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Bonding Structure of Zirconium Diboride Joined with Filler Alloys Bearing Active Metals

1990; Japan Institute of Metals and Materials; Volume: 54; Issue: 7 Linguagem: Inglês

10.2320/jinstmet1952.54.7_832

1880-6880

Takeo Sakurai, Tomoya MINEGISHI, Shōtaro Morozumi, Kazuo Hamajima,

Advanced ceramic materials synthesis

Bonding structures of zirconium diboride, ZrB2, Joined to active metals, Ti, Zr and Hf, containing alloys, were investigated by optical microscopy. EPMA and X-ray diffraction methods. The results obtained are as follows:(1) When a Cu/active metal/Cu three-foil filler was used for brazing at temperatures between 1273 and 1673 K for 1200 s and at 1273 K for 600 to 3600 s, the active metal migrated and segregated at the bonding interface of the brazing metal and ZrB2. The thickest active-metal-segregated layer was obtained in the joint bonded with Ti containing the filler alloy, even though the standard free energy of formation of boride is the highest in Ti of the other three IVa transition group metals.Since the Ti-segregated layer increased linearly with the increase of temperature and time, it was deduced that the Ti atom might migrate as a cation in the molten or solid filler alloys by any electric motive force.(2) When an Al/active metal/Al foil filler was used for brazing at 1173 K for 1200 s, the active metal also migrated and segregated at the bonding interface, though the segregated layer was very thin in comparison with that in the Cu filler alloy. This thin layer was thought to be due to the low brazing temperature at which the solubility of Ti in liquid Al is very limited.(3) When Ni/active metal/Ni foil fillers were used for brazing at 1473 K for 1200 s, joining was carried out by solid state diffusion bonding. The segregation of the active metal at the bonding interface was observed, accompanied by diffusion of Ni into the ZrB2 matrix.