Elsevier

Surfaces and Interfaces

Volume 21, December 2020, 100738
Surfaces and Interfaces

Facilitating low-temperature diffusion bonding between oxygen-free Al2O3 ceramic and pure Cu through inclusion of 0.8 La (wt.%) to Ti pre-metallized interlayer: Microstructural evolution, metallurgical reactions, and mechanical properties

https://doi.org/10.1016/j.surfin.2020.100738Get rights and content

Abstract

The primary objective in this work was to characterize the microstructure, metallurgical reactions, and mechanical properties of joints between oxygen-free Al2O3 ceramic and pure Cu substrates following diffusion bonding at temperatures of 250, 300, or 350°C using a metallization interlayer of Ti-0.8La (wt.%). Diffusion bonding of oxygen-free Al2O3 ceramic and pure Cu substrates was performed using vacuum hot-press diffusion. The joints to be bonded were prepared by applying a pre-metallization interlayer of Ti-0.8La (wt.%). Experiment results demonstrated the successful diffusion bonding of oxygen-free Al2O3 ceramic and pure Cu substrates at temperatures of 350°C. During the process of bonding, the Ti and La diffused toward the Al2O3 substrate to produce a homogeneous diffusion zone with no defects (i.e., cracking or porosity) at the interface. Adding a small quantity of La significantly increased the hardness of the joints as a function of bonding temperature. No indentation cracking was observed at the interface. At an elevated bonding temperature, the inclusion of La reduced the activation energy required for element diffusion, thereby increasing bonding strength in the interfacial diffusion zone and improving the ductility of Al2O3.

Introduction

Aluminum oxide (Al2O3) ceramic and Al2O3-based ceramic composites are widely used as structural materials in nuclear reactors and aerospace, due to their excellent mechanical properties at high temperatures, satisfactory resistance to radiation, and good oxidation and corrosion resistance [1]. However, the high hardness and low fracture toughness of Al2O3 ceramics makes it difficult to machine Al2O3 components and join them to other metallic materials. Heterogeneous bonding (i.e., active metal bonding or diffusion bonding) has attracted considerable attention in industry for the attachment of Al2O3 ceramic to itself or to metals [2,3]. Note that ceramic surfaces require pre-metallization [4], [5], [6], [7], which generally involves the highly-complex and expensive process of Ni plating [8,9]. Numerous bonding methods have been developed, including solid state diffusion bonding, partial transient liquid phase bonding, and active metal brazing [10], [11], [12], [13], [14], [15], [16]. Note that the mechanical properties of the ceramic components depend heavily on the constituents of the active filler material.

The use of active filler materials is particularly well-suited to industrial applications, due to its simplicity and applicability to joints of various shapes and sizes. The soundness of the joints depends primarily on the chemical reactions between the ceramic surface and active elements in the filler material. The most common elements are Ti, Zr, and Hf, which have proven particularly effective in adjusting the wetting and adhesion characteristics of Al2O3 ceramic surfaces following in-situ chemical reactions [17], [18], [19], [20], [21]. Note that these interfacial reactions (particularly those involving Ti) are highly controllable [22]. Researchers have also been working to improve the properties of joints through the addition of a soft interlayer or the in-situ formation of particles or whiskers with a low coefficient of thermal expansion (CTE) [23], [24], [25]. Unfortunately, ceramic joints based on active metallic fillers are unable to withstand high-temperature fabrication techniques, due largely to the fragility of the reaction layers of Ti-Cu-O compounds and Ti oxides on the surface of the Al2O3 ceramic [26], [27], [28], [29]. This has severely limited the applicability of Al2O3 ceramics and necessitated the development of low-temperature active filler metals to facilitate the bonding of ceramics to metals. Ti, Zr, and Hf-based active filler materials have been shown to suppress oxide formation, whereas cerium (Ce) [30,31] and lanthanum (La) [32,33] have been shown to enhance atomic substitution at interfaces. Overall, the high oxygen affinity of such elements reduces the formation of oxides and intermetallic compounds to improve bonding strength.

In the current study, we employed low-temperature (250, 300 and 350°C) hot press diffusion to create bonds between oxygen-free Al2O3 ceramic substrates and pure Cu substrates using a thin layer of Ti-0.8La (wt.%) as a pre-metallization layer. The proposed scheme includes two simple steps: 1) active metallization of the Al2O3 ceramic surface using Ti-0.8La (wt.%) as a composite filler and 2) diffusion brazing of a metallized oxygen-free Al2O3 ceramic substrate and pure Cu substrates at 250, 300, and 350°C. A wide range of experiments were performed to assess the feasibility of the proposed low-temperature diffusion bonding method. The primary function of the experiments was to compare the metallurgical reactions, microstructural evolution, and properties of joints produced under a range of bonding temperatures. The overall objective in this study was to determine whether the inclusion of La in the solder could be used to reduce the temperature of diffusion bonding between Al2O3 and Cu substrates.

