Part I Nucleation kinetics of the β → αm transformation in Ti-ag and Ti-au alloys

Mechanisms of the massive transformation

“…Considerations based upon nucleation theory [8] requiring (McMaster University, Canada), Professor Vijay K. that ⌬F* Յ approximately 60 kT in order that nucleation Vasudevan (University of Cincinnati), and Dr. Eric A. Wilson may occur at a detectable rate [28] and comparisons of (Sheffield Hallam University, United Kingdom). Professor measured and calculated nucleation rates [115] support the William A. Soffa (University of Pittsburgh) is thanked for Figure 7 and Professor Soffa and Dr. John W. Cahn (NIST) view that the critical nucleus of a MT must be fully and many of the foregoing colleagues are thanked for spirited coherent (or nearly so) with respect to its matrix discussions about fundamental aspects of the MT. Professor phase.…”

“…Plichta et al [115] subsequently demonstrated immense discrepancies between measured nucleation rates of the (bcc) ␤ → (hcp) ␣ m transformation in Ti-Ag and Ti-Au alloys when critical nuclei were assumed to be entirely incoherent.…”

Massive-parent interphase boundaries and their implications on the mechanisms of the α → γ M massive transformation in Ti-Al alloys

“…The conventional TEM ( Figure 13) ⌬G* Ͻ 60 kT ). An experimental study of the crystallography and HRTEM results (Figure 14) also show that the ␥ M grain and morphology of the ␤ → m massive transformation in forms with a coherent interface with the ␣ grain against the Ag-Al system [14] showed that for 46 of 47 m crystals which it nucleates with the Burgers OR. analyzed, a Burgers OR was obtained exactly, or nearly so, Based on the reaction start temperatures and thermowith at least one of the parent ␤ grains forming the grain dynamic data of the ␣ → ␥ M massive transformation in a boundary at which nucleation occurred.…”

“…The random transfer of atoms across them. On the grounds of second issue, which was debated more extensively and is nucleation theory and calculated and experimental nucleation rates, Aaronson and associates [11][12][13][14][15] proposed that many of these boundaries are partially coherent during migrates through the agency of a ledge mechanism, [11][12][13][14][15][16] rather than involving random atom transfer across incoherent interfaces. Aspects related to this debate are the subject of this article and are discussed in more detail later, after the presentation of the results.…”

A Study of the Kinetics of Phase Transformations in Nb-Ti-Al Alloys

“…This is not to say, however, that all massive transformations do not occur this way [70,71]. Low index relationships between the massive and parent phases have been observed in numerous alloy systems, such as: Ag-Al, Ti-Al, Cu-Zn, Ag-Zn, Cu-Ga, Ag-Cd [42,43,[72][73][74][75]. A study of the nucleation rates for the ß to a m transformation in Ti-Ag and Ti-Au was performed through an incoherent nucleus model by Plichta et al [73], from which it was determined that the predicted rate of nucleation was thousands of orders of magnitude lower than that experimentally observed; this was taken as indication that the formation of massive nuclei with partially coherent interfaces had to occur in order for detectable levels of nucleation to be observed [42,73].…”