M. Galano

3D Studies of Indentation by Combined X-Ray Tomography and Digital Volume Correlation

Hardness testing obtains material properties from small specimens via measurement of load-displacement response to an imposed indentation; it is a surface characterisation technique so, except in optically transparent materials, there is no direct observation of the assumed damage and deformation processes within the material. Three-dimensional digital image correlation (digital volume correlation) is applied to study deformation beneath indentations, mapping the relative displacements between high-resolution synchrotron X-ray computed tomographs (0.9 μm voxel size). Two classes of material are examined: ductile aluminium-silicon carbide composite (Al-SiC) and brittle alumina (Al2O3). The measured displacements for Hertzian indentation in Al-SiC are in good agreement with an elastic-plastic finite element simulation. In alumina, radial cracking is observed beneath a Vickers indentation and the crack opening displacements are measured, in situ under load, for the first time. Potential applications are discussed of this characterization technique, which does not require resolution of microstructural features.

Creep behaviour of a FeSi-base metallic glass containing nanocrystals

Abstract Amorphous Fe73.5Cu1Nb3Si13.5B9 in isoconfigurational steady state and partially crystalline samples of the same material, obtained by controlled devitrification, were deformed under tensile creep tests in the stress range 100–800 MPa and temperatures between 723 and 753 K. Strain rate sensitivity and apparent activation energy were also measured by means of differential tests.

Effect of Nb on nanoquasicrystalline Al-based alloys

Nanoquasicrystalline Al-based alloys, containing icosahedral particles in an α-Al matrix, exhibit high strength at elevated temperature. The metastability of the quasicrystals can limit the use of these alloys. In the present work, the microstructural evolution of Al93(Fe3Cr2)7 and Al93Fe3Cr2Nb2 (at%) alloys was studied using heat treatments and structural characterization by XRD, TEM and STEM-EDX analysis. It was observed that the Nb is dissolved in the Al–Fe–Cr icosahedral phase. This provides higher thermal stability, retaining the fine nanoquasicrystalline microstructure for longer times at high temperature.

Rapidly quenched Mg65AlxCu25-xMM10(MM: mischmetal) alloys

Abstract The ductility of the amorphous Mg–Cu–RE (RE: rare earths) alloys could be improved by means of the partial substitution of Cu atoms by Al ones, as can be inferred from the heterogeneous amorphous concept [1] , [2] . Instead of only one RE element, a solid solution of RE known as mischmetal (MM) was used. Rapidly quenched (RQ) samples (cooling rate > 10 3 K s −1 ) of Mg65AlxCu25−xMM10 (0⩽x⩽25 at.%) alloys were obtained in a splat cooling device. The structure and the crystallisation process were observed by means of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Fractographic analysis was carried out by scanning electron microscopy (SEM) on the fracture surface of samples broken by hand bending. With increase of the Al concentration, we observed that both the glass forming ability (GFA) and the amorphous pre-peak (a-pre-peak) in the XRD pattern decreased; meanwhile the crystallisation temperature increased. On the other hand, the ductility of the 10 at.% Al alloy was improved and a vein pattern was observed in the fracture surfaces.

Characterization of Casting Defects in Aluminium Alloys

In this paper, typical defects in aluminium alloys cast by conventional pouring of liquid metal into a cylindrical alumina crucible and an induction melting process are characterized by using macroetching, optical microscopy and scanning electron microscopy. Oxide film defects are generated in both processing methods. Oxide films formed during casting are a major type of defect observed in the microstructures of aluminium alloys products. It has been found that pouring of molten metal into a mould and induction stirring lead to different forms of oxide defects. Under induction stirring, such low-density entrained defects are found to be carried to near the surface of the liquid aluminium alloys and submerged surface oxide films become entangled.