Overcoming Metallurgical and Physical Property Mismatches in Joining Dissimilar Metals via Powder Blown Laser Beam Directed Energy Deposition

<p dir="ltr">Powder-feed laser beam directed energy deposition (DED-LB) allows for several metal powder compositions to be mixed at variable rate during manufacture. The flexibility of this process enables different alloys to be mixed and combined to vary composition and properties locationally. Elemental powders can also be used for rapid, small batch alloy development and characterization. However, the bonding of different elemental metals and alloys comes with a variety of metallurgical and physical restrictions. Dissimilar metal bonds can be susceptible to intermetallic phase formation and solidification cracking across manufacturing methods. DED-LB also faces unique challenges due to the high cooling rates and short solidification time spans intrinsic to the process. Large differences in thermal and physical properties can lead to cracking from residual stress, heterogeneity in melt pools, and un-melted powder present after deposition. </p><p dir="ltr">In the first study, phase diagrams are used to avoid compositions that are prone to cracking due to intermetallic phases when joining stainless steel 304L and Inconel 625. Solidification cracking models are then evaluated to determine the accuracy of their crack susceptibility predictions, based on experimental cracking data. In the second study niobium and tantalum, two fully miscible metals with large differences in melting temperature and density, are deposited in various compositions and inhomogeneous melt pool features are analyzed. The degree of each inhomogeneity is related to the processing parameters. The focus of the third study is the elimination of unmelted powder particles, an inhomogeneity discussed in the second study. The powder stream of the DED-LB machine is characterized and melt pool temperatures are measured to determine a criterion for the elimination of unmelted powder particles based on the temperature of the melt pool. In each study, single laser passes with powder, called single tracks, are deposited and analyzed to build the framework for successful dissimilar metal bonds.</p>