Mechanical Properties and the Microstructure of Al2O3/Al/Al2O3 Joints with the Surface Modification of Alumina by a Thin Layer of Ti + Nb

Marzanna Książek ,Adam Tchórz ,Łukasz Boroń

doi:10.1007/s11665-014-0980-1

Abstract

Al2O3/Al/Al2O3 joints were formed by liquid-state bonding of alumina substrates covered with a thin Ti + Nb coating of 900 nm thickness with the use of an Al interlayer of 30 μm at 973 K under a vacuum of 0.2 mPa for 5 min. The bond strength of the joints was examined by a four-point bending test at 295, 373, and 473 K. Optical, scanning, and transmission electron microscopies were applied for detailed characterization of the interface structure and failure characteristics of fractured joint surfaces. The analysis of the results has shown that (i) bonding occurred due to the formation of a reactive interface on the metal side of the joint in the presence of Al3Nb(Ti) precipitates and (ii) modification of Al2O3 by a thin layer of Ti + Nb increases the hardness at the interface and makes it possible to achieve reliable joints working at elevated temperatures.

Highlights

The metal/ceramic joint showed a series of unique properties that do not occur in any other material in such a combination
Maximum bending stress at T = 473 K decreases twofold, while Al2O3/Ti + Nb/Al/Ti + Nb/Al2O3 joints in the tested temperature range maintain the same character of the bending curve, which in turn proves the same character of the deformation mechanism at the room temperature and elevated temperature
It has been shown that the bending strengths of metal-ceramic joints with Ti + Nb coating have been improved compared to those joints without coatings at elevated temperature

Summary

Introduction

The metal/ceramic joint showed a series of unique properties that do not occur in any other material in such a combination. The applicability and occupied time of the final metal/ceramic joints depend on the dissipation of the stress concentration, which increases the ceramicÕs cracking strength in the formation of such interatomic bonds that will ensure obtaining a durable and reliable joint. The reactivity and wetting behavior in a metal/ceramic system can in turn be improved, e.g., by applying thin metallic layers to the ceramic material surface (Ref [5, 6]) Such layers can be reactive against the bonded materials so that a fixed bond on the phase boundaries is formed, creating diffusion, reactive intermediate microlayers in the most favorable case; the layers have a physical and chemical compatibility (thermodynamic and kinetic), which guarantees good mechanical characteristics of the joint. Kelkar et al in their study (Ref 7) on the basis of thermodynamic calculations present a concept that the influence between liquid Al and titanium covering Al2O3 in a vacuum, even at low partial pressures of oxygen, leads to changes in the chemical composition of the interface at the side of the substrate by forming the following reaction layer: Al/Al2O3/TixOy/Ti/TixOy/Al2O3

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Conclusion