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

TLDR

Additive manufacturing of metals typically produces columnar grains along the build direction, causing property anisotropy that hinders component qualification and targeted applications. The study demonstrates, without altering alloy chemistry, a solidification‑control approach that yields equiaxed grain structures and enhanced mechanical properties in printed metallic alloys. By applying high‑intensity ultrasound during laser powder deposition of Ti‑6Al‑4V, the authors transform columnar grains into fine (~100 µm) equiaxed grains, and show the method also works on Inconel 625, suggesting broader applicability. This technique improves yield stress and tensile strength by 12 % over conventional AM Ti‑6Al‑4V and achieves comparable grain‑structure control in Inconel 625.

Abstract

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.