The fracture of ordered Zr3AI polycrystals
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I. INTRODUCTION BASED on the hypothesisz of order strengthening to reduce irradiation creep, a program is in progress to develop more creep resistant structural components for use in nuclear power reactors. The aim is to use an ordered phase as the matrix. The candidate material is Zr3A1 (L12 or Cu3Autype) and the program encompasses alloy preparation, componentfabrication, structure/property investigations and irradiation response. Of the many objectives, one is to understand the physical processes underlying the metallurgy of the material, and it was with this goal in mind that the present study was undertaken. Thus, the purpose of this paper is to describe the tensile fracture of Z r ~ l polycrystals. In so doing, the work extends our knowledge of the mechanical behavior of the alloy which, until now, has been more or less limited to studies of y i e l d i n g and w o r k - h a r d e n i n g . It a l s o c o n t r i b u t e s to knowledge of both the f r a c t u r e of i n t e r m e t a l l i c c o m pounds and the f r a c t u r e of d u c t i l e a l l o y s . Zr3A1 contains 8.97 wt pct A1 and f o r m s below 1265 K v i a the p e r i t e c t o i d t r a n s f o r m a t i o n e'3 Z r + Zr2A1 Zr3A1. It cannot be d i s o r d e r e d by quenching, 4 i m p l y ing that it r e m a i n s fully o r d e r e d to its t e m p e r a t u r e of d e c o m p o s i t i o n , and it p o s s e s s e s n e i t h e r g r o w n - i n antiphase boundaries (APB's) nor APB ribbons sepa-
r a t i n g s u p e r l a t t i c e p a r t i a l d i s l o c a t i o n s . 4 Instead, {111} i n t r i n s i c s t a c k i n g faults s e p a r a t e a/3 (211> s u p e r l a t t i c e 9 . . 4 p a r h a l d m l o c a h o n s , and slip o c c u r s by the m o v e m e n t of t h e s e p a r t i a l s .
2. EXPERIMENTAL The test specimens were the same ones described earlier in conjunction with the yielding and work hardening studies; ~ viz Zr-8.6 wt pct AI and Zr-8.9 wt pct A1 tensile specimens transformed to a Zr3AI matrix. The low aluminum alloy was prepared from reactor grade sponge zirconium and aluminum of 99.9 pct purity, and contained both ~Zr(AI) and Zr2AI. The high aluminum alloy was prepared from crystal bar zirconium and aluminum of >99.999 pct purity, and, when well-annealed, contained less ~Zr(AI) and less Zr2AI than the 8.6 pct A1 alloy. Table I summarizes the microstructures. T h e s p e c i m e n s w e r e d e f o r m e d at t e m p e r a t u r e s f r o m 77 to 1175 K and, u n l e s s o t h e r w i s e noted, at a t e n s i l e s t r a i n r a t e of 2.7 x 10 "~ s -1. T e s t i n g at e l e v a t e d t e m p e r a t u r e s was at r e d u c e d p r e s s u r e (~-4 x 10 "~ P a ) . T h e d e f o r m e d s p e c i m e n s w e r e e x a m i n e d by o p t i c a l m i -
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Table I. Microstructures of the Zr3AI-Based Alloys Used in This Investigation aZr(AI)
Alloy (Wt Pct AI)
Grain Size, d* (tam)
Vol Pct
8.6-+ 0.1 5 6-10 8.9-+0.05 1.6,3.5t 3-+2 8.3-60t ~0.1
Particle Diam (/am) 1-2 1-2 1-2
12
Zr 2 AI
Average Part
Data Loading...
