Solidification Diagnostics for Joining and Microstructural Simulations

Abstract

Solidification is an important aspect of welding, brazing, soldering, LENS fabrication, and casting. The current trend toward utilizing large-scale process simulations and materials response models for simulation-based engineering is driving the development of new modeling techniques. However, the effective utilization of these models is, in many cases, limited by a lack of fundamental understanding of the physical processes and interactions involved. In addition, experimental validation of model predictions is required. We have developed new and expanded experimental techniques, particularly those needed for insitu measurement of the morphological and kinetic features of the solidification process. The new high-speed, high-resolution video techniques and data extraction methods developed in this work have been used to identify several unexpected features of the solidification process, including the observation that the solidification front is often far more dynamic than previously thought. In order to demonstrate the utility of the video techniques, correlations have been made between the in-situ observations and the final solidification microstructure. Experimental methods for determination of the solidification velocity in highly dynamic pulsed laser welds have been developed, implemented, and used to validate and refine laser welding models. Using post solidification metallographic techniques, we have discovered a previously unreported orientation relationship between ferrite and austenite in the Fe-Cr-Ni alloy system, and have characterized the conditions under which this new relationship develops. Taken together, the work has expanded both our understanding of, and our ability to characterize, solidification phenomena in complex alloy systems and processes.

Porosity in millimeter-scale welds of stainless steel : three-dimensional characterization.

“…Later work [5] focused on providing understanding and corrective measures for related effects of laser welding, such as shape distortions. By the mid-2000's Sandia began integrating modeling heavily into investigations to more accurately determine the fundamental heat :: material interaction over a variety of laser and GTA welding processes [6][7][8][9][10] . While not an exhaustive list, the aforementioned do highlight the progression of Sandia's publicly available work in the field.…”