Microstructural study of the titanium alloy Ti-15Mo-2. 7Nb-3Al-0. 2Si (TIMETAL 21S)
- Univ. of Wisconsin, Madison, WI (United States). Dept. of Materials Science and Engineering
A relatively new titanium alloy, TIMETAL 21S (Ti-15Mo-2.7Nb-3Al-0.2Si-0.15O (in wt pct)), is a potential matrix material for advanced titanium matrix composites for elevated temperature use. In order to develop a perspective on the microstructural stability of this alloy, the influence of several commonly used heat treatments on the microstructure of TIMETAL 21S was studied using optical and transmission electron microscopy (TEM). Depending on the specific thermal treatment, a number of phases, including [alpha], [omega]-type, and silicide, can form in this alloy. It was found that both recrystallized and nonrecrystallized areas could be present in the microstructure of an annealed bulk alloy, but the microstructure of annealed sheet alloy was fully recrystallized. The mixed structure of the bulk alloy, developed as a result of inhomogeneous deformation, could not be removed by heat treatment alone at 900 C. Athermal [omega]-type phase formed in this alloy upon quenching from the solution treatment temperature (900 C). Silicide precipitates were also found in the quenched sample. Thermal analysis was used to determine the [beta] transus and silicide solvus as close to 815 C and 1,025 C, respectively. In solution-treated and quenched samples, a high-temperature aging at 600 C resulted in the precipitation of [alpha] phase. The precipitation reaction was slower in the recrystallized regions compared to the nonrecrystallized regions. During low-temperature aging (350 C), the ellipsoidal [omega]-type phase persisted in the recrystallized areas even after 100 hours, whereas a high density of a precipitates developed in the nonrecrystallized areas within only 3 hours. The observed behavior in precipitation may be related to the influence of substructure in the nonrecrystallized areas, providing for an enhanced kinetics during aging.
- OSTI ID:
- 7087050
- Journal Information:
- Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States), Vol. 25:6; ISSN 0360-2133
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALUMINIUM ALLOYS
MICROSTRUCTURE
MOLYBDENUM ALLOYS
NIOBIUM ALLOYS
TITANIUM BASE ALLOYS
CRYSTAL-PHASE TRANSFORMATIONS
EXPERIMENTAL DATA
MATRIX MATERIALS
OXYGEN ADDITIONS
SILICON ADDITIONS
ALLOYS
DATA
INFORMATION
MATERIALS
NUMERICAL DATA
PHASE TRANSFORMATIONS
SILICON ALLOYS
TITANIUM ALLOYS
360102* - Metals & Alloys- Structure & Phase Studies