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

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.

Eleven-year follow-up of tooth replantation.

An 11-year clinical and radiographic follow-up of an avulsed tooth, replanted within 15 minutes, has been presented. The periodontal membrane can be traced around the replanted central incisor, indicating the tooth is not ankylosed and is functionally attached. It is not anchored immutably to the bone. The tooth has responded dynamically to growth and development of the maxilla and now abuts and aligns well with the other teeth in the arch.