Effect of Ti, Nb, and Ti + Nb Coatings on the Bond Strength-Structure Relationship in Al/Al 2 O 3 Joints Marzanna Ksiazek, Maria Richert, Aam Tchorz, and Lukasz Boron (Submitted August 24, 2011; in revised form November 21, 2011) There is a growing interest in metal-ceramic bonding for wide range of applications in electronic devices and high technology industry for fabrication of metal matrix composites and bonding of ceramic compo- nents to metals. The object of the work was to study the effect of Ti, Nb, and Ti + Nb thin films deposited by PVD method on alumina substrates on structure and bond strength properties of Al/Al 2 O 3 joints. The joints were fabricated using the results of a wetting experiment and the sessile drop method at a temperature of 1223 K in a vacuum of 0.2 MPa for 30 min of contact. The structure of the metal/ceramic interface was investigated using scanning electron microscopy. The elemental distribution at the metal-ceramic interface was analyzed using energy dispersive x-ray spectroscopy. Transmission electron microscopy was also used to investigate some aspects of the metal/ceramic interface. The bond strength properties of joints were measured using shear test. The shear strength results demonstrated significant improvement of shear strength of Al/Al 2 O 3 joints due to the application of Ti + Nb thin film on alumina substrate. Microstruc- tural investigations of the interface indicated that Al/coating/Al 2 O 3 couples have diffusion transition interface which influences the strengthening of these joints. A conclusion could be drawn that the presence of thin film layers changes the character of interaction and leads to the formation of new reaction products in the bonding layer. Keywords coatings, joining, surface engineering 1. Introduction The growing popularity of technical solutions that offer metal-ceramic joints is mainly due to the fact that we obtain a combination of materials characterized by different structures and physico-chemical properties. Therefore metal-ceramic joints are widely used by different sectors of industry as both functional and structural materials (Ref 1). When bonding together alumina and metals, the main problem is to ensure reliable joints. It is well known that in the liquid phase technology of metal-ceramic joint fabrication, applying the deposition of thin metallic films on ceramic surface can improve wetting, interface structure, and bonding strength properties of metal-alumina joints (Ref 2-4). The increase of bond strength is due to hardening of metal-ceramic interface through formation of intermediate diffusion-type layers. Yet, we should remember that a strong and fast bond between the metal and the ceramic material can be produced only when the system has proper wettability, i.e., the ability to coat the surface of ceramics with a continuous film of metal. This is possible, on one hand, through control of the temperature- and time-related parameters of the bonding process and, on the other, through optimizing of this process by metallization of the ceramic material surface. The purpose of this work was to study the effect of Ti, Nb, and Ti + Nb thin film on alumina on the bond strength properties and interface structure in Al/Al 2 O 3 joints. 2. Experimental Procedure and Materials The following materials were used in the investigations: aluminum (99.9999 wt.%) and polycrystalline alumina acting as a substrate, fabricated at the Faculty of Materials Science and Ceramics, University of Science and Technology in Kracow. The polycrystalline alumina substrates were prepared from powders of the following starting composition: 99.9085% a-Al 2 O 3 , 0.009% CaO, 0.053% SiO 2 , 0.0029% MgO, 0.023% Fe 2 O 3 , and 0.0036% Na 2 O. Blocks ([17 9 25 mm) were produced by casting in molds under pressure (200 MPa) and sintered at the temperature 1923 K for 2 h. Substrates ([17 9 5 mm) were cut from sintered blocks using a diamond saw. The alumina substrate was characterized by the following physical and mechanical properties: porosity—almost 0%, density—3.8 g/cm 3 , YoungÕs modulus—300 GPa, Poisson ratio—0.24. To produce a bond between the ceramic substrate and the metal, a wettability experiment was carried out by the sessile drop method. The wettability experiment was carried out at the temperature of 1223 K for of 30 min in dynamic vacuum of This article is an invited submission to JMEP selected from presentations at the Symposia ‘‘Wetting, soldering and brazing’’ and ‘‘Diffusion bonding and characterization’’ belonging to the Topic ‘‘Joining’’ at the European Congress and Exhibition on Advanced Materials and Processes (EUROMAT 2011), held September 12-15, 2011, in Montpellier, France, and has been expanded from the original presentation. Marzanna Ksiazek, Aam Tchorz, and Lukasz Boron, Complex of Research Laboratories, Foundry Research Institute, 73 Zakopianska St., 30-418 Krakow, Poland; and Maria Richert, University of Science and Technology, 30 Mickiewicza Ave., 30-059 Krakow, Poland. Contact e-mail: marzena@iod.krakow.pl. JMEPEG (2012) 21:690–695 ÓASM International DOI: 10.1007/s11665-012-0120-8 1059-9495/$19.00 690—Volume 21(5) May 2012 Journal of Materials Engineering and Performance