Grain structure control during metal 3D printing by high-intensity ultrasound

C J Todaro,D Zhang,M A Easton,D Qiu,M J Bermingham,M Brandt,M Qian,E W Lui,D H Stjohn

doi:10.1038/s41467-019-13874-z

C J Todaro, D Zhang + Show 7 more

Open Access

https://doi.org/10.1038/s41467-019-13874-z

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Journal: Nature Communications	Publication Date: Jan 9, 2020
Citations: 446	License type: open-access

Affiliation: RMIT University, University of Queensland

Abstract

Additive manufacturing (AM) of metals, also known as metal 3D printing, typically leads to the formation of columnar grain structures along the build direction in most as-built metals and alloys. These long columnar grains can cause property anisotropy, which is usually detrimental to component qualification or targeted applications. Here, without changing alloy chemistry, we demonstrate an AM solidification-control solution to printing metallic alloys with an equiaxed grain structure and improved mechanical properties. Using the titanium alloy Ti-6Al-4V as a model alloy, we employ high-intensity ultrasound to achieve full transition from columnar grains to fine (~100 µm) equiaxed grains in AM Ti-6Al-4V samples by laser powder deposition. This results in a 12% improvement in both the yield stress and tensile strength compared with the conventional AM columnar Ti-6Al-4V. We further demonstrate the generality of our technique by achieving similar grain structure control results in the nickel-based superalloy Inconel 625, and expect that this method may be applicable to other metallic materials that exhibit columnar grain structures during AM.

Highlights

Additive manufacturing (AM) of metals, known as metal 3D printing, typically leads to the formation of columnar grain structures along the build direction in most as-built metals and alloys
Fusion-based metal additive manufacturing (AM) processes are featured by small melt pools and steep temperature gradients from the solid–liquid interface toward the liquid metal
We further demonstrate that the proposed approach applies to AM of nickel-based superalloy Inconel 625, which shows strong columnar grains as well by fusion-based AM43–45, and anticipate that it can apply to the AM of other metallic materials

Summary

Introduction

Additive manufacturing (AM) of metals, known as metal 3D printing, typically leads to the formation of columnar grain structures along the build direction in most as-built metals and alloys. The solidification process shows a strong epitaxial growth tendency from layer to layer while the number of nucleation events is limited due to both the absence of potent nucleant particles and the small melt pool volume (consumed quickly by epitaxial growth) This leads to columnar grains along the build direction in most additively manufactured metallic materials, which cause property anisotropy, reduce mechanical performance and increase tendency toward hot tearing. The combination of nucleant particles with process control can enlarge the equiaxed region on the G–V plot This has proved effective for AM of Al-based metals via the addition of Al3(Sc, Zr)[27], TiB2 Successful suppression of the columnar grain structures during AM by ultrasound has not been reported to date

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Conclusion