Phase transition in an Fe-23.2Al-4.1Ni alloy
- PDF / 2,986,055 Bytes
- 7 Pages / 613 x 788.28 pts Page_size
- 112 Downloads / 169 Views
I.
INTRODUCTION
A L T H O U G H the effects of nickel addition on the microstructure of the Fe-A1 binary alloy have been extensively studied by many workers,[l-121 information conceming this addition on the B2 --> DO3 ordering transition of the Fe-A1 binary alloys is very deficient. We are aware of only three articles t13,~4,15]in which the effects of nickel addition on the B2 --~ D03 ordering transition were predicted. In 1972, S w a n n e t al. first reported that the addition o f nickel to the Fe-A1 binary alloys lowers the B2 --> D03 transition temperature and also expands the (A2 + B2) phase field. [13] It is further reported by Athanassiadis et al. in 1977 that the Fe-25 at. pct Al-xNi alloys are single phase of D03-type up to about 4.0 at. pct nickel addition. Above this content, the ordered D03 phase changes to ordered B2-type phase, t~41However, in contrast to the above predictions, Mendiratta and Lipsitt claimed that the addition of nickel raises the D 0 3 ~ B2 transition temperature, f~51 In order to clarify the discrepancy between them, a transmission electron microscopy study was performed to investigate the effect of 4.1 at. pct nickel addition on the ordering transition of an Fe-23.2 at. pct AI alloy. Based on our present study, it is found that the addition of 4.1 at. pct nickel to the Fe-23.2A1 alloy indeed lowered the B2 ~ D 0 3 transition temperature. In addition, two kinds of ordered B2 phase were always observed simultaneously in the present alloy after being solution heat-treated, quenched, and then aged at 725 ~ or below. It is worthwhile to note that the coexistence of two kinds of ordered B2 phase has not previously been observed by other workers in the Fe-A1-Ni ternary alloy system.
II.
EXPERIMENTAL PROCEDURE
The alloy, Fe-23.2 at. pct AI-4.1 at. pct Ni, was prepared in an air induction furnace by using electrolytic iron (99.5 pct), electrolytic aluminum (99.7 pct), and electrolytic nickel (99.9 pct). The melt was cast into a 20 x 30 x 100 mm steel mold. After being homogenized at 1200 ~ for 12 hours under a protective argon atmosphere, the ingot was sectioned into 2-mm-thick T.F. LIU, Professor, Institute of Materials Science and Engineering, and S.C. JENG and C.C. W U , Graduate Students, Institute of Mechanical Engineering, are with the National Chiao Tung University, Hsinchu, Taiwan 30043, Republic of China. Manuscript submitted June 10, 1991. METALLURGICAL TRANSACTIONS A
slices. These slices were subsequently solution heat-treated at 1150 ~ for 2 hours and then rapidly quenched into room-temperature water. The aging processes were performed at temperatures ranging from 500 ~ to 1050 ~ for various times in a salt bath and then rapidly quenched into water. Electron microscopy specimens were prepared by means of a double-jet electropolisher with an ~ electrolyte of 75 pct acetic acid, 15 pct ethanol, and 10 pct perchloric acid. The polishing temperature was kept in the range from - 1 0 ~ to 10 ~ and the current densit2y was kept in the range from 3.0 x 104 to 4.0 x 104 A / m . Elec
Data Loading...
