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Grain boundary self-diffusion of63Ni in pure and boron-doped Ni3Al

Authors
Journal
Intermetallics
0966-9795
Publisher
Elsevier
Publication Date
Volume
4
Issue
8
Identifiers
DOI: 10.1016/0966-9795(96)00058-1
Keywords
  • A. Intermetallics
  • Nickel Aluminides
  • Based On Ni3Al
  • B. Diffusion
  • D. Grain Boundaries
  • F. Trace Element Analysis

Abstract

Abstract Grain boundary (gb) self-diffusion in pure Ni-rich Ni 3Al was measured between 882 and 1374 K using the radiotracer 63Ni, a serial sectioning technique and sensitive liquid scintillation counting. The results of the gb diffusivity P = δD gb (δ : gb width, D gb : gb diffusion coefficient) can be represented by the Arrhenius parameters P 0 = 3.27 · 10 13 and Q gb = 168 kJ mol . Additionally gb diffusion was investigated in boron-doped (0.24 at%) Ni-rich Ni 3Al in the range from 882 to 1352 K yielding P 0 = 1.24 · 10 −12 m 3/s and Q gb = 187 kJ mol . The increase in the activation enthalpy Q gb and the decrease of P upon boron-doping is explained by the segregation of B in Ni 3Al gbs, which may lead to an increase in the vacancy formation enthalpy and to a blocking of energetically favourable diffusion paths in the gbs. For comparison gb self-diffusion in pure Ni was remeasured yielding Q gb = 112 kJ mol . Ordering of the lattice and the preservation of ordering up to the gb planes, as predicted in Ni 3Al, therefore has a pronounced decelerating influence on gb diffusion, stronger than on bulk diffusion. Applying the semi-empirical relation of Borisov et al. ( Phys. Met. Metallogr., 17 (1964) 80) gb energies γ gb were determined for arbitrary high angle gbs in pure and B-doped Ni 3Al, resulting in 915 and 870 mJ/m 2, respectively, at 1100 K.

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