Creep-rupture in powder metallurgical nickel-base superalloys at intermediate temperatures

Journal Article · Sat Mar 01 04:00:00 EST 1980 · Metall. Trans., A; (United States)

DOI:https://doi.org/10.1007/BF02654573· OSTI ID:5418528

Law, C C; Blackburn, M J

To gain insight into the factors which control the creep-rupture properties of powder metallurgical nickel-base superalloys at intermediate temperatures (650 to 775/sup 0/C), a comparative study was conducted on the alloys AF115, modified MAR-M432 (B6) and modified IN100 (MERL76). Creep-rupture properties in these alloys were characterized in terms of the stress and temperature dependence of the secondary creep rate, epsilon/sub S/, and rupture time, t/sub R/. Within the limited stress ranges used, the stress dependence of both epsilon/sub S/ and t/sub R/ at 704/sup 0/C can be represented by power laws epsilon/sub S/ = C sigma/sup n/ and t/sub R/ = M sigma/sup -p/; where C, M, n, and p are constants. The stress exponents n and p are approximately equal for both AF115 and B6 with values of 16 and 7, respectively. In the case of MERL76, n and p are different, with values of 15 and 5, respectively. The apparent activation energies, Q, are 700, 370, and 520 K J mol/sup -1/ for AF115, B6, and MERL76, respectively. For these alloys, long creep-rupture lives are associated with large values of n and Q. The significant differences in n and Q values between AF115 and B6 were related to creep recovery processes for which the lattice misfit between the gamma and the gamma prime was identified to be an important parameter. However, the unequal n and p values in MERL76 compared with those in AF115 and B6, were traced to differences in fracture mode. Failures in AF115 and B6 were initiated at carbide particles at grain boundaries. In contrast, fracture in MERL76 was initiated at grain boundary triple junctions. The rupture lives of AF115 and B6 can be modeled reasonably well by the growth of cavities during secondary creep and propagation of a surface-nucleated crack during the tertiary creep.

• Research Organization: Pratt and Whitney Aircraft, East Hartford, CT
• OSTI ID: 5418528
• Journal Information: Metall. Trans., A; (United States), Journal Name: Metall. Trans., A; (United States) Vol. 11:3; ISSN MTTAB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
CREEP
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DISLOCATIONS
FABRICATION
FAILURES
HOT PRESSING
LINE DEFECTS
MATERIALS WORKING
MECHANICAL PROPERTIES
METALLURGY
MICROSTRUCTURE
NICKEL ALLOYS
NICKEL BASE ALLOYS
PARTICLE SIZE
POWDER METALLURGY
PRESSING
RUPTURES
SIZE
STACKING FAULTS
TENSILE PROPERTIES