Joining of UHTC Composites Using Metallic Interlayer
Ultra-high temperatures ceramics (UHTCs) are the subject of intense worldwide research effort, and their stability in severe environments makes them candidates for aerospace, nuclear and solar energy applications. Widespread usage UHTCs requires the devel
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Joining of UHTC Composites Using Metallic Interlayer Noritaka Saito, Laura Esposito, Toshio Yoneima, Koichi Hayashi, and Kunihiko Nakashima
Abstract Ultra-high temperatures ceramics (UHTCs) are the subject of intense worldwide research effort, and their stability in severe environments makes them candidates for aerospace, nuclear and solar energy applications. Widespread usage UHTCs requires the development of effective and reliable joining methods that facilitate the fabrication of large, complexshaped, and potentially multimaterial components and devices. Joining of HfB2 and ZrB2, UHTC diborides, which exhibit outstanding thermo-mechanical and thermochemical properties and good erosion and corrosion resistance, was the focus of the present study. MoSi2 is an effective sintering aid and a composite component for both HfB2 and ZrB2, resulting in dense bulk materials with excellent mechanical properties. HfB2–10 vol.% MoSi2 composites were joined at 1500 °C with a Ni/Nb/ Ni interlayer that forms a thin liquid film. Joint-region characterization revealed well-bonded interfaces with interfacial reaction products with the MoSi2. Well-bonded interfaces were also obtained for a ZrB2–10 vol.% MoSi2 composite bonded at 1500 °C with both Ti and Zr interlayers. It was found that the Ti interlayer exhibited more intensive interfacial reaction with ZrB2 composite than the Zr interlayer. Additionally, well-bonded interfaces were also found for a ZrB2–10 vol.% MoSi2 composite bonded at 1500 °C with ZrB2-X vol.% Ni (X = 20, and 40) powder-based interlayer. Joint-region characterization revealed well-bonded interfaces with microstructures strongly dependent on the Ni content. Keywords Ultra-high temperature ceramics • Joining • Transient liquid phase • Interfacial reaction • Four-point bending test
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Introduction
The attractive and unusual properties that can be exhibited by ultrahigh temperature ceramics (UHTCs) have made them appealing candidate materials for a wide range of applications, including ones in the nuclear, solar, and aerospace sectors. The ultrarefractory borides, (e.g., ZrB2, TiB2 and HfB2), like the ultrarefractory carbides, are difficult to sinter in undated form, and for both types of UHTCs, the use of modest amounts of an appropriate sintering aid has played a key role in facilitating densification (even in the absence of an applied pressure), refining the microstructure, and improving properties. For the specific case of ZrB2, additions of MoSi2 have produced the desired processing and microstructural benefits, and thereby, have drastically improved the mechanical performance [1–4]. Applications often require that components be joined. This has many practical advantages. It allows the fabrication of complex-shaped structures, and for multimaterial structures, can allow costly high-performance materials to be used selectively and judiciously, where they are most needed. Prior work [5–7] has demonstrated the feasibility of a transient-liquidphase (TLP) inspired approach to joining undoped ZrC, HfC, and Ta
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