Abstract
Tensile testing and cyclic tensile loading measurements were performed on heat-treated samples of annealed Ti-2448 and cold-rolled Ti-2448. Quenching from above the β-transus produces an alloy that is highly superelastic has ultra-low elastic modulus (10-25. GPa) and exhibits hysteresis on loading-unloading cycles. On repeated cycling the strain energy absorbed in each cycle decreases. Annealed Ti-2448 exhibits a stable hysteresis loop. Peaks from the α″ phase are observed in X-ray diffraction (XRD) patterns, thus the material is quite lean in β-stabilising additions. The alloy is shown to be highly unstable when heat-treated. A combination of small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and X-ray diffraction (XRD) was employed to relate the thermally induced microstructural evolution to the change in mechanical properties. A heat-treatment of 80. °C to the cold-rolled material precipitated the ω phase causing embrittlement. Increasing the ageing temperature from 80 to 300. °C increased the stiffness, made the elastic regime more linear, and further embrittled the alloy. The low temperature heat-treatments precipitate both ω and α″ phases. A higher temperature ageing treatment at 450. °C increased the yield strength to over 1. GPa and caused embrittlement, indicating co-precipitation of α and ω phases.
| Original language | English |
|---|---|
| Pages (from-to) | 399-407 |
| Number of pages | 9 |
| Journal | Materials Science and Engineering A |
| Volume | 655 |
| Early online date | 22 Dec 2015 |
| DOIs | |
| Publication status | Published - 8 Feb 2016 |
Funding
J.C. and M.O. would like to acknowledge funding provided from the Japanese Society for the Promotion of Science (JSPS) . V.A.V. and J.C. would like to acknowledge support from the EPSRC doctoral prize fellowship and Marie Curie fellowship respectively. Funding was also provided by EPSRC under Grant EP/H0004882/0 . This work made use of the J.B. Cohen X-ray Diffraction Facility at the Materials Research Center of Northwestern University supported by the National Science Foundation MRSEC program ( DMR-1121262 ). The authors would like to thank Rui Yang for sample preparation, Shigeharu Ukai for the use of the Advanced High Temperature Laboratory at Hokkaido University, and the Imperial College London technical staff: Gary Stakalls, Russell Stracey, Simon Logsdail, Mike Lennon and Ben Wood for their continuous assistance.
Keywords
- aging
- electron microscopy
- mechanical characterisation
- phase transformation
- titanium alloys
- x-ray diffraction