Abstract:Low‐cycle fatigue and corrosion fatigue mechanisms of ultra‐high‐purity (UHP) Ni and Ni‐base alloys in H2SO4 solutions are analysed. UHP materials are used to eliminate the impurity effects, including those on grain boundaries which can promote hydrogen embrittlement. Particular attention is paid to the conditions for hydrogen absorption and its effect on damage processes. Hydrogen embrittlement is analysed in terms of persistent slip band–grain boundary (PSB–GB) interactions and hydrogen diffusion short circu… Show more
“…In fact, similar experiments on polycrystals do not result in the formation of a stress plateau. Moreover, hydrogen grain-boundary diffusion together with stress concentrations due to the formation of PSB, would result in very fast crack propagation and fracture [21].…”
Section: Stress Corrosion Cracking -The Study Of Hydrogen-dislocationmentioning
The interest in ultra-high-purity (UHP) metals and alloys (including single crystals and bicrystals) in studying damage mechanisms is presented through three practical cases of environment or precipitation-induced damages in nuclear power plants. First, stress corrosion cracking mechanisms are assessed by direct measurements of hydrogen-dislocation interactions in pure nickel single crystals in low-cycle fatigue tests under cathodic potential. Hydrogen-induced softening is observed, that confirms an important assumption on the corrosion-enhanced plasticity model. Second, mechanisms of high-temperature intergranular cracking of bimetallic welds are analysed on a series of model materials including 302 H stainless steel and UHP stainless steel selectively doped with carbon. The key role of carbide precipitation and localised shearing in a chromium-depleted zone is pointed out. Finally, the analysis of intergranular penetration of liquid Bi-rich films in a polycrystalline solid Ni inducates the presence of very long and brittle films of nanometric thickness, which have to be taken into account in any model of liquid-metal embrittlement.
“…In fact, similar experiments on polycrystals do not result in the formation of a stress plateau. Moreover, hydrogen grain-boundary diffusion together with stress concentrations due to the formation of PSB, would result in very fast crack propagation and fracture [21].…”
Section: Stress Corrosion Cracking -The Study Of Hydrogen-dislocationmentioning
The interest in ultra-high-purity (UHP) metals and alloys (including single crystals and bicrystals) in studying damage mechanisms is presented through three practical cases of environment or precipitation-induced damages in nuclear power plants. First, stress corrosion cracking mechanisms are assessed by direct measurements of hydrogen-dislocation interactions in pure nickel single crystals in low-cycle fatigue tests under cathodic potential. Hydrogen-induced softening is observed, that confirms an important assumption on the corrosion-enhanced plasticity model. Second, mechanisms of high-temperature intergranular cracking of bimetallic welds are analysed on a series of model materials including 302 H stainless steel and UHP stainless steel selectively doped with carbon. The key role of carbide precipitation and localised shearing in a chromium-depleted zone is pointed out. Finally, the analysis of intergranular penetration of liquid Bi-rich films in a polycrystalline solid Ni inducates the presence of very long and brittle films of nanometric thickness, which have to be taken into account in any model of liquid-metal embrittlement.
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