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Metallurgical Transactions A

, Volume 6, Issue 11, pp 2103–2114 | Cite as

The precipitation of α-phase in metastable β -phase Ti alloys

  • Cecil G. Rhodes
  • James C. Williams
Transformations

Abstract

The isothermal decomposition of metastable β-phase in Ti-14 wt pct Mo-6 wt pct Al and Ti-11.6 wt pct Mo alloys has been studied by electron microscopy. Two distinct types of α-phase are observed as decomposition products. Type 1 α obeys the well-known Burgers orientation with respect to the β-phase matrix. Type 2 α, which is characterized by arced reflections in the electron diffraction patterns, does not obey the Burgers orientation relation, but rather can be described as being in a {10–12} 〈10–11〉 twin orientation with respect to Burgers orientation α. The Type 1 α forms initially at aging temperatures in the range of 400°C to 650°C, and is replaced ty Type 2 α after longer holding times at the aging temperature. The Type 1 α precipitates form as monolithic plates in the ternary alloy and as monolithic needles in the binary. The Type 2 precipitates in the ternary alloy occur as very fine, contiguous particles in a colony-like arrangement wherein the colony has a plate morphology. The Type 2 precipitates in the binary alloy form as a peripheral shell around the Type 1 needle. Two possible mechanisms describing the formation of Type 2 α from Type 1 α are considered. The first of these is mechanical twinning of Type 1 α plates, and the second is a nucleation and growth mechanism which is driven by a composition difference between Types 1 and 2. The former is concluded to be less likelv than the latter.

Keywords

Metallurgical Transaction Electron Diffraction Pattern Ternary Alloy Habit Plane Zone Pattern 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© The Minerals, Metals & Materials Society - ASM International - The Materials Information Society 1975

Authors and Affiliations

  • Cecil G. Rhodes
    • 1
  • James C. Williams
    • 2
  1. 1.Science CenterRockwell InternationalThousand Oaks
  2. 2.Dept. of Metallurgy and Materials ScienceCarnegie-Mellon UniversityPittsburgh

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