Abstract
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/mm2 and 1.0 J/mm2) 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, Af) which predominantly consisted of an equiaxed grain structure, as compared to the middle (1.5–5.7% Af) and the bottom regions (2.6–4.5% Af), 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.
Highlights
Directed Energy Deposition (DED) is an additive manufacturing (AM) process utilized for varied applications such as rapid prototyping, cladding, building components and part features, in-situ alloying, repair and refurbishing applications [1,2,3]
All the parameter sets considered in this experimental design yielded sound and continuous deposition of material
The height of the deposits decreased with microstructure and texture in DED single track specimens
Summary
Directed Energy Deposition (DED) is an additive manufacturing (AM) process utilized for varied applications such as rapid prototyping, cladding, building components and part features, in-situ alloying, repair and refurbishing applications [1,2,3]. The process offers advantages such as: (a) the capability to achieve high deposition volumes in a large build envelope [4]; (b) the ability to deposit compositionally and/or functionally graded materials [5,6,7]; (c) ability to deposit materials on top of flat and curved substrate surface; and (d) adaptability to existing CNCs and robotic systems, which provides an edge over metal powder-bed fusion (PBF) processes. High deposition rate -directed energy deposition (HDR-DED) process is of specific interest in this work as it can have direct implications on processing times and economics. Most of the work conducted far has involved feed rates lower than 0.5 kg/h, Metals 2020, 10, 96; doi:10.3390/met10010096 www.mdpi.com/journal/metals
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