The effects of Cr additions to binary TiAl-base alloys
- PDF / 2,684,942 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 54 Downloads / 217 Views
I.
INTRODUCTION
B E C A U S E of its attractive high-temperature properties, the lightweight compound T-TiA1 has received a great deal of research attention since early 1950. t~,2] Much of the attention was devoted to low-temperature deformability, since this is a major hindrance to actual uses. Early work of Marcinkowski e t al. ~3] and Greenberg I4,51 suggested that y aluminide deforms by slip of 1/21110] unit dislocations and [101] and 1/21112] superdislocations. The superdislocations would dissociate into a 1/61112] partial bounded by a {111} superlattice stacking fault. However, Shechtman et al. t61 and Hug et a l . [7"8] showed that in single-phase y materials, the 1/61112] partials tend to be pinned, forming sessile faulted dipoles. Recently, Huang and co-workers 19,t~ studied Al-lean binary alloys which contained a z-Ti3ml as a second phase. It was found that superdislocations are inactive in finegrained duplex alloys; instead, twinning on {111} planes, with the 1/61112] partial as the twin dislocation, becomes an important mode of deformation. This change in deformation mechanism is an indication of a reduced stacking fault energy. Correspondingly, duplex alloys are more ductile than single-phase alloys. However, the a2 phase, typically in the form of lamellar laths transformed from a, has the tendency to resist deformationJ l~ Also recently, alloying additions of Mn, V, or Cr were reported to enhance the plasticity of duplex alloys, as summarized in References 12 and 13. The effects of Mn and V additions have been characterized extensively. Hanamura e t a l . f14'15'161 concluded that Mn enhances plasticity by stabilizing thermal twins which providd nucleation sites for twin dislocations. Manganese was measured to lower stacking fault energy, u71 Huang and Hall t18j showed that V reduces the stability of transformed a : . Both Mn u9,2~ and V I~71were shown to substitute for A1 and, therefore, modify the Ti-A1 bond. t2tl All of the above three elements reduced the lattice unit cell volume. ~121 This study was aimed at understanding the effect of Cr additions to y-base alloys. Systematic variations in Cr and A1 concentrations were carried out, and their efSHYH-CHIN HUANG, Staff Metallurgist, and ERNEST L. HALL, Staff Scientist, are with GE Corporate Research and Development, Schenectady, NY 12301. Manuscript submitted April 29, 1991. METALLURGICAL TRANSACTIONS A
fects on ductility, microstructure, deformation, and lattice substitution were characterized. The results are compared to those obtained from parallel studies on binary ul] and TiA1-V alloys ~181in order to correctly assess the Cr effects. All of the materials studied here were processed v i a the rapid solidification route to ensure microstructural homogeneity.
II.
EXPERIMENTAL
Several y-base ternary alloys containing 45 to 54 at. pct A1 and 1 to 4 at. pct Cr were prepared by rapid solidification processing for this investigation. Each alloy was melt-spun into ribbon t221 which was then consolidated by cold compaction, hot isostatic pressing,
Data Loading...
