  In this work, Ni50Al50 alloy is taken into consideration as potential brazing
material for joining ZrB2 ultra-high temperature ceramic. The results of
experimental study on high temperature interfacial phenomena between molten
binary Ni50Al50 alloy and polycrystalline ZrB2, are shown. A sessile drop
method combined with a capillary purification procedure was applied to
investigate the wetting behavior of Ni50Al50/ZrB2 couple during holding for 400
seconds at temperature of 1688{\deg}C (i.e. at T=1.02Tm). It was found that the
molten Ni50Al50 rapidly wets and spreads over the surface of ZrB2, while
involved reactive infiltration into the solid substrate allowed reaching a
final contact angle of ~0{\deg} in 250 sec. The wetting kinetics was much
faster than that reported in the literature for Cu, Ag or Au tested at
T=1.05Tm. The solidified couple was subjected to SEM/EDS microstructural
characterization in order to reveal a course of interfacial phenomena. The
results point towards (I) an existence of Ni-enriched Ni-Al/ZrB2 surface
interfacial layer; (II) a formation of infiltration zone assisted by reactively
formed Al2O3 due to a reaction with Al-rich melt and (III) a partial transfer
of ZrB2 phase to Ni50Al50 alloy by a dissolution/precipitation mechanism.
