Dissolution of the Alpha Phase in Ti-6Al-4V During Isothermal and Continuous Heat Treatment
- PDF / 2,541,193 Bytes
- 15 Pages / 593.972 x 792 pts Page_size
- 16 Downloads / 210 Views
I.
INTRODUCTION
THE high-temperature dissolution of a second phase plays an important role in the processing of a number of metallic materials such as aluminum, nickel, and titanium-base alloys. In addition to solution treatment prior to the aging, dissolution can have a strong effect on the early stages of recrystallization and grain growth during exposure in a high-temperature, single-phase field.[1] For example, the rate and uniformity of dissolution can affect the uniformity of the annealed grain structure and the propensity for defects such as abnormally-large grains.[2,3] Such considerations play a crucial role in the
S.L. SEMIATIN, M. OBSTALECKI, E.J. PAYTON, A.L. PILCHAK, P.A. SHADE, and J.S. TILEY are with the Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, OH 45433. Contact e-mail: [email protected] N.C. LEVKULICH and J.M. SHANK are with UES, Inc., 4401 Dayton-Xenia Rd, Dayton, OH 45432. D.C. PAGAN is with the Cornell High Energy Synchrotron Source, Ithaca, NY 14853. F. ZHANG is with CompuTherm LLC, Middleton, WI 53562. Manuscript submitted November 29, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
design of conventional and rapid heat-treatment operations to produce creep-resistant, coarse-grain microstructures in nickel-base superalloys and fully-transformed (colony- or Widmanstatten-alpha) microstructures in titanium alloys.[4–7] The dissolution of a second phase can also be of importance with regard to plastic flow and microstructure evolution during hot deformation, as may occur during solid-state joining processes such as inertiaand linear-friction welding. In these instances, the dissolution of a second phase promotes gross plastic flow and dynamic recrystallization which are key to bringing atomically-clean metal surfaces into contact and producing sound metallurgical bonds.[8,9] Because of the transient nature of dissolution, especially in a high-temperature single-phase field, the measurement of dissolution kinetics can be very challenging. Common methods include furnace heat treatment/water quenching of samples with thin cross section (followed by metallography),[10–13] differential scanning calorimetry (DSC)/differential thermal analysis (DTA),[14,15] and direct resistance heating (incorporating concurrent resistivity measurements or followed by metallography).[6,16,17] For example, the detailed kinetics of dissolution of c¢ during supersolvus heat treatment of nickel-base superalloys has been shown to require times
of the order of 1 to 4 minutes using both furnace and direct-resistance methods.[12,17] There is also a number of reports of the time required for the dissolution of various strengthening phases in aluminum alloys under both isothermal (constant temperature) and continuous-heating conditions.[10,14,15] Surprisingly, there is only limited information on alpha-dissolution in two-phase (alpha/beta) titanium alloys.[18–21] These efforts describe subtransus behavior or the broad aspects of dissolution during continuous h
Data Loading...
