Aging response of coarse- and fine-grained β titanium alloys

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 405; no. 1; pp. 296 - 305
• Main Authors: Ivasishin, O.M., Markovsky, P.E., Semiatin, S.L., Ward, C.H.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 25-09-2005; Elsevier
• Subjects: Aging; Beta titanium alloys; Continuous heat treatment; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Physics; Solid solution, precipitation, and dispersion hardening; aging; Treatment of materials and its effects on microstructure and properties; Aging; Continuous heat treatment; Beta titanium alloys; Grain size; Electrical conductivity; Ductility; XRD; Heat treatments; Titanium base alloys; Titanium alloys; Optical microscopy; Precipitation; Transmission electron microscopy; Scanning transmission electron microscopy; Microstructure; Aging: Continuous heat treatment
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2005.06.027

The effect of heating rate to aging temperature and β grain size on the aging behavior of three metastable β titanium alloys, TIMETAL-LCB, VT22 and Ti-15-3-3-3 (‘Ti-15-3’), was established using in situ resistivity measurements, X-ray diffraction, optical microscopy, SEM, TEM and STEM characterization. The results revealed the alloys could be divided into two classes based on their aging behavior. TIMETAL-LCB and VT-22 formed fine plate-like α at slow heating rates to the aging temperature. This behavior was determined to be due to the precipitation of isothermal ω at low temperatures, which serves as nucleation sites for α. The slow heating rate yielded the best balance of strength and ductility, particularly in alloys with a fine (∼10
μm) β grain size. At high heating rates, the formation of isothermal ω was avoided, leading to coarse, plate-like α microstructures with less desirable properties. Ti-15-3, on the other hand, exhibited β phase separation during isothermal aging rather than isothermal ω formation. Much slower cooling rates were required to form fine α laths in Ti-15-3 compared to the other two alloys. The importance of specifying heating rate and aging temperature for the industrial heat treatment of β titanium alloys was thus established.