Enhancement of diffusion in deformation-induced non-equilibrium grain boundaries

Author： Kornelyuk Lida G. Lozovoi Alexander Yu. Razumovskii Igor M.

ISSN： 0141-8610

Source： Philosophical Magazine. A. Physics of Condensed Matter. Defects and Mechanical Properties, Vol.77, Iss.2, 1998-02, pp. : 465-474

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Abstract

The nature of the non-equilibrium state of grain boundaries (GBs ) is investigated using a Ni-based superalloy with a microduplex gamma + gamma microstructure which is stable against the grain growth at low temperatures by means of a direct diffusion experiment. The diffusion penetration profiles (63Ni) in the as-annealed and pre-cold-deformed (10%) states of the alloy have been measured by the residual activity techniques. The influence of a number of factors (temperature, time of diffusion anneal and time of preliminary anneal ) on the shape of the penetration profiles has been investigated. The profiles for the temperatures above 923 K exhibit a single part associated with GB diffusion with an almost constant slope- (ln c ) / y6/5. Below 923 K the GB-related region of the profiles for the pre-cold-deformed samples exhibits two distinct parts with different slopes. The deeply penetrating parts of these profiles are associated with diffusion along non-equilibrium GBs, which disappear after pre-annealing at higher temperatures. On the basis of the diffusion data obtained, the non-equilibrium state of GBs is identified as a metastable state and the process of relaxation of the non-equilibrium GB structure is interpreted as a structural phase transformation.