In Situ Characterization of Hot Cracking Using Dynamic X-Ray Radiography

We employ dynamic X-ray radiography (DXR) for in situ and real-time characterization of the hot cracking phenomenon for aluminum alloy 6061 under the processing conditions typical of laser powder bed fusion. The dynamics of processes such as a crack initiating from a bubble trapped subsurface are captured. We also directly observe the backfilling of liquid that heals an open crack. In addition, we demonstrate the feasibility of determining the point of origin for hot cracking with a temporal resolution of order 20 µs and spatial resolution of order 2 µm. This could shed light on the estimation of solid fraction at the initiation of hot cracking, which is a critical parameter upon which many models are based. We demonstrate the capability of DXR for generating new insights into verify or refine hot cracking models, and understand this problem fundamentally, which could ultimately lead to the optimization of process control for additive manufacturing.