for combining information from multiple precipitates within a single data set (40). In this work,
we selected all the carbides incorporating more
than 100 total ions, and then computed the radius of gyration normal to z for the particles (rg).
We collected composition profiles from each particle (and surrounding matrix) along the z axis of
the particle (four times the particles’ full z bounds),
using a square aperture of length 2rg. We normalized the profile’s z distance to 0–1 (0 → start of
particle, 1 → end of particle along z). Last, we
accumulated the profiles to form a single combined composition profile (Fig. 3), in which we
observed that the deuterium is restricted to the
interior of the carbide, where it reaches a maxima
before decaying. If hydrogen was restricted to the
interfacial region at the surface, we would have
found a U-shaped profile, which is clearly not
the case in the data presented here.
These results are consistent with neutron scat-
tering results, such as given by Malard et al. (17),
who undertook charging using a 0.1 M NaOH
solution. In their work, they observed a change
in the neutron scattering data after hydrogen-
charging a steel that contains VC. However, this is
in contrast with the neutron scattering work of
Ohnuma et al. (39) on a steel containing NbC
precipitates, where it was suggested that hy-
drogen is present at the interface. Malard et al.
estimated that at most, 5 parts per million weight
of hydrogen was contained within the precip-
itates, which given their volume fractions corre-
sponded to 10 atomic (at %) H contained in the
precipitate. In our work, we found a peak deute-
rium concentration of 0.6 at and an average
concentration of 0.01 ± 0.0025% (counting error,
2 SD). However, this may be underestimated from
the as-charged condition, owing to diffusion dur-
ing the transfer from the charging unit to the
These results are critical to further understand-
ing the role of hydrogen within steel micro-
structures; however, the technique is not limited
to these materials. Other trapping sites, such as
grain and phase boundaries, may prove impor-
tant in the design of hydrogen-resistant materials,
and this approach has the potential to provide
new insight. Furthermore, the method may prove
useful elsewhere; systems that may be of interest
include nickel superalloy materials, titanium al-
loys, and austenitic steels, in which hydrogen may
play an important role in determining macro-
scopic mechanical properties. We believe that
the approach demonstrated here, using liquid
charging and cryogenic transfer, is a valuable tool
in understanding hydrogen embrittlement from
a microstructural perspective.
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Fig. 3. Combined analysis of deuterium-charged carbides. Superimposed profile of carbides,
generated by normalizing and combining multiple individual profiles from each VC (>100 atoms).
Resultant profile shows deuterium within the carbide, at ≈0.5 at concentration. Atom map shows
≈10-nm slice through the data set.