Tadashi Igarashi1 and Mitsuo Osada1
1R & D Group, Sumitomo Electric Industries, Ltd., Itami
Ag-Ni alloys containing fibrous Ni phase of 15∼40 mass% prepared by drawing of sintered alloys were oxidized at 923 to 1073 K in air. The depth of the internally oxidized layer, ξ , was measured and microstructures were observed in order to investigate the behavior of internal oxidation of two phase alloys.
The results obtained are as follows:
(1) The fibrous structure was disintegrated during internal oxidation, when the specimens were oxidized in a direction parallel to fibrous Ni phase. In an alloy with NNi=0.55 (NNi means mole fraction of Ni), cell-structure of oxide was formed.
(2) Oxides stretching in the direction of the fibrous structure of the alloy were dispersed in the alloy with NNi=0.245, while wavy lamellae of oxide were formed in the alloy with NNi=0.38, when specimens were oxidized in the direction of fibrous Ni phase.
(3) The relation between the depth of the internally oxidized layer and the oxidation time was shown by a parabolic law at every temperature with NNi=0.38. But the growth of internally oxidized layer with NNi=0.55 deviated from a parabolic law above 873 K.
(4) The parabolic rate constant of internal oxidation in a direction parallel to the fibrous structure, k//, was larger than that in a direction vertical to the fibrous structure, k⊥, at every temperature and in every Ni content.
(5) The permeability (product of oxygen content at the surface of an alloy and its diffusion coefficient) of oxygen in the internally oxidized layer was accelerated by the effect of the continuous interface of Ag and NiO extending in the direction of fibrous Ni phase, while it was disterved by the lamellae of oxide lying vertically to the oxidation direction.
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