Influence of Laser Powder Bed Fusion Process Parameters on Voids, Cracks, and Microhardness of Nickel-Based Superalloy Alloy 247LC.

Olutayo Adegoke,Joel Andersson,Håkan Brodin,Robert Pederson

doi:10.3390/ma13173770

Abstract

The manufacturing of parts from nickel-based superalloy Alloy 247LC by laser powder bed fusion (L-PBF) is challenging, primarily owing to the alloy’s susceptibility to cracks. Apart from the cracks, voids created during the L-PBF process should also be minimized to produce dense parts. In this study, samples of Alloy 247LC were manufactured by L-PBF, several of which could be produced with voids and crack density close to zero. A statistical design of experiments was used to evaluate the influence of the process parameters, namely laser power, scanning speed, and hatch distance (inherent to the volumetric energy density) on void formation, crack density, and microhardness of the samples. The window of process parameters, in which minimum voids and/or cracks were present, was predicted. It was shown that the void content increased steeply at a volumetric energy density threshold below 81 . The crack density, on the other hand, increased steeply at a volumetric energy density threshold above 163 . The microhardness displayed a relatively low value in three samples which displayed the lowest volumetric energy density and highest void content. It was also observed that two samples, which displayed the highest volumetric energy density and crack density, demonstrated a relatively high microhardness; which could be a vital evidence in future investigations to determine the fundamental mechanism of cracking. The laser power was concluded to be the strongest and statistically most significant process parameter that influenced void formation and microhardness. The interaction of laser power and hatch distance was the strongest and most significant factor that influenced the crack density.

Highlights

Laser powder bed fusion (L-PBF) is an additive manufacturing (AM) process, in which a laser is utilized to melt a powder on a powder bed or substrate one layer at a time
The process is conducted in an inert gas atmosphere and the geometry of the part is fed from a 3D computer-aided design (CAD) file
This was reflected in the calculated repeatability value of 0.91. This indicates that the location of the cubes may not be influencing the void content result. This is vital to the study as it shows that the voids are linked to the process parameters alone and were independent of the location on the build plate

Summary

Introduction

Laser powder bed fusion (L-PBF) is an additive manufacturing (AM) process, in which a laser is utilized to melt a powder on a powder bed or substrate one layer at a time. L-PBF gained attention in the manufacturing of gas turbine blades, for which Alloy 247LC (LC stands for low carbon) is a suitable material. This is a precipitation strengthened nickel-based superalloy that has good creep strength, high temperature oxidation, and good corrosion properties [1]. These blades have internal cooling channels with complex designs which are difficult to manufacture using conventional processes; they could be manufactured with the L-PBF process.

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