Browsing by Author "Griffiths, R. Joey"
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- Additive Friction Stir-Enabled Solid-State Additive Manufacturing for the Repair of 7075 Aluminum AlloyGriffiths, R. Joey; Petersen, Dylan T.; Garcia, David; Yu, Hang Z. (MDPI, 2019-08-23)The repair of high strength, high performance 7075 aluminum alloy is essential for a broad range of aerospace and defense applications. However, it is challenging to implement it using traditional fusion welding-based approaches, owing to hot cracking and void formation during solidification. Here, the use of an emerging solid-state additive manufacturing technology, additive friction stir deposition, is explored for the repair of volume damages such as through -holes and grooves in 7075 aluminum alloy. Three repair experiments have been conducted: double through-hole filling, single through-hole filling, and long, wide-groove filling. In all experiments, additive friction stir deposition proves to be effective at filling the entire volume. Additionally, sufficient mixing between the deposited material and the side wall of the feature is always observed in the upper portions of the repair. Poor mixing and inadequate repair quality have been observed in deeper portions of the filling in some scenarios. Based on these observations, the advantages and disadvantages of using additive friction stir deposition for repairing volume damages are discussed. High quality and highly flexible repairs are expected with systematic optimization work on process control and repair strategy development in the future.
- Towards underwater additive manufacturing via additive friction stir depositionGriffiths, R. Joey; Gotawala, Nikhil; Hahn, Greg D.; Garcia, David; Yu, Hang Z. (Elsevier, 2022-11)Given the challenges in feed material supply and quality control, metal additive manufacturing has rarely been implemented in austere environments, especially underwater. This paper explores the underwater operation potential of an emerging solid-state additive technology: additive friction stir deposition, wherein material feeding and bonding are enabled by mechanical forces with minimal influences from water. It is demonstrated that additive friction stir deposition of 304 stainless steel can be successfully performed with the print head and substrate immersed in water. High temperature is reached in the deposition zone (>60% melting temperature); the material deposition behavior is similar to that in typical open-air operation. The as-deposited material is fully-dense, having fewer annealing twins and a substantially smaller grain size than the feed material (4.98 lm vs. 31.44 lm). Such microstructural changes stem from dynamic recrystallization caused by the large strain and high temperature introduced during deposition. In addition to grain refinement, small equiaxed dispersoids (-2-3 lm or less) are formed and evenly distributed in the austenite steel matrix. Rich in Cr, Mn, and O, these particles likely result from the reaction between the elements in stainless steel and water at elevated temperatures. (c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).