Achieving ultra-high strength rapidly in Ti-3Al-8V-6Cr-4Mo-4Zr alloy processed by directed energy deposition

This work investigates the viability of fabricating Ti-3Al-8V-6Cr-4Mo-4Zr (Beta-C (TM)) using laser-based and powder-fed directed energy deposition. To determine an appropriate ageing strategy, heat treatments were conducted at 440 degrees C and 480 degrees C over different periods of time and their effectiveness were determined through hardness testing. After identifying an optimal ageing treatment, tensile properties were investigated on the samples in the as-built and aged conditions. The microstructure, hardness and tensile properties of the as-built sample was found to resemble that of a conventionallymanufactured and solution-treated alloy. However, as compared to conventionally-manufactured Ti3Al-8V-6Cr-4Mo-4Zr subjected to the same ageing temperature, the ageing process was much quicker with the DED-processed alloy because of its high dislocation density. Furthermore, the latter can also achieve much higher strength while also having comparable ductility. To achieve a similar ageing response and tensile behavior, conventionally-manufactured Ti-3Al-8V-6Cr-4Mo-4Zr would require cold-working prior to ageing. Carbon additions were also investigated to further accelerate the ageing response and to refine the beta grain size. While the ageing response was much quicker and a much harder alloy can be produced, the carbon amount added was insufficient for b grain refinement, which resulted in reduced ductility without a change in strength. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).