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The size and the character (low and large angle, special boundaries, tilt and twist boundaries, twins) of the grain boundaries (GBs) in polycrystalline materials influence their strength and their fracture toughness. Recent studies devoted to nanocrystalline (NC) materials have shown a deviation from the Hall-Petch law. Special GBs formed by Σ3 twins in(More)
1. Abstract The present study proposes a comparison between several martensitic and ferritic steels in terms of creep strength and cyclic softening effect. The damage mechanisms are identified using fractographic observations and the microstructural evolutions are observed by TEM. The effects of a modified chemical composition on the high temperature(More)
A methodology for measuring the fracture toughness at crack initiation and the crack extension resistance of the molten zone of resistance spot welds under Mode I loading has been developed. The cross tensile test of U-shaped specimens was modified by crack growth monitoring and stress intensity factor determination. The resulting values of fracture(More)
The development of Generation IV fission nuclear reactors and fusion nuclear reactors requires materials able to resist to high temperature (650°C) creep, but also to creep-fatigue. Martensitic 9-12%Cr steels are candidate materials for these applications. Recent studies on commercial P91 steel showed that cyclic loadings coupled to high-temperature creep(More)
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