Abstract:We have investigated the sliding friction behavior of metallic couples with different enthalpy of mixing or reaction by friction force microscopy. Comparing the friction behavior of miscible and immiscible couples we find that in the first case friction is governed by adhesion while the shear strength is low (τ = 3-6 MPa). In the latter case of immiscible couples, adhesion is found to be low and the shear strength is large (τ ≈ 70 MPa). Statistical analysis of atomic stick-slip images recorded on an Au(111) surface with tips of different affinities with gold allows for a deeper understanding of our results. The periodicity of atomic stick-slip images corresponds to the interatomic distance of gold for immiscible counter-bodies. In contrast, for a reactive couple the periodicity of atomic stick-slip significantly differs from the gold interatomic distance and may correspond to the structural length of an ordered intermediate phase at the tip-surface interface.

Thermally grown surface oxide layers dominate the single-asperity tribological behavior of a Zr 60 Cu 30 Al 10 glass. Increase in oxidation time leads to an increased contribution of shearing and a corresponding decreased contribution of ploughing to friction. This change in the dominating friction and wear mechanism results in an overall minor decrease of the friction coefficient of oxidized surfaces compared to the metallic glass sample with native surface oxide. Our results demonstrate the importance of creating a stable oxide layer for practical applications of metallic glasses in micro-devices involving sliding contact.

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This study presents a new seeding technique, named ‘interior seeding’ which allows the growth of a single REBCO (RE: rare-earth elements) grain in the interior of REBCO compacts. The key techniques of interior seeding are to provide appropriate open space for seeds in the interior of REBCO powder compacts to supply air or oxygen to the seeds, and to minimize the contact area between the seeds and liquid. The advantages of interior seeding are as follows: (1) simultaneous growth from the seed to the top and bottom of the REBCO compacts is possible, (2) fractions of the a-b growth sector and the a-c growth sector on the top surface can be controlled and (3) the top surfaces of the single-grain REBCO bulk superconductors are free from samarium or neodymium contamination from the used seeds. The very large single-grain Y1.5Ba2Cu3O7−y (Y1.5) bulk superconductors (42 mm) were successfully fabricated using a melt growth (MG) process combined with interior seeding. Also, large-grain Y1.5 bulk superconductors (41 mm) with 〈110〉/〈110〉 and 〈100〉/〈100〉 grain junctions were fabricated using multiple interior seeding. In this paper, the detailed process of interior seeding, the development of top surface patterns and the properties of single-grain Y123 bulk superconductors fabricated using interior seeding were reported.

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