Rafting in superalloys

Journal Article · Fri Mar 01 04:00:00 EST 1996 · Metallurgical Transactions, A

DOI:https://doi.org/10.1007/BF02648942· OSTI ID:237765

Nabarro, F R.N. ^[1]

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1. Univ. of Witwatersrand, Johannesburg (South Africa)

The phenomenon of rafting in superalloys is described, with particular reference to modern superalloys with a high volume fraction of the particulate {gamma}{prime} phase. It is shown that in the elastic regime, the thermodynamic driving force for rafting is proportional to the applied stress, to the difference between the lattice parameters of the {gamma} matrix and the {gamma}{prime} particles, and to the difference of their elastic constants. A qualitative argument gives the sign of this driving force, which agrees with that determined by Pineau for a single isolated particle. Drawing on the work of Pollock and Argon and of Socrate and Parks, it is shown that after a plastic strain of the sample of order 2 {times} 10{sup {minus}4}, the driving force is proportional to the product of the applied stress and the lattice misfit, in agreement with the results of the calculations of Socrate and Parks. The rate of rafting is controlled by the diffusion of alloying elements. Here, the tendency of large atoms to move from regions of high hydrostatic pressure to those of low may outweigh the influence of concentration gradients. The deformation of the sample directly produced by rafting is small, of order 4.5 {times} 10{sup {minus}4}. The rafted structure is resistant to creep under low stresses at high temperatures. Under most experimental conditions at relatively high stresses, rafting accelerates creep; this effect may be less pronounced at the small strains acceptable under operational conditions.

• Sponsoring Organization: USDOE
• OSTI ID: 237765
• Journal Information: Metallurgical Transactions, A, Journal Name: Metallurgical Transactions, A Journal Issue: 3 Vol. 27; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

33 ADVANCED PROPULSION SYSTEMS
36 MATERIALS SCIENCE
CREEP
CRYSTAL STRUCTURE
DEFORMATION
DIFFUSION
ELASTICITY
HEAT RESISTING ALLOYS
INTERMETALLIC COMPOUNDS
LATTICE PARAMETERS
MICROSTRUCTURE
PARTICULATES
STRAINS
STRESSES
THERMODYNAMICS
TURBINE BLADES