In the framework of joining processes of ultrahigh temperature ceramics (UHTCs), sessile drop experiments were performed in the Ni–B/ZrB2 system in the range 1110° ≤ T ≤ 1200 °C. They show that, at temperatures between 1110 and 1150 °C, isothermal solid–liquid transitions occur in a sequence; while in fact at T ≥ 1200 °C, the drop melts without any further phase transition, at lower temperatures, complete melting is followed by a solidification stage and final remelting. This complex behavior, which can be very relevant when utilizing Ni–B alloys for brazing processes (e.g., by the transient liquid phase bonding technique), is successfully interpreted on the basis of the complete B–Ni–Zr phase diagram newly computed by CALPHAD: Isothermal sections, calculated between 1110 and 1150 °C, show that the composition of the drop enters, crosses, and leaves the primary solidification region of the Zr2Ni21B6 ternary compound. The use of thermodynamic modeling for the explanation of experimental data sets a link between wetting and joining experiments and phase diagrams assessment.
Contact Angle Isothermal Section Ternary Compound Drop Height Liquid Transition
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Dr. P. Manfrinetti (DCCI, the University of Genoa) and Mr. A. Risplendente (Department of Earth Sciences, the University of Milan) are acknowledged for their help in preparing alloys and performing WDS analyses. The authors wish to thank Mr. Francesco Mocellin (CNR-IENI) for his technical support. This work was part of the Project “JoinHT” funded by the “CARIPLO Funding Scheme—2010.”