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

oleh: Suhas Sreekanth, Ehsan Ghassemali, Kjell Hurtig, Shrikant Joshi, Joel Andersson

Format: Article
Diterbitkan: MDPI AG 2020-01-01

Deskripsi

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<sup>2</sup> and 1.0 J/mm<sup>2</sup>) 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&#8722;9.6% area fraction, A<sub>f</sub>) which predominantly consisted of an equiaxed grain structure, as compared to the middle (1.5&#8722;5.7% A<sub>f</sub>) and the bottom regions (2.6&#8722;4.5% A<sub>f</sub>), 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 &lt;100&gt; crystallographic direction was observed to be the preferred growth direction of columnar grains while equiaxed grains had a random orientation.