On the kinetics of rafting in CMSX-4 superalloy single crystals
1999; Elsevier BV; Volume: 47; Issue: 7 Linguagem: Inglês
10.1016/s1359-6454(99)00093-2
ISSN1873-2453
AutoresNarumol Matan, David Cox, C.M.F. Rae, Roger C. Reed,
Tópico(s)Aluminum Alloy Microstructure Properties
ResumoThe kinetics of γ′ rafting in CMSX-4 single crystals at 950°C has been studied using scanning and transmission electron microscopies. The crept material was subjected to further heat treatment in the absence of applied stress, in order to deduce the threshold strain ϵth for rafting to continue; this is shown to be 0.10±0.03%. For strains smaller than ϵth, rafting occurs exceedingly slowly; once ϵth is exceeded the kinetics are largely unaffected by the absence of applied stress. The magnitude of ϵth confers a reduction in γ/γ′ interfacial coherency and a relaxation of interfacial misfit stresses. It is concluded that the threshold strain is a quantity suitable for distinguishing between rafting occurring in the “elastic” and “plastic” regimes. The results confirm conclusively that plasticization of the horizontal γ-channels by (a/2)〈110〉{111} creep dislocations and their subsequent adsorption at the γ/γ′ interfaces, with a concomitant loss of perfect coherency and reduction in elastic misfit strains, is responsible for providing the kinetic path which enables rafting to occur at a reasonable speed. An argument is put forward to explain the magnitude of ϵth.
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