Microstructure and phase stability of INCONEL alloy 617
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INCONEL*a l l o y 617
is a nickel-chromium-cobalt-
*INCONELis a registeredtrademarkof The InternationalNickelCompany, Inc.
A l l s p e c i m e n s w e r e f r o m one h e a t ; the c h e m i c a l c o m p o s i t i o n is given in T a b l e II. The m a t e r i a l was p r o d u c e d a s 0.750 in. (19 m m ) d i a m h o t - r o l l e d r o d
molybdenum alloy characterized b y good cyclic-oxidation resistance at 2000~ (1093~ and high creep-rupture strength at temperatures from 1200~ (649~ to 2000~ (I093~ The alloy is solid-solution-strengthened and is used in the annealed condition. Alloy 617 exhibits a strengthening response during extended exposure to intermediate temperatures. As shown in Fig. 1, the microstructure of the alloy after such exposure contains copious amounts of precipitate in both grain-boundary and intragranular areas. The work reported here was done to identify the phases present, to determine the stability of the phases, and to investigate the strengthening mechanisms by correlating microstructures with mechanical properties. EXPERIMENTAL PROCEDURE C r e e p s p e c i m e n s w e r e s e l e c t e d for the s t u d y b e c a u s e t h e y would p r o v i d e a c l o s e a p p r o x i m a t i o n of m a t e r i a l e x p o s e d to t e m p e r a t u r e under l o a d in a c t u a l s e r v i c e . The s p e c i m e n s w e r e 0.252 in. (6.35 ram) d i a m with a 2.25 in. (57.2 ram) gage length. T a b l e I l i s t s t e m p e r a t u r e s , s t r e s s e s , and e x p o s u r e t i m e s f o r the s p e c i m e n s . The m a x i m u m a m o u n t of p l a s t i c s t r a i n r e c o r d e d for any s p e c i m e n was 9.39 pct, and the c r e e p c u r v e s i n d i c a t e d that none of the s p e c i m e n s had begun t e r t i a r y creep. W. L. MANKINS, J. C. HOSIER, and T. H. BASSFORD are Metallurgical Project Leaders and Chief Mechanical Testing Engineer, respectively, Huntington Alloy Products Division, The International Nickel Company, Inc., Huntington, W. Va. 25720. Manuscript submitted October 26, 1973. METALLURGICAL TRANSACTIONS
Fig. 1--Microstructure of creep-test specimen subjected to 1400~ (760~ and 15 ksi (103 MPa) for 10,330.5 h. Magnification 500 times. Specimen No. 2. VOLUME 5,DECEMBER 1974-2579
Table I. Creep-Test Conditions to Which Samples Were Exposed Prior to Metallographic Study
Temperature
Stress
SpecimenNo.
~
~
psi
MPa
Duration,* h
1 2 3 4 5 6
1200 1400 1500 1600 1800 2000
649 760 816 871 982 1093
35,000 15,000 10,000 4,000 3,000 1,000
241 103 69 28 21 7
956.0 10,330.5 3,023.0 666.3 379.4 215.3
*Alltestswere discontinuedbeforerupture.
Table II. Chemical Composition, Wt Pet, of Material Studied
Chromium Cobalt Molybdenum Aluminum Titanium Carbon Nickel
22.51 12.67 8.91 1.05 0.41 0.07 Remainder
and was given a t r e a t m e n t of 2150~ (1177~ h, a i r cool, b e f o r e b e i n g c r e e p - t e s t e d . Samples for optical m i c r o s c o p y w e r e p r e p a r e d f r o m the gage length of each c r e e p s p e c i m e n . The s a m p l e s , ab
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