Decomposition of rapidly solidified Cu-Ti solid solutions
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estimate is based on the experimental observations and theoretical modeling of cooling rates by Ruhl '2 for the case of splat quenching. The parameters that Ruhl found to be of greatest importance in determining the cooling rate were the splat thickness and the interface heat transfer coefficient. Samples of a metastable Cu85Ti,5 ribbon were subjected to the following heat treatments: 300 ~ minutes and 398 ~ minutes. In each case, pieces of the asquenched ribbon were evacuated in pyrex ampules backfilled with 0.5 atm of helium. The temperature of the furnace was regulated to within plus or minus 1 ~ After heat treatment the ampules were quenched in an ice brine solution supercooled to a temperature of - 1 0 ~ thus causing the pyrex ampules to crack, and ensuring a rapid quench. The as-quenched ribbons were characterized initially using X-ray diffraction. A Rigaku X-ray diffractometer with a CuKa source was used. Both the heat treated and the asquenched ribbons were characterized using a JEOL 100 CX Transmission Electron Microscope (TEM). A dual gun Gatan Ion Miller Model 6000 was used to thin the ribbons for TEM observation using a gun current of 1 mA and a gun voltage of 6 kV. The results of Laughlin and Cahn z'3 are summarized in Figure 1. This schematic shows that an as-quenched Cu95Ti5 alloy has SRO (the {1 89 reflections), spinodal decomposition (satellites), and LRO (D I a reflections). With aging, the {1890} reflections decreased in intensity and the intensity of the Dla reflections increased. An electron diffraction pattern of a Cu85Ti,5 alloy that has been rapidly quenched from the liquid is shown in Figure 2. The existence of {1 89 SRO reflections is evident, but the LRO, D1, reflections are absent. At the same time oxide reflections can be seen near some fundamental reflections. Diffraction patterns were also obtained with a highly defocused condenser lens, and no satellites were observable. Thus, the as-quenched state of the Cu85Ti,5 alloy involves only the SRO. When the as-quenched alloys were heat treated at the temperatures and times given in the experimental procedure 9
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0+0 C.G. WOYCHIK is Senior Associate Engineer, Systems Technology Division, IBM Corporation, 1701 North Street, Endicott, NY 13760. R.J. RIOJA is Senior Engineer, Alcoa Technical Center, Alcoa Center, PA 15069. T. B. MASSALSKI and D. E. LAUGHLIN are Professors, Department of Metallurgical Engineering and Materials Science, CarnegieMellon University, Pittsburgh, PA 15213. Manuscript submitted January 16, 1985.
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F i g l - - S c h e m a t i c of a [00~] diffraction pattern of an as-quenched Cu95Ti5 alloy. The satellites represent long wavelength modulations, the crosses represent SRO, and the dots represent two variants of the LRO phase. VOLUME 16A, JULY 1985-- 1353
5. T. Hakkarainen: Doctor of Technology Thesis, Helsinki University of Technology, Ont
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