Structure-property relationships in thermomechanically treated beryllia dispersed nickel alloys
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is well known that the high t e m p e r a t u r e strength and s t a b i l i t y of a m e t a l can be g r e a t l y improved by a fine uniform d i s p e r s i o n of a stable r e f r a c t o r y oxide phase. These oxide d i s p e r s e d (OD) alloys can be f u r ther strengthened and s t a b i l i z e d by a p p r o p r i a t e t h e r m o m e c h a n i c a l t r e a t m e n t s . F o r example, TD-Ni in the a s - e x t r u d e d , fully dense condition has an 100 h r u p t u r e life of only about 3,000 p s i (2.1 k g / m m z) at 982~ (1255 K) but can be improved to 10,000 to 15,000 p s i (7.0 to 10.5 k g / m m z) by p r o p e r t h e r m o m e c h a n i c a l t r e a t m e n t s (TMT). While t h e r e a r e numerous examples of this type of i m p r o v e m e n t in p r o p e r t i e s brought about by controlled TMT of OD alloys in the l i t e r a t u r e , z-9 the m e c h a n i s m of this strengthening effect a p p e a r s to be inadequately known. T r a c e y and Worn, 1 F r a s e r , Meddings and Evans, 2 and F r a s e r and Evans s attributed the strengthening to an i m p r o v e d d i s t r i b u t i o n of the d i s p e r s e d phase and the development of a fibrous m i c r o s t r u c t u r e . Wilcox, Clauer and Hutchinson 4 and Wilcox and Clauer, 5 on the other hand, e m p h a s i z e the need for a l a r g e value of grain a s p e c t r a t i o (GAR). F r a s e r and Evans 3 have shown that equivalent s u b s t r u c t u r e s i z e and p r o p e r t i e s could be obtained with different volume f r a c t i o n s of ThO2 in nickel with different TMTs. R a s m u s s e n and Grant ~~ proposed a m e c h a n i s m for the strengthening p r o c e s s due to cold work, modified through i n t e r m e d i a t e anneals. They suggested that the apparent i n t e r p a r t i c l e spacing d e c r e a s e s with i n c r e a s ing cold work. The r o l e of the i n t e r m e d i a t e annealing step is to sweep many of the d i s l o c a t i o n s into low angle boundaries, p e r m i t t i n g f u r t h e r cold work with l e s s danger of c r a c k i n g and with improved ductility. The r o l e of the oxide was suggested to be that of inhibiting grain boundary s h e a r and m i g r a t i o n plus the pinning of dislocation tangles. M. S. GREWALis Group Manager, Advanced Processingand Control, Research and Development Laboratory, Gillette Company, Boston, Mass. S.A. SASTRIis Group Manager, MaterialsResearch Division,Gillette Company, Boston, Mass.,and N. J. GRANT is Director, Center for MaterialsScienceand Engineering,and Professor, Department of MaterialsScienceand Engineering,Massachusetts Institute of Technology,Cambridge,Mass. 02139. Manuscript submitted June 20, 1974. METALLURGICALTRANSACTIONSA
The c u r r e n t investigation was undertaken with a view of gaining a b e t t e r understanding of the r e l a t i o n s h i p b e tween the s t r u c t u r a l changes brought about by v a r i o u s TMTs in a Ni-1 vol pct BeO and a Ni-4.5 Mo-30 Co2 vol pct BeO alloy, and the accompanying changes in the high t e m
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