Journal
MATERIALS & DESIGN
Volume 90, Issue -, Pages 551-561Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.matdes.2015.10.141
Keywords
Additive manufacturing; Titanium alloy; Fatigue crack propagation; Residual stress; Microstructure
Categories
Funding
- China Scholarship Council [201406025015, 2012094300044]
- Aviation Industry Corporation of China [2012-5023]
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Fatigue crack propagation tests of Ti-6Al-4V fabricated by the Wire+Arc Additive Manufacturing (WAAM) process are analysed. Crack growth rate and trajectory are examined before and after the crack tip crossing an interface between the WAAM and wrought alloys. The study has focused on the microstructure and residual stress effect. First, the differences in crack growth rate and path between WAAM and wrought alloys are attributed to their different microstructure; the equiaxed wrought alloy has straight crack path, whereas the WAAM lamellar structure causes tortuous crack path resulting in lower crack growth rate. Second, based on measured residual stress profile in the as-built WAAM piece, retained residual stress in the much smaller compact tension specimens and its effect on crack growth rate are calculated by the finite element method. Numerical simulation shows considerable residual stress in the test specimen and the stress magnitude depends on the initial crack location and propagation direction in relation to the WAAM-wrought interface. Residual stress is released immediately if the initial crack is in the wrought substrate; hence it has little effect. In contrast, when crack grows from WAAM to wrought, residual stress is retained resulting in higher stress intensity factor; hence greater crack growth rate. (C) 2015 Elsevier Ltd. All rights reserved.
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