Comparison of laser deposition methods for the synthesis of AlxCoCrFeNi multi-principal element alloy

Abstract

Additive manufacturing (AM) of multi-principal element alloys (MPEAs) has enabled high throughput synthesis for rapid alloy design and development for targeted structural properties. However, the complex solidification cycles endured by the material during processing often yield disparate outcomes when porting the processing conditions between different laser deposition techniques. With difference in the cooling rates being a primary difference between laser metal deposition (LMD) and powder bed fusion (PBF), understanding the effects of the processing on the microstructures and material properties is critical to assess the printability of such complex alloys. Here, we compare the fabricability, quality, and structural properties of AlxCoCrFeNi MPEA synthesized by LMD and PBF. Our results indicate that the equiatomic MPEA processed using PBF exhibits interfacial cracks due to warping and bending between successive deposit layers, while the LMD produces crack free near-dense deposits. XRD characterization corroborates a relatively high lattice strain of 1.8 × 10−3 in the PBF sample resulting from the high residual stresses arising from the relatively high cooling rates (∼106 K/s) during the processing. While the PBF sample assumes smaller grains relative to the LMD processed alloy, no significant differences are noted in the crystallographic phases of the alloys produced by the two approaches. Also, the tool path employed to fabricate the alloy by LMD can facilitate gradation in the structural properties driven by the variation in thermal gradient during the synthesis. Further, we propose methods to map material space while porting processes within AM, enabling fabricability of alloys using PBF and DED.

Keywords

• Multi-principal element alloy
• Additive manufacturing
• Laser metal deposition
• Powder bed fusion
• Printability
• Lattice strain