MICROSTRUCTURAL STUDY OF THE TITANIUM-ALLOY TI-15MO-2.7NB-3AL-0.2SI (TIMETAL-21S)

被引:36
作者
CHAUDHURI, K
PEREPEZKO, JH
机构
[1] Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, 53706, WI
来源
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE | 1994年 / 25卷 / 06期
关键词
D O I
10.1007/BF02652286
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
A relatively new titanium alloy, TIMETAL 21S (Ti-15Mo-2.7Nb-3Al-0.2Si-0.150 (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-degrees-C. Athermal omega-type phase formed in this alloy upon quenching from the solution treatment temperature (900-degrees-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-degrees-C and 1025-degrees-C, respectively. In solution-treated and quenched samples, a high-temperature aging at 600-degrees-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-degrees-C), the ellipsoidal omega-type phase persisted in the recrystaLlized areas even after 100 hours, whereas a high density of alpha 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. The alpha precipitates (formed during continuous cooling from the solution treatment temperature, low-temperature aging, and high-temperature aging) always obeyed the Burgers orientation relationship. With respect to the microstructure, TIMETAL 21S is similar to other solute-lean, metastable beta titanium alloys.
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页码:1109 / 1118
页数:10
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