Titanium (Ti) alloys have been commonly used in the aerospace industry, not
only because they have a high strength-to-weight ratio (comparing to the steels)
but also their satisfactory corrosion resistance. Furthermore, they can be
assembled with the carbon fibre composite parts. However, conventional
manufacturing methods cause high material scrap rate and require lots of
machining to obtain the final shape and size, which increases both the
manufacturing time and cost. In order to improve the efficiency and reduce the
cost of Ti parts, Additive Manufacturing (AM) has been developed.
Rolled Wire and Arc Additive Manufacturing (rolled WAAM) is one of the AM
processes. The main characteristics of this technology is the reduced β grain
size to refine the alloy's microstructure. Both the ultimate tensile strength and
yield strength of Ti alloy made by rolled WAAM are at least 10% higher than
traditional wrought Ti.
This project is to investigate the fatigue crack growth rates of the Ti-6Al-4V built
by rolled WAAM process in both the longitudinal and transverse orientations to
study the effect of rolling on fatigue crack growth rate of WAAM processed Ti.
The project was carried out by testing the fatigue crack growth rates for 4
compact tension specimens. The test results of different orientations were
compared with each other, and scatters in fatigue life and fatigue crack growth
rate were found. Fatigue crack growth rate is lower in the longitudinal
specimens. The results are also compared with those of the unrolled WAAM
specimens tested in a previous project. It was found that rolling can significantly
improve the fatigue crack growth behaviour in WAAM processed Ti, and can
reduce the difference between the two orientations, i.e. achieving better
isotropic material properties. Recorded scatters may be caused by the process
induced residual stresses, error in measurement, and the test machine load
range being much higher than the applied loads. More specimens can be tested
to validate above observations further.
| Identifer | oai:union.ndltd.org:CRANFIELD1/oai:dspace.lib.cranfield.ac.uk:1826/8441 |
| Date | 11 1900 |
| Creators | Qiu, Xundong |
| Contributors | Zhang, Xiang |
| Publisher | Cranfield University |
| Source Sets | CRANFIELD1 |
| Language | English |
| Detected Language | English |
| Type | Thesis or dissertation, Masters, MSc by Research |
| Rights | © Cranfield University 2013. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright owner. |
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