| The Al₂O₃/STS304, Al₂O₃/Cu and Al₂O₃/Al₂O₃joints were vacuum-brazed with three types of Cu-Ag-Ti brazing alloy at 1193 K for 1.2 ks. The microstructure and microchemistry of reaction products formed at the Al₂O₃/braze alloy interface have been investigated by glancing x-ray diffractometer (G-XRD) and scanning electron microscope(SEM) equipped with energy-dispersive spectrometer (EDS). The reaction products of Al₂O₃/STS304 joint were a layered structure consisted of TiO (Monoclinic, ao=5.85Å, bo=9.34Å, co=4.14Å, Cu₂Ti₄O (Cubic, ao=11.49Å and Fe₂Ti₄O (Cubic, ao=11.297Å). For the Al₂O₃/Cu and Al₂O₃/Al₂O₃joints, reaction products were a layered structure consisted of TiO and Cu₂Ti₄O. For the Al₂O₃/STS304, Al₂O₃/Cu joints, the thickness of reaction product layer was in creased with Sn-addition and rapidly decreased with Al addition in Cu-Ag-Ti alloy. Type of reaction products was not varied with additional elements. The formation of TiO compound resulted from redox reaction between Al₂O₃and segregated Ti, but the Cu₂Ti₄O and Fe₂Ti₄O compounds was formed by solid-state reaction between TiO and Cu/Fe of brazing alloy and adhered metal respectively. The Cu₂Ti₄O and Fe₂Ti₄O compounds can be considered as (Cu, Fe)₂Ti₄O, because both of compounds have the nearly same crystal structure and lattice constant. That is, that compound seems to be formed as a result of the rearrangement of structure from monoclinic to cubic after the Cu and Fe atoms is diffused into the ordered vacant sites of pre-fomed titanium monoxide(TiO_(1±X), x=0.1). The formation of that compound means that the Cu and Fe atoms into TiO have the faster diffusion velocity than the other elements such as Ag, Al, Sn, Ni and Cr. Conclusively the thickness of reaction product layer depends on the diffusion velocity of metallic elements into the TiO layer and the additional elements in Cu-Ag-Ti brazing alloy effectuate the variation of that diffusion velocity. |
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