The influence of precipitation of alpha2 on properties and microstructure in TIMETAL 6-4

Zhiwei Wu, Chunlei Qiu, V. Venkatesh, Hamish L. Fraser, R. E. A. Williams, G. B. Viswanathan, Matthew Thomas, S. Nag, Rajarshi Banerjee, Michael H. Loretto

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Abstract

Samples of Hot Isostatically Pressed (HIPped) powder of TIMETAL 6-4 (Ti-6Al-4V, compositions in wt pct unless indicated), which was HIPped at 1203 K (930 C), and of forged bar stock, which was slowly cooled from above the beta transus, were both subsequently held at 773 K (500 C) for times up to 5 weeks and analyzed using scanning and transmission electron microscopy and atom probe analysis. It has been shown that in the samples aged for 5 weeks at 773 K (500 C), there is a high density of alpha2 (α2, an ordered phase based on the composition Ti3Al) precipitates, which are typically 5 nm in size, and a significantly smaller density was present in the slowly cooled samples. The fatigue and tensile properties of samples aged for 5 weeks at 773 K (500 C) have been compared with those of the HIPped powder and of the forged samples which were slowly cooled from just above the transus, and although no significant difference was found between the fatigue properties, the tensile strength of the aged samples was 5 pct higher than that of the as-HIPped and slowly cooled forged samples. The ductility of the forged samples did not decrease after aging at 773 K (500 C) despite the strength increase. Transmission electron microscopy has been used to assess the nature of dislocations generated during tensile and fatigue deformation and it has been found that not just is planar slip observed, but dislocation pairs are not uncommon in samples aged at 773 K (500 C) and some are seen in slowly cooled Ti6Al4V.

Original languageEnglish
Pages (from-to)1706-1713
Number of pages8
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume44
Issue number4
DOIs
Publication statusPublished - Apr 2013
Externally publishedYes

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