Joining of TiAl to Steel by Diffusion Bonding with Ni/Ti Reactive Multilayers

Abstract

Dissimilar diffusion bonds of TiAl alloy to AISI 310 stainless steel using Ni/Ti reactive multilayers were studied in this investigation. The Ni and Ti alternating layers were deposited by d.c. magnetron sputtering onto the base materials, with a bilayer thickness of 30 and 60 nm. Joining experiments were performed at 700 and 800˝C for 60 min under pressures of 50 and 10 MPa. The effectiveness of using Ni/Ti multilayers to improve the bonding process was assessed by microstructural characterization of the interface and by mechanical tests. Diffusion bonded joints were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED), high resolution TEM (HRTEM) and Fast Fourier transform (FFT). The bonding interfaces are thin (approximately 5 µm thick) with a layered microstructure. For all joints, the interface is mainly composed of equiaxed grains of NiTi and NiTi 2 . The thickness and number of layers depends on the joining conditions and bilayer thickness of the multilayers. Mechanical characterization of the joints was performed by nanoindentation and shear tests. Young´s modulus distribution maps highlight the phase differences across the joint´s interface. The highest shear strength value is obtained for the joint produced at 800˝C for 60 min under a pressure of 10 MPa using Ni/Ti multilayers with 30 nm of bilayer thickness.

Microstructural Characterization of Dissimilar Titanium Alloys Joints Using Ni/Al Nanolayers

“…Reactive multilayer thin films are an alternative interlayer for reducing the temperature and/or the pressure needed for diffusion bonding. These multilayers can improve the diffusivity, due to their nanocrystalline nature and high density of defects, and simultaneously act as a local heat source, as the result of the heat released by the exothermic reaction of the multilayers to form intermetallic compounds [15][16][17][18][19][20]. Previous studies [15][16][17] have shown that Ni/Al multilayers are effective in the diffusion bonding of TiAl to themselves [15], to steel [16] and to Ni-based superalloys [17].…”

Impacts of layout, surface condition and alloying elements on diffusion welding of micro process devices

“…For cleaning, sonicating in surfactant solutions and rinsing with acetone or isopropanol are employed [6].…”

Recent Progress in the Joining of Titanium Alloys to Ceramics

“…Promising studies have revealed that reactive multilayers are an auspicious interlayer for bonding similar and dissimilar titanium alloys. Particularly, Ni/Al and Ni/Ti multilayers provide a unique opportunity to drastically improve conventional bonding technologies by acting as local heat sources and enhancing the diffusivity across the interface [15][16][17][18]. This may be a good approach to apply to diffusion bonding between metals and ceramics in order to produce joints with desirable mechanical properties.…”

“…Conventional titanium alloys are continuously challenged by the operation at temperatures higher than 550 • C due to poor high temperature oxidation resistance and creep properties [2]. Whence, the investigations on the production, characterization, and joining of titanium alloys as titanium aluminides (TiAl), TiNi and Ti6Al4V, have increased during the last decades [5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”