  Defects and microstructural features spanning the atomic level to the
microscale play deterministic roles in the expressed properties of materials.
Yet studies of material evolution in response to environmental stimuli most
often correlate resulting performance with one dominant microstructural feature
only. Here, the dynamic evolution of swelling in a series of Ni-based
concentrated solid solution alloys under high-temperature irradiation exposure
is observed using continuous, in situ measurements of thermoelastic properties
in bulk specimens. Unlike traditional evaluation techniques which account only
for volumetric porosity identified using electron microscopy, direct property
evaluation provides an integrated response across all defect length scales. In
particular, the evolution in elastic properties during swelling is found to
depend significantly on the entire size spectrum of defects, from the nano- to
meso-scales, some of which are not resolvable in imaging. Observed changes in
thermal transport properties depend sensitively on the partitioning of
electronic and lattice thermal conductivity. This emerging class of in situ
experiments, which directly measure integrated performance in relevant
conditions, provides unique insight into material dynamics otherwise
unavailable using traditional methods.
