Isothermal solid-liquid transitions in the (Ni,B)/ZrB2 system as revealed by sessile drop experiments

In the framework of joining processes of Ultra High Temperature Ceramics (UHTCs), sessile drop experiments were performed in the Ni-B/ZrB2 system in the range 1110\ub0 64T 641200\ub0C. They show that, at temperatures between 1110 and 1150\ub0C, isothermal solid-liquid transitions occur in a sequence; while in fact at T 651200\ub0C the drop melts without any further phase transition, at lower temperatures complete melting is followed by a solidification stage and final re-melting. This complex behaviour, 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\ub0C, show that the composition of the drop enters, crosses and leaves the primary solidification region of the Zr2Ni21B6 ternary compound. The use of thermodynamic modelling for the explanation of experimental data sets a link between wetting and joining experiments, and phase diagrams assessment

Brazing transparent YAG to Ti6Al4V: Reactivity and characterization

none5noThe YAG/filler/Ti6Al4V system has been studied for the first time with the aim of producing brazed optical windows. Different fillers (AgCuTi, AgCu, Ag) and temperatures have been taken into account and the interfacial zones of the samples have been evaluated in terms of morphology and compositions. A thin and continuous metal-ceramic layer containing Ti is formed in contact with the YAG ensuring the adhesion between all the joined materials. The best joining results have been obtained at 850. °C, where we have observed the formation of an interfacial CuTi layer when AgCuTi and Ag have been used. No intermetallic compound formation was observed using the pure Ag at 970. °C and 1050. °C. The phase formation was interpreted using the CALPHAD method by means of recalculated Ag-Cu-Ti and Ag-Al-Ti isothermal sections. Microhardness tests have been conducted to evaluate the performances of the joints in terms of mechanical properties.Gambaro, S; Valenza, F.; Passerone, A.; Cacciamani, G.; Muolo, M.L.Gambaro, Sofia; Valenza, F.; Passerone, A.; Cacciamani, Gabriele; Muolo, M. L

Experimental investigations and thermodynamic modeling in the ZrB2-Ni section of the B-Ni-Zr system

Abstract An investigation of melting equilibria in the Ni-rich part of the Bsingle bondNisingle bondZr system was carried out by means of a combined experimental and computational approach, in order to improve the interpretation of wetting experiments of Bsingle bondNi alloys on ZrB2 substrates. Several samples along the Nisingle bondZrB2 vertical section, close to the Zr2(Ni21 12xZrx)B6 ternary phase, were prepared by arc-melting the pure metals; the samples were thoroughly studied by means of powder X-ray diffraction and SEM\u2013EDS, and then analyzed by DTA in order to obtain their transition temperatures. The results were used to improve the CALPHAD thermodynamic modeling of the Bsingle bondNisingle bondZr system. A solubility range of the ternary phase between x = 0.14 and x = 0.68 was detected, due to the mixing of Zr and Ni in the 4a crystallographic site

High-temperature-reactivity of Al–Ti alloys in contact with SiC

International audienceSeveral industrial processes involving SiC coupling to Al-Ti alloys (e.g. metallization of SiC components, brazing of SiC parts) require an in-depth knowledge of Al-Ti/SiC interactions occurring at high temperatures. To this end, the surface reactivity between SiC and Al-Ti alloys (Al3Ti and (Al+Al3Ti) systems) was analyzed by specific experiments (wetting, DSC, microstructural examinations) as well as by a thermodynamic approach (CALPHAD method). An Al-C-Si-Ti thermodynamic database was successfully established to calculate several sections and projections in order to compare the computed, expected solid phases formed at the interface with those characterized in wetting experiments. In this way, the change in liquid and solid phases was interpreted and discussed, defining the Ti3(Al,Si)C2 mixed MAX-phase as the main interfacial product created by thechemical reaction, as a function of temperature and alloy composition. This work constitutes a guide for the choice of operating parameters in processes such as brazing or SiC metallization in microelectronic applications, in which the control of interfacial products is one of the most delicate production steps. The approach proposed to monitor the pathway of liquid composition with time and temperature during liquid/solid interaction, successfully applied to interpret the microstructure obtained in wetting experiments, is a promising method for interpreting more complex cases such as homogeneous or even heterogeneous brazing processes