Combining synchrotron X-ray diffraction, mechanistic modeling and machine learning for subsurface temperature quantification during laser melting.

Laser melting, such as that encountered during additive manufacturing, produces extreme gradients of temperature in both space and time, which in turn influence microstructural development in the material. Qualification and model validation of the process itself and the resulting material necessitate the ability to characterize these temperature fields. However, well established means to directly probe the material temperature below the surface of an alloy while it is being processed are limited.

High-speed X-ray imaging of the Leidenfrost collapse.

The Leidenfrost layer is characterized by an insulating vapor film between a heated surface and an ambient liquid. The collapse of this film has been canonically theorized to occur from an interfacial instability between the liquid and vapor phases. The interfacial instability alone, however, is insufficient to explain the known influence of the surface on the film collapse process.

Microyielding of core-shell crystal dendrites in a bulk-metallic-glass matrix composite.

In-situ synchrotron x-ray experiments have been used to follow the evolution of the diffraction peaks for crystalline dendrites embedded in a bulk metallic glass matrix subjected to a compressive loading-unloading cycle. We observe irreversible diffraction-peak splitting even though the load does not go beyond half of the bulk yield strength. The chemical analysis coupled with the transmission electron microscopy mapping suggests that the observed peak splitting originates from the chemical heterogeneity between the core (major peak) and the stiffer shell (minor peak) of the dendrites.

Fatigue-induced damage in Zr-based bulk metallic glasses.

In the present work, we investigate the effect of "fatigue" on the fatigue behavior and atomic structure of Zr-based BMGs. Fatigue experiments on the failed-by-fatigue samples indicate that the remnants generally have similar or longer fatigue life than the as-cast samples. Meanwhile, the pair-distribution-function (PDF) analysis of the as-cast and post-fatigue samples showed very small changes of local atomic structures.