Effect of Direct Energy Deposition Process Parameters on Single-Track Deposits of Alloy 718

The effect of three important process parameters, namely laser power, scanning speed and laser stand-off distance on the deposit geometry, microstructure and segregation characteristics in direct energy deposited alloy 718 specimens has been studied. Laser power and laser stand-off distance were found to notably affect the width and depth of the deposit, while the scanning speed influenced the deposit height. An increase in specific energy conditions (between 0.5 J/mm(2) and 1.0 J/mm(2)) increased the total area of deposit yielding varied grain morphologies and precipitation behaviors which were comprehensively analyzed. A deposit comprising three distinct zones, namely the top, middle and bottom regions, categorized based on the distinct microstructural features formed on account of variation in local solidification conditions. Nb-rich eutectics preferentially segregated in the top region of the deposit (5.4-9.6% area fraction, A(f)) which predominantly consisted of an equiaxed grain structure, as compared to the middle (1.5-5.7% A(f)) and the bottom regions (2.6-4.5% A(f)), where columnar dendritic morphology was observed. High scan speed was more effective in reducing the area fraction of Nb-rich phases in the top and middle regions of the deposit. The < 100 > crystallographic direction was observed to be the preferred growth direction of columnar grains while equiaxed grains had a random orientation.