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Liquid‐Film‐Assisted Formation of Alumina/Niobium Interfaces

“…Bonding temperature and bonding pressure were varied. A comparison of work by Shalz et al [19] (1150°C, 5.1 MPa) and that of Marks [26,52,53] (1150°C, 2.2 MPa and 7.5 MPa) suggests that increasing the pressure at 1150°C led to higher average fracture strength and reduced scatter. The improved strength characteristics appeared to correlate with more complete breakup of the copper film, which was initially ≈3 µm thick in all three cases.…”

“…In bonds with polycrystalline alumina, the degree of film breakup appeared to be higher, suggesting that alumina grain boundaries and cavities may help initiate breakup [26]. Comparison of fracture surfaces from interfacial failures in bonds prepared at 1400°C from a relatively coarser (≈20-25 µm) and a finer (≈1 µm) average grain size alumina also suggested that the alumina grain boundaries and the grain boundary periodicity influenced the film evolution and fracture surface topography [53].…”

“…Experiments by Marks et al. [26,52,53] demonstrated that increasing the processing temperature to 1400°C while maintaining a bonding pressure of ≈2.2 MPa produced samples with high average room-temperature bend strength (240 MPa), a narrow strength distribution (standard deviation ±18 MPa), and a roughly 3:1 ratio of ceramic to interfacial failures.…”

“…The present work is part of a broader effort [26,52,53] to examine the effects of processing conditions on joint properties and to establish fundamental processingmicrostructure-property relationships for this system. This paper provides the first direct comparison of the strength and fracture behavior of alumina/niobium interfaces (joints) prepared at the same temperature (1400°C) and applied pressure (≈2.2 MPa) by conventional solid-state diffusion bonding and by liquidphase-assisted diffusion bonding.…”

“…The diffusion bonding of these materials, their interfacial structure, chemical compatibility, strength and failure characteristics, and the influence of interfacial impurities have all been examined and reported extensively in the literature . Extensive discussions can be found in prior publications [19,26,52,53]. For the present purposes, a brief review of diffusion bonding conditions, interface microstructure evolution, and fracture properties is provided.…”