Nanomechanical testing of in situ hydrogen charged high strength steel

Abstract

The effect of finely dispersed titanium carbides on the nanomechanical behavior of high strength steel in the presence of hydrogen has been investigated. Nano sized pillars have been milled from steel samples using a Focused Ion Beam at the NTNU Nanolab. These have been compressed both in air and with in situ charged hydrogen. The resulting stress-strain curves have been extracted and compared against each other. An effect of hydrogen was found in martensitic phases, with the titanium carbide-containing sample showing less hydrogen damage than the sample without titanium. The same tests performed in the ferritic phase in specifically-chosen grains displayed no hydrogen effect on the yield strength, but in both cases the effect of hydrogen was observed in the increase of strain hardening for the titanium carbide-containing samples. A method for switching charging potentials during compression of a single nanopillar was developed, tested, and showed the effect of hydrogen on both samples, without a clear reduction for the titanium carbide-containing sample.