-The fracture surfaces of a Zr-based bulk metallic glass exhibit exotic multi-affine isotropic scaling properties. The study of the mismatch between the two facing fracture surfaces as a function of their distance shows that fracture occurs mostly through the growth and coalescence of damage cavities. The fractal nature of these damage cavities is shown to control the roughness of the fracture surfaces. [17,18] have shown to be self-affine, with a roughness exponent ζ ≈ 3/4 in spite of huge differences in the fracture mechanisms. It was therefore suggested [5,19] that ζ might have a universal value, i.e., independent of the fracture mode and of the material.More recently, it has been shown [11,13] that fracture surfaces are anisotropic, i.e. when profiles along the direction of crack propagation are considered, the roughness exponent is equal to β 0.6. Bonamy et al. [12] have shown that the set of exponents {ζ 0.75, β 0.6} define a universality class corresponding to length scales smaller than the process zone size, where non linear elastic processes take place. Above this process zone size, another university class is observed [12,20,21] characterized by a set of exponents {ζ 0.4, β 0.5} that can be understood theoretically within the Linear Elastic Fracture Mechanics framework.A third regime arises at very small length scales, characterized by a roughness index close to ζ ≈ 0.5, observed in a metallic alloy and in a soda-lime silicate glass [8][9][10] along a direction perpendicular to the direction of crack propagation. This regime was suggested [22] to be

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Microstructural instabilities occurring in two new generation single crystal nickel-based superalloys containing additions of both Re and Ru have been characterised by means of electron backscatter diffraction (EBSD). Cellular colonies develop in the MC632 experimental alloy at subgrain boundaries with misorientations higher than 10°. The role of these microstructural instabilities in the mechanical behaviour was investigated. After creep at high temperature microcracks are observed at the limit of the cellular colonies but these defects are not more frequent than those initiating from micropores or within the dendrites. As only a low volume fraction of γ-γ' alloy is involved in this transformation, the influence of this phenomenon on the alloy creep strength is negligible. Secondary reaction zones (SRZ) were observed beneath Pt-modified aluminide coating in the MC544 superalloy. EBSD analysis clearly demonstrated the polycrystalline structure of these SRZ. Despite the presence of internal grain boundaries, the SRZ are not preferential sites for premature failure initiation. However, the stress-rupture life is adversely affected by the reduction of the load-bearing section of safe γ-γ' alloy. The decrease of low cycle fatigue (LCF) strength observed at 650°C for coated MC544 compared to the bare alloy was mainly attributed to premature crack initiation within the aluminide coating and not from the SRZ. During LCF tests at 950°C of coated MC544, numerous cracks also initiate from the aluminide coating but then remain restricted to the SRZ area. The failure initiates at internal casting porosities. The slight LCF strength reduction observed in these conditions was attributed to the load bearing section reduction of unaffected γ-γ' alloy.

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