Microstructural evolution and bonding mechanisms of the brazed Ti/ZrO 2 joint using an Ag 68.8 Cu 26.7 Ti 4.5 interlayer
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In this study, 3 mol% Y2O3-stabilized zirconia (3Y–ZrO2) and commercially pure titanium (cp-Ti) joints were fabricated with an Ag68.8Cu26.7Ti4.5 interlayer (Ticusil) at 900 °C for various brazing periods. After brazing at 900 °C/0.1 h, Ti2Cu, TiCu, Ti3Cu4, and TiCu4 layers were present at the Ti/Ticusil interface, while TiCu and TiO layers were observed at the Ticusil/3Y–ZrO2 interface. In the residual interlayer, clumpy TiCu4 was formed along with the Ag solid phase. After brazing at 900 °C/1 h, Ti3Cu3O and Ti2O layers were formed at the interlayer/ZrO2 interface, while Cu2O was precipitated in the residual interlayer with ½111Cu2 O ==½111Ag and ð202ÞCu2 O ==ð202ÞAg . After brazing at 900 °C/6 h, a two-phase (a-Ti 1 Ti2Cu) region was observed on the Ti side with ½2 1 10aTi ==½100Ti2 Cu and ð0002ÞaTi ==ð013ÞTi2 Cu , while the TiCu layer grew at the expense of Ti3Cu4 and TiCu4. The bonding mechanisms and diffusion paths were explored with the aid of Ag–Cu–Ti and Ti–Cu–O ternary phase diagrams.
I. INTRODUCTION
The Ag–Cu eutectic alloy with 28Cu (wt%) is frequently used in the conventional brazing of Ti alloys and other materials at temperatures higher than 800 °C.1 The brazed assembly exhibits good bonding strength, resulting from the formation of Ti–Cu compounds that enhance the wettability of the solid/liquid interface.2,3 However, Sn, Ag, Cu, Ni, Co, and Fe exhibit very poor wettability on the surface of ceramics.4 The wettability can be significantly improved by adding active metals, such as Ti, Zr, and Hf, to the brazing filler. These metals can effectively reduce the interfacial energy by their strong chemical attraction to the oxide ceramic and can enhance the wetting behavior,5 which even enables the surface of the ceramic to be wetted by the formation of the intermediate layer during brazing and provides a good joint.6,7 Hanson et al.7 observed that a small percentage of Ti addition (;4.5Ti wt%) to the braze alloy led to a significant increase in the four-point bend strength of a PSZ–PSZ (PSZ, partially stabilized zirconia) joint. In comparison with PSZ–PSZ or PSZ-stainless steel joints, the 3Y–ZrO2/Ti brazing couple using a Cusil ABA [63Ag–35.25Cu–1.75Ti (wt%)] had a superior joint strength due to the suitable reaction layers at the interface. The microstructural evolution at the interface between the Ti alloy (or ZrO2) and braze alloy has been previously explored based on microstructural characterization using scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS).1–3,6,8 However, the SEM/EDS spatial resolution was limited to a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.30 684
J. Mater. Res., Vol. 29, No. 5, Mar 14, 2014
http://journals.cambridge.org
Downloaded: 24 Apr 2015
the micro range (,2 lm) and unable to analyze the crystal structures. In this study, the braze filler of Ticusil [68.8Ag–26.7Cu–4.5Ti (wt%)] was selected to join the 3Y–ZrO2 and Ti at 900 °C for various brazing periods. The objective was to elucida
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