E-catalog        

Библиогр.: 64 назв.

Microstructural elements in NiTi shape memory alloys (SMAs) e precipitates, phase boundaries, inclusions,
grain boundaries e can be viewed as sources of multiscale constraint that influence their
deformation response. We characterized in situ, and in 3D, the deformation and the evolution of
microstructure during a tension test in a superelastic NiTi specimen containing some of these sources of
constraint. The method used was far-field high-energy X-ray diffraction microscopy (ff-HEDM), complemented
by electron microscopy. We simulated the local stress state in the specimen using a microstructural
model informed by the experimental data. Using these combined microstructure, deformation,
and stress data, we report three phenomena, and relate them to specific sources of constraint. During
initial elastic loading, axial lattice strain in austenite increased monotonically. On partial stress-induced
phase transformation to martensite, the stress redistributed to both phases leading to a stress relaxation
in austenite. The specimen contained a dense distribution of inclusions, which led to the activation of
martensite habit plane variants that produce less than theoretical maximum transformation strain. Large
Ni4Ti3 precipitates potentially contributed to the poor transformation response. Under load, proportional
gradients in local rotation and elastic stretch developed in the martensite phase, because of the
constraint at phase interfaces. This combined ff-HEDM, electron microscopy, microstructural simulation
toolbox provides a versatile method to understand the effect of constraint on inelastic deformation in
other alloys with hierarchical microstructure