The deformation mechanism for high-purity
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Corvallis, Oregon. This paper is based upon a thesis submitted by C. T. WANGin partial fulfillment of the requirements of the degree of Doctor of Philosophyat Oregon State University. Manuscript submitted September 20, 1971. METALLURGICAL TRANSACTIONS
lization was 30 g r a i n s / m m z. Others w e r e e l e c t r o n beam zone refined into single c r y s t a l s with e i t h e r or axial o r i e n t a t i o n s . This was c a r r i e d out at the Oak Ridge National L a b o r a t o r y with a s e e d ing technique at a vacuum of 10 -7 and 10 -1~ t o r r for two s u c c e s s i v e p a s s e s r e s p e c t i v e l y . It should be pointed out that r e p e a t e d e l e c t r o n beam melting or zone refining will not yield high-purity vanadium unl e s s the s t a r t i n g m a t e r i a l is low in i n t e r s t i t i a l s . 2'8 The f i r s t grade polycrystalUne m a t e r i a l was actually at the 99.98 pct level due to contamination during p r o c e s s i n g , while the m o n o c r y s t a l l i n e m a t e r i a l r e a c h e d the original 99.99 pct level apparently due to some purification in the final zoning under high vacuum conditions. The m o n o c r y s t a l l i n e rods were sawed into sections using a diamond impregnated copper a b r a s i v e cutting wheel. To p r e p a r e the gage section, an e l e c t r o p o l i s h i n g a p p a r a t u s was employed; the p r i n c i p l e for its c o n s t r u c tion was s i m i l a r to that of A v e r y , E b n e r , and Backofen. 16 The e l e c t r o l y t e used was 15 pct oxalic acid. To further i m p r o v e the surface finish of the single c r y s t a l s , they were then polished in a Buehler 1721-2 cell using 10 pct sulfuric acid as e l e c t r o l y t e . Back reflection Laue diffraction photographs were taken at the gage section in o r d e r to evaluate the perfection and orientation of the specimens. The second grade of vanadium in ingot form was f a b r i c a t e d into r o d s and machined into tensile s p e c i mens. After annealing, the grain size was about 100 g r a i n s / m m 2. Except for a few single c r y s t a l s for slip and twinning plane studies, all s p e c i m e n s were deformed using r a t e change and t e m p e r a t u r e change techniques. T e m p e r a t u r e s used for testing were as follows: 1) 77 K, boiling point of liquid nitrogen; 2) 113 K, freezing point of isopentane; 3) 160 K, freezing point of methyl alcohol; 4) 200 K, constant t e m p e r a t u r e liquid methyl alcohol cooled by liquid nitrogen; 5) 233 K, same method as for previous t e m p e r a t u r e ; and 6) 293 K, constant t e m perature water. F o r the t e m p e r a t u r e change e x p e r i m e n t s , 293 K was used as a r e f e r e n c e t e m p e r a t u r e . During the t e m p e r ature change the load was r e l a x e d to about 80 pct of VOLUME 3, DECEMBER 1972-3161
the higher t e m p e r a t u r e s t r e s s to minimize r e c o v e r y . The c r o s s h e a d velocity was maintained constant to produce a s t r a i n r a t e of a p p r o x i
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