Use of tapered specimens in studies on growth of single crystals of gadolinium

JOURNAL OF THE LESS-COMMONMETALS

352

Short

Communications

Use of tapered specimens in studies on growth of single crystals of gadolinium* Tapered

tensile specimens

were made starting

with vacuum

distilled

gadoli-

nium metal of 99.9% purity obtained from Dr. A. H. DAANE’S group at the Ames Laboratory. One specimen was encapsulated in a f in. diam. tantalum tube with ends arc-welded in an atmosphere of 300 mm of Hg helium. This capsule was then sealed in an evacuated 22 mm I. D. quartz capsule. Both capsules were required as the tantalum protects the gadolinium from reaction with quartz and the quartz protects the tantalum during the annealing periods, After annealing for 4 h at 1150°C, the specimen was removed from the capsules and strained in tension. Gage marks every tin. along the 2 in. gage length indicated a distribution of strain from I to 8%. The specimen was sealed in tantalum and quartz, as before, and reannealed at 12oo’C for three days. Although the grains were visible due to evaporation from the grain boundaries, the specimen was split longitudinally with a spark cutter and etched with a 2% nitol solution. As can be seen in Fig. I, the largest grains appeared in the I to 2% strain area. Cylindrical samples (without taper) were annealed, strained and reannealed as previously

described.

Figure

2 is a photograph

of a sample annealed

at 115o’c

for

4 h, strained 1.3”/~ at a rate of 0.02 in./min, and reannealed at 12oo’C for three days. The initial grain size was approximately 800 grains per sq. in. One of the grains in

Fig. I. Tapered tensile specimen which has been sectioned longitudinally showing critical strain. * Contribution No. 1647. Work was performed in the Ames Laboratory of the U. S. Atomic Energy Commission. J.

.~%'-CO?WVZO~

Metals,

8 (1965) 852-353

SHORT COMMUNICATIONS

Fig. 2. Gadolinium

353

tensile specimens after final anneal at ~zoo”C.

the sample shown in Fig. 2 was I in. long. Laue X-ray

photographs

showed that the

grain was relatively strain free. Photographs taken after rotating the crystal 180” displayed an inverted mirror image confirming that the single crystal extended through the cross section. One sample that had been strained about 1.0% also had a single grain about in. long. Another sample strained 0.66’7, failed to recrystallize. This was apparently below the minimum strain needed to produce recrystallization at 1200°C. Because of I

a limited amount of metal available, no cylindrical samples were run that had been strained more than 2%. It is concluded that the technique of using tapered specimens, originated by CHAPPELL~ in 1914 and recommended by others29334, can be used in optimizing growth conditions technique.

for producing

single crystals

of gadolinium

by the strain-anneal

I. M. PETERSON M. SMUTZ

Institute for Atomic Research and Department of Chemical Engineering, Iowa State University,

E. H. OLSON

Ames, Iowa (U.S.A.) I C. CHAPPELL,

J. Iron Steel Inst.,

I (1914)

2 R. KARNOP AND G. SACHS, 2. Phys., 52 3 E. S. FISHER, USAEC Rept. ANL-g160 4 K. W. K. HONEYCOMBE,

Received

February

Met. Rev.,

460. (1928)

301.

(1954). 4 (1959) I.

znd, 1965 J.

ihS-Common

Metals,

8 (1965) 352-353