Joining Ti6Al4V to Alumina by Diffusion Bonding Using Titanium Interlayers

Abstract

This work aims to investigate the joining of Ti6Al4V alloy to alumina by diffusion bonding using titanium interlayers: thin films (1 µm) and commercial titanium foils (5 µm). The Ti thin films were deposited by magnetron sputtering onto alumina. The joints were processed at 900, 950, and 1000 °C, dwell time of 10 and 60 min, under contact pressure. Experiments without interlayer were performed for comparison purposes. Microstructural characterization of the interfaces was conducted by optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD). The mechanical characterization of the joints was performed by nanoindentation to obtain hardness and reduced Young’s modulus distribution maps and shear strength tests. Joints processed without interlayer have only been achieved at 1000 °C. Conversely, joints processed using Ti thin films as interlayer showed promising results at temperatures of 950 °C for 60 min and 1000 °C for 10 and 60 min, under low pressure. The Ti adhesion to the alumina is a critical aspect of the diffusion bonding process and the joints produced with Ti freestanding foils were unsuccessful. The nanoindentation results revealed that the interfaces show hardness and reduced Young modulus, which reflect the observed microstructure. The average shear strength values are similar for all joints tested (52 ± 14 MPa for the joint processed without interlayer and 49 ± 25 MPa for the joint processed with interlayer), which confirms that the use of the Ti thin film improves the diffusion bonding of the Ti6Al4V alloy to alumina, enabling a decrease in the joining temperature and time.

Joining of Ti6Al4V to Al2O3 Using Nanomultilayers

“…These periods were selected based on the reactivity of Ni/Ti multilayers and on previous dissimilar joining of metallic materials by diffusion bonding [31,34]. A deposition time of ~30 min was selected for a total thickness close to 2.5-3.0 µ m. Titanium's bottom nanolayer ensured a good adhesion to the base materials [24]. Adhesion between Ni/Ti thin films and substrate is particularly relevant for the Al2O3 base material because the lack of adhesion can compromise the diffusion bonding process.…”

“…However, the conventional diffusion bonding process involves high temperature, pressure, and dwell time which causes thermal stress due to a mismatch in coefficient of thermal expansion (CTE) and thermal conductivity; consequently, cracks come up at the joint's interface, mainly during cooling [1]. Thus, several approaches have been developed to join dissimilar materials by diffusion bonding, like applying interlayers between the base materials to be joined [17][18][19][20][21][22][23][24]. The interlayer has a crucial role in reducing the temperature and pressure of the bonding process, and consequently, the thermal stress, besides increasing the contact area that favors achieving high strength joints.…”

Microstructure and Mechanical Properties of Ti6Al4V to Al2O3 Brazed Joints Using Ti-Ag/Cu-Ti Thin Films

“…Solid-state diffusion bonding is one of the most common joining processes reported in the literature when creating joints between titanium alloys and advanced ceramic materials. However, in these studies it is observed that achieving joint integrity is only possible with high pressures at elevated temperatures [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. The drawbacks of this process are primarily associated with economic concerns, due not only to the required equipment but also the processing of the joints and preparation of the base materials.…”

“…The use of thin films or multilayers as an interlayer has been demonstrated as a viable approach in bonding Ti6Al4V to Al 2 O 3 through diffusion bonding [9][10][11][12]. This application is attributed to the potential for enhancing diffusivity across the interface, thereby reducing processing conditions, decreasing residual stresses, and improving joint integrity.…”

Impact Joining of Pure Copper C1100 and Aluminum Alloy A6061-T6 Plates at Edges

“…The surface exposure and the pressure affect the welding strength [11]. Diffusion bonding was also tested at high temperatures [12][13][14]. Severe plastic deformation breaks the thin brittle oxide surface layer to press the newly created surface under high pressure.…”