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[en] High resolution power autography of radioactive ³⁵S was used to measure the volume and intergranular heats of activation of sulphur diffusion into a high purity and a less pure, industrial Inconel 600 (a 77/16/7 nickel, chromium, iron alloy). Neither purity nor initial microcrystalline structure affected the volume heat of activation, which was 217.36+-1.25 KJ/mol, whereas there were significant differences of the intergranular heats of activation both with pure and impure specimens and with and without sulphuric acid etching. The following values were obtained for the high purity specimens: -319.77 KJ/mol (recrystallized) and -213.18 KJ/mol (sulphuric acid etched), and for the industrial specimens: -252.89 KJ/mol (recrystallized) and -110.77 KJ/mol (sulphuric acid etched). (R.S.)

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[en] Inconel 600 (a 77/16/7 nickel, chromium, iron alloy) is being used for the bundles of tubes of pressurized water nuclear reactors. Hence, this study of the effect of sulphur in the surrounding atmosphere on grain penetration and mechanical strength. H₂/H₂S was found to be more reactive than SO₂, with partial pressure of sulphur temperature and duration of exposure as the important parameters. There was always grain penetration with a H₂/H₂S atmospheres. At sulphur partial pressure of more than 3 at, Cr₂S₅ and Ni₃Si₂ were formed. At 645⁰C the eutectic Ni+Ni₃S₂ formed a liquid phase. At sulphur partial pressures between 10^-12 and 10^-6 at in H₂/H₂S, Cr₃S₄ was found in grain boundaries, but no nickel sulphide. From 10^-9 and 10^-8 at of sulphur partial pressure a thin film of chromium sulphide is formed of 5 to 10 μm. This propagates dislocations of the chromium and nickel grains to a depth of 200 to 300 μm. Oxides precipitated at grain boundaries favoured the penetration of elemental sulphur. Carbides, going into solution at 900⁰C, blocked the penetration of both sulphur and sulphides. At 800⁰C, in the presence of carbides and oxides, the penetration varied linearly with the time of sulphurization, whereas at 900⁰C the depth of penetration came to a halt within 2 hours, which was the time required to dissolve the carbides. At -196⁰C, neither carbides nor sulphides in the grain boundaries affect the ductility. The joint action of carbides or oxycarbides and sulphides was required for intergranular fracture. It was impossible to state the element or elements with which the sulphur brings about interactions which lead to fracture. (Auth.)

[en] Interfacial diffusion has been evidenced in a eutectic-like Ni, Cr-TaC composite, using high resolution autoradiographic techniques. The structure of the fibre-matrix interface has been determined by using high voltage electron microscopy. The fibre-matrix interface has been shown to be a diffusion short circuit in the temperature range 700⁰C to 900⁰C. (author)

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