THE FORMATION OF ORDERED OMEGA-RELATED PHASES IN ALLOYS OF COMPOSITION TI4AL3NB

被引:221
作者
BENDERSKY, LA [1 ]
BOETTINGER, WJ [1 ]
BURTON, BP [1 ]
BIANCANIELLO, FS [1 ]
SHOEMAKER, CB [1 ]
机构
[1] OREGON STATE UNIV, DEPT CHEM, CORVALLIS, OR 97331 USA
来源
ACTA METALLURGICA ET MATERIALIA | 1990年 / 38卷 / 06期
关键词
D O I
10.1016/0956-7151(90)90165-D
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
During cooling of an alloy of composition Ti4Al3Nb from a B2 phase field above 1100°C, a metastable trigonal (P3m1) ω-related phase, designated ω″, forms along with small amounts of D019 and L10 phases. The ω″ phase exhibits partial collapse of 111 planes and reordering relative to its B2 parent. An apparently equilibrium low temperature phase with the B82 structure was found after 26 days of annealing at 700°C. Both ω″ and B82 structures were verified by means of transmission electron microscopy and by single crystal X-ray diffraction. The latter permitted detailed analysis of the collapse parameters and site occupancies. The observed transformation path, B2(Pm3m)→ω″(P3m1)→B82 (P63/mmc), occurs in two steps. The first involveds a subgroup transition during cooling that is primarily displacive with reordering consistent with the trigonal symmetry imposed by the ω-collapse. The second involves a supergroup transition during prolonged annealing that is primarily replacive and constitutes a chemical disordering. The direct equilibrium transformation, B2→B82, without the formation of an intermediate trigonal phase, can only occur by a reconstructive transformation. © 1990.
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页码:931 / 943
页数:13
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