Section snippets

Materials, diffusion bonding process, and joint characterization

Success in the diffusion bonding of joints depends on a combination of factors, the most important of which is the preparation of material surfaces, as this determines the initial contact area between diffusion couples. Thus, the diffusion bonding experiments in this study began with the preparation of materials to be joined: 1) Oxygen-free Al2O3 ceramic substrates and pure Cu substrates (10 × 10 × 0.5 mm) were sequentially washed in acetone, isopropanol, and ethanol to remove contaminants, and

Microstructure at interfacial of Al2O3 ceramic and Cu substrates

Fig. 2(a)~(c) present backscattered electron images (BEI) of Al2O3 / Cu diffusion-bonded joints respectively processed at temperatures of 250, 300, and 350°C. Fig. 3(a)~(c) present corresponding line scans of the constituent elements in each joint. The line scan results confirm that the Ti-0.8La (wt.%) interlayer facilitated the solid-state diffusion bonding of the Al2O3 ceramic substrate to the Cu substrate via and the formation of a 150~250 nm diffusion bonding zone (i.e., reaction zone). As

Conclusions

This study investigated the low-temperature diffusion bonding of metal and ceramic substrates using a Ti-0.8La (wt.%) pre-metallization layer. Experiment results support the following conclusions:

  • (1)

    Bonding at temperatures of 250, 300, and 350°C was shown to facilitate the formation of strong diffusion bonds between Al2O3 and the Cu substrate. The strong diffusion of La and Ti toward the Al2O3 substrate can be attributed to the strong affinity of La for oxygen and the ease with which Al is

Authors' contribution

Dr. Chun-Ming Lin conceived the experimental design, analyzed the results, and reviewed and edited the manuscript. In addition, Miss Tseng-Pei-Hsins conducted the experiments, prepared the draft manuscript, including both the text and the figures and tables.

Declaration of Competing Interest

This manuscript has not been published or presented elsewhere in part or in entirety, and is not under consideration by another journal. All authors have approved the manuscript and agreed with submission to your esteemed journal. There are no conflicts of interest to declare.

Acknowledgements

The authors would like to thank the Ministry of Science and Technology of Taiwan for the financial support of this study under Contract no. MOST 105-2218-E-027 -011-MY3. Finally, the authors are grateful to Miss Tseng-Pei-Hsins for his assistance in publishing this work.

References (50)

  • D. Travessa et al.

    Diffusion bonding of aluminum oxide to stainless steel using stress relief interlayers

    Mater. Sci. Eng. A

    (2002)
  • Y.X. Zhao et al.

    Brazing TC4 alloy to Si3N4 ceramic using nano-Si3N4 reinforced AgCu composite filler

    Mater. Des.

    (2015)
  • C.Y. Ma et al.

    Influence of alumina bubble particles on microstructure and mechanical strength in porous Cu-Sn-Ti metals

    Mater. Des.

    (2015)
  • O. Kozlova et al.

    Initial stages of wetting of alumina by reactive CuAgTi alloys

    Scr. Mater.

    (2011)
  • R. Voytovych et al.

    The relation between wetting and interfacial chemistry in the CuAgTi/alumina system

    Acta Mater.

    (2006)
  • S. Mandal et al.

    Correlation between the mechanical properties and the microstructural behavior of Al2O3-(Ag-Cu-Ti) brazed joints

    Mater. Sci. Eng. A

    (2004)
  • Z.W. Yang et al.

    Interlayer design to control interfacial microstructure and improve mechanical properties of active brazed Invar/SiO2-BN joint

    Mater. Sci. Eng. A

    (2013)
  • Z.W. Yang et al.

    Interfacial microstructure and mechanical properties of TiAl and C/SiC joint brazed with TiH2-Ni-B brazing powder

    Mater. Charact.

    (2013)
  • T.S. Lin et al.

    Effect of in situ synthesized TiB whisker on microstructure and mechanical properties of carbon-carbon composite and TiBw/Ti-6Al-4V composite joint

    Mater. Des.

    (2011)
  • R. Pan et al.

    Effects of electric field on interfacial microstructure and shear strength of diffusion bonded α-Al2O3/Ti joints

    J. Eur. Ceram. Soc.

    (2015)
  • J. Cao et al.

    Processing, microstructure and mechanical properties of vacuum-brazed Al2O3/Ti6Al4V joints

    Mater. Sci. Eng. A

    (2012)
  • O. Kozlova et al.

    Brazing copper to alumina using reactive CuAgTi alloys

    Acta Mater.

    (2010)
  • G.T. Yin et al.

    Effect of interlayer thickness on the microstructure and strength of WC-Co/Invar/316L steel joints prepared by fibre laser welding

    J. Mater. Process. Technol.

    (2018)
  • C. Ma et al.

    Study on novel Ag-Cu-Zn-Sn brazing filler metal bearing Ga

    J. Alloys Compd.

    (2016)
  • H.W. Jiang et al.

    Influence of cooling rate and addition of lanthanum and cerium on formation of nanoporous copper by chemical dallying of Cu15Al85 alloy

    J. Rare Earths

    (2013)
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