  Metallic materials, especially steel, underpin transportation technologies.
High-manganese twinning induced plasticity (TWIP) austenitic steels exhibit
exceptional strength and ductility from twins, low-energy microstructural
defects that form during plastic loading. Their high-strength could help
light-weighting vehicles, and hence cut carbon emissions. TWIP steels are
however very sensitive to hydrogen embrittlement that causes dramatic losses of
ductility and toughness leading to catastrophic failure of engineering parts.
Here, we examine the atomic-scale chemistry and interaction of hydrogen with
twin boundaries in a model TWIP steel by using isotope-labelled atom probe
tomography, using tritium to avoid overlap with residual hydrogen. We reveal
co-segregation of tritium and, unexpectedly, oxygen to coherent twin
boundaries, and discuss their combined role in the embrittlement of these
promising steels.
