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Abstract
Ceramic-to-metal heterojunctions have been established to improve high-temperature stability for applications in aerospace and harsh environments. In this work, we employed low-temperature diffusion bonding to realize an alumina/Cu heterogeneous joint. Using a thin layer of lanthanum-doped titanium (La-doped Ti) to metallize the alumina surface, we achieved the bonding at a temperature range of 250–350 °C. We produced a uniform, thermally stable, and high-strength alumina/Cu joint after a hot-press process in vacuum. Signals from X-ray diffraction (XRD) suggested the successful diffusion of Ti and La into the alumina substrate, as Ti can easily substitute Al in alumina, and La has a better oxygen affinity than that of Al. The transmission electron microscopy and XRD results also showed the existence of CuxTiyO phases without CuxTiy or LaOx. In addition, the bonding strength of alumina/copper hot-pressed at 250, 300, and 350 °C were 7.5, 9.8 and 15.0 MPa, respectively. The process developed in this study successfully lowered the bonding temperature for the alumina/copper joint.
Highlights
Heterojunctions of ceramics and metals have received increased attention because of the requirements of high-temperature-resistant composite parts in aerospace or military fields
This study demonstrated that the adhesion strength of the sputtered copper thin film on the alumina substrate was enhanced by their inter-diffusion
The pre-metallization process resulted in the formation of uniform thin films of Ti–0.5La and pure copper, showing a strong inter-diffusion of elements that promoted bonding with the alumina substrate
Summary
Heterojunctions of ceramics and metals have received increased attention because of the requirements of high-temperature-resistant composite parts in aerospace or military fields. There are many welding techniques [1] of ceramics and metals that have been developed from traditional active brazing, which wet the interface by melting active metals [2]. The techniques of active soldering [3,4] and pre-metallization [5,6,7] attracted our attention, because of their low active temperature and good bonding behavior. Direct bonding of copper to alumina has been developed by an eutectic reaction of copper and cuprous oxide at 1050 ◦ C [8]. Sn0.3 Ag0.7 Cu to bond copper and alumina at 620 ◦ C [9]. The predictability and strength have been enhanced, based on low active energy, to form a good junction, suppressed intermetallics [10,11], Coatings 2018, 8, 401; doi:10.3390/coatings8110401 www.mdpi.com/journal/coatings
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