Phase-specific elastic/plastic interface interactions in layered NiAl–Cr(Mo) structures

The depth-dependent, as-grown and deformation-induced strain and dislocations partitioned through the interfaces in a two-phase layered NiAl–Cr(Mo) structure are directly measured at the mesoscale using 3-D X-ray microdiffraction. It is demonstrated that in the as-grown, undeformed state, neighboring submicron Cr solid solution and NiAl eutectic lamellae (doped with ～3% Mo) form a heterointerface with 180° rotation around a 〈1 1 2〉 pole. It is shown that the mechanical response to the indentation of a layered composite with alternating Cr(Mo)–NiAl lamellae is distinct from the response of single-phase materials. In the center of the indent, after the load is released, the NiAl lamellae are under compressive forward stresses (with the same sign as the indentation-induced compression) while Cr solid solution lamellae are under tensile back stresses (with opposite sign from the indentation load). The depth-dependent alternation of compressive/tensile residual strains in the neighboring Cr solid solution and NiAl lamellae is understood in the framework of the Mughrabi’s composite model considering two types of structure elements: harder and softer regions. Under indentation, both kinds of lamellae are assumed to deform compatibly. After the load is released, residual forward stresses are formed in the harder lamellae, and back stresses are formed in the mechanically softer lamellae. Line-broadening analysis of the intensity distribution along the diffraction vector reveals a 15-times increase in dislocation density in the near-surface zone in the center of the indent. Such a large increase is typical for severe deformation.     

Microscopic Deformation in Individual Grains in an Advanced High-Strength Steel

In situ synchrotron microbeam x-ray diffraction experiments were carried out to study the microscopic deformation within individual ferrite grains in a martensite/ferrite dual-phase steel (DP980) under incremental tensile loading. The differential aperture x-ray microscopy technique was used to resolve the strain variations as a function of depth up to 100 μm deep from the sample surface. The highly inhomogeneous distributions of the lattice strain, which is associated with the elastic deformation and stresses inside the grains, were determined by means of monochromatic energy diffraction, whereas insights to the plastic deformation were revealed by polychromatic energy diffraction.     

Submicron position-sensitive detector

A method has been developed to measure precisely the coordinates of charged particles incident between adjacent strips of a strip detector. The position sensitivity of an inter-strip gap has been studied by means of a pulsed laser beam and irradiation by -particles of a ²²⁶Ra-source. The capacitive division of charge generated by the incident particle depends on the position of its track. Its coordinates were determined by two-dimensional amplitude analysis of the charges collected by neighbouring strips. This method of coordinate determination applied to studies of spatial and energy distributions of electromagnetic as well as charged particle beams (including radioactive ion beams) of low intensity could provide the highest level of the precision limited by the track dimensions of charged particles, i.e. percents of a micrometer.