix. The measured TEP profile correlated with an alloy hydride phase formation on a hydrogen-metal pressure-composition-temperature (PCT) activity diagram. These results indicate that the TEP surface contact probe measurements can assist in the nondestructive evaluation (NDE) identification of a microstructural change in hydrogen-charged nickel-copper alloys. With this TEP surface probe measurement technique, in situ determination of the susceptibility of an alloy to hydride formation is possible.