The Influence of Precipitation of Alpha2 on Properties and Microstructure in TIMETAL 6-4

Abstract

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The formation of ordered clusters in Ti–7Al and Ti–6Al–4V

“…It is found that precipitation appears to occur much faster, and more strongly, in a-Ti which is alloyed, very slightly, with V in Ti-6Al-4V than in the pure binary Ti-Al. This is compared to results for Ti-Al-V [21], Ti-Al-Mo [26] and Ti-Al-Zr [27] alloys, where similar ternary alloying effects are observed.…”

“…Both Neeraj [19] and Brandes in Ti-7Al wt.% (12Al at.%) [5] observed diffuse spots in TEM, which could be sup-45 pressed by water quenching to provide a fully disordered a-Ti structure. More recently, ordering in the a phase of Ti-6Al-4V has been observed by Wu et al [21] at relatively short ageing times of 35 days at 500 C. In addition, Liew et al [17] studied Ti-9Al wt.% (15Al at.%) by field ion microscopy (FIM) after 500 hours ageing at 650 C and 750 C, where ordering could be observed in the TEM but compositional variations 50 could not. Therefore, the problem of quantifying this precipitation phenomenon has remained strongly intractable to analysis, by 1998-era atom probe tomography instruments (APT) [22,23,24,25], by TEM and by neutron diffraction.…”

“…The TEM studies in Ti-6Al-4V of Wu et al [21] found weak superlattice maxima in doubly exposed diffraction patterns taken from a sample slowly cooled from 930 C. However, it was not possible to obtain dark field images of precipitates from these re-the development of a 2 precipitates within the a phase was observed. It was reported that these precipitates possessed a composition of Ti 3 Al with a diameter between 5 and 10 nm.…”

“…It was reported that these precipitates possessed a composition of Ti 3 Al with a diameter between 5 and 10 nm. Wu et al [21] also presented APT studies illustrating Al-rich clusters corresponding to the Ti 3 Al phase observed in the electron diffraction patterns. In the centre 220 of the precipitates, the Al concentration was reported to be 20 at.% and the V concentration was approximately 2 at.%.…”

“…Al alloys [40,26,42,4,43,21,27,41] it is evident that ordering can occur in titanium alloys containing more then 6 wt.% Al along with Zr, Si, Mo, or V after shorter ageing times than in the binary Ti-Al alloys.…”