Detecting hydrogen distribution at micro- and nano-scale is important for understanding the mechanisms of hydrogen embrittlement in metals. In this study, scanning Kelvin probe force microscopy (SKPFM), which can detect the variation of surface contact potential difference (CPD) caused by hydrogen, is applied to investigate the hydrogen distribution and evolution in thermally hydrogen-charged (HC) super duplex stainless steel. The SKPFM observations reveal that the CPD distribution becomes nonuniform in both the ferrite and austenite phases after hydrogen charging, implying that hydrogen distributes heterogeneously in the two phases. The average CPDs of both the ferrite and austenite phases are significantly decreased and the difference of CPD between two phases reaches a maximum shortly after thermal hydrogen-charging. The average CPDs of both the ferrite and austenite phases recover and the difference of CPD between two phases is decreased upon release of the hydrogen. These results are discussed in terms of the hydrogen outgasing behavior and the difference of hydrogen diffusivity in the two phases.

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