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Purpose Directed energy deposition (DED) with laser powder-feed is an additive manufacturing process that is used to produce metallic components by simultaneously providing a supply of energy from a laser and mass from a powder aerosol. The breadth of alloys used in DED is currently limited to a very small range as compared to wrought or cast alloys. The purpose of this paper is to develop the new alloys for DED is limited because current models to predict operational processing parameters are computationally expensive and trial-and-error based experiments are both expensive and time-consuming. Design/methodology/approach In this research, an agile DED model is presented to predict the geometry produced by a single layer deposit. Findings The utility of the model is demonstrated for type 304 L stainless steel and the significance of the predicted deposition regimes is discussed. The proposed model incorporates concepts from heat transfer, welding and laser cladding; and integrates them with experimental fits and physical models that are relevant to DED. Originality/value The utility of the model is demonstrated for type 304 L stainless steel and the significance of the predicted deposition regimes is discussed.

Feasibility tests were performed by manufacturing transition joints between Nickel-200 (Ni-200) and Alloy K-500 (K-500) with direct laser deposition. Both sharp and functionally graded interfaces were manufactured with no apparent issues. In addition, Alloy K-500 specimens were manufactured with direct laser deposition to analyze the isothermal hardening response of Alloy K-500. The laser deposited and wrought materials were precipitation hardened at three different temperatures (600 °C, 650 °C, and 700 °C) and various times. A relationship between the hardness and the volume fraction of Ni3(Ti,Al) was developed, and the subsequent analysis showed that the corresponding Johnson-Mehl-Avrami time constants (or n-values) ranged from 1.1 to 1.3 at an aging temperature 600 °C, and decreased to values ranging from 0.6 to 0.66 at an aging temperature of 700 °C. For site saturation and spherical precipitates, the expected n-value is 1.5. This analysis showed that the mechanism for precipitation changed as a function of temperature. The results of the analysis at higher temperatures were rationalized by the possibility of the decay of quenched-in vacancies, precipitation along the grain boundaries, and precipitation along the dislocations. It was, however, difficult to confirm these possibilities with transmission electron microscopy (TEM), since imaging the precipites is difficult at very early aging times. Finally, it was determined that the heat treatment schedule of laser welded or laser clad Alloy K-500 should be similar to that of wrought Alloy K-500.

A series of annulus welds were made between 304 and 304L stainless steel coaxial tubes using both pulsed laser beam welding (LBW) and pulsed gas tungsten arc welding (GTAW). In this application, a change in process from pulsed LBW to pulsed gas tungsten arc welding was proposed to limit the possibility of weld solidification cracking since weldability diagrams developed for GTAW display a greater range of compositions that are not crack susceptible relative to those developed for pulsed LBW. Contrary to the predictions of the GTAW weldability diagram, cracking was found.This result was rationalized in terms of the more rapid solidification rate of the pulsed gas tungsten arc welds. In addition, for the pulsed LBW conditions, the material compositions were predicted to be, by themselves, “weldable” according to the pulsed LBW weldability diagram. However, the composition range along the tie line connecting the two compositions passed through the crack susceptible range. Microstructurally, the primary solidification mode (PSM) of the material processed with higher power LBW was determined to be austenite (A), while solidification mode of the materials processed with lower power LBW apparently exhibited a dual PSM of both austenite (A) and ferrite-austenite (FA) within the same weld. The materials processed by pulsed GTAW showed mostly primary austenite solidification, with some regions of either primary austenite-second phase ferrite (AF) solidification or primary ferrite-second phase austenite (FA) solidification. This work demonstrates that variations in crack susceptibility may be realized when welding different heats of “weldable” materials together, and that slight variations in processing can also contribute to crack susceptibility.