Materials exhibiting gas permeable porosity are of particular interest for a number of functional applications. Here, the authors show a new nanoporous superalloy membrane, far surpassing existing gas permeable porous metals in fineness and regularity of the porosity. This may not only open the path for new medical applications it may also help realizing the vision of miniaturized fuel cells powering laptops and cellular phones.
This paper reviews our current research activities on developing new multiphase metallic materials for structural applications with a temperature capability beyond 1,200ºC. Two promising material systems have been chosen: fi rst, alloys in the system Mo-Si-B which have demonstrated potential due to their high melting point of around 2,000ºC and due to the formation of a protecting borosilicate glass layer on the surface at temperatures exceeding 900ºC; and second, novel Co-Re-based alloys which have been chosen as a model system for complete miscibility between the elements cobalt and rhenium, offering the possibility of continuous increases of the melting point of the alloy through rhenium additions.
Four Ni-Mn-Ga single crystals exhibiting modulated 10M and 14M martensites were exposed to rotating magnetic fields of 1 and 2 T. Large periodic magnetic-field-induced strains were obtained for crystals that had been subjected to a mechanical stress while the martensite formed on cooling and to deformation in a magnetic field prior to the experiments with rotating field. A reduction of the magnetic-field-induced strain and fracture occurred when the field-induced strain was close to the transformation strain whereas a constant magneto-mechanical response was detected over more than 10 million field cycles when the field-induced strain was small. The cyclic magneto-mechanical response is related to the interaction of groups of twinning dislocations and twin boundaries. If the dislocations move in large groups, they nucleate cracks at twin boundaries. If the dislocations move in small groups, no cracks are formed resulting in a long lifetime.
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