Microstructure and Mechanical Properties of Ti-6Al-4V Alloy/Interstitial Free Steel Joint Diffusion Bonded with Applicat
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TANIUM (Ti) and its alloys are used in several industries such as aerospace, biomedical, nuclear and chemical as well as for sports applications, which demand high specific strength and very good fatigue, creep and corrosion resistance. In some situations, to cater to the specific surface and functional requirements in service or to lower the material utilization costs, the Ti alloys are usually joined with steels of various types.[1,2] However, due to significant differences in physical and chemical properties, the conventional fusion welding is not preferred for these materials. This is primarily because the Ti alloys are reactive in nature at high fusion temperature, and joining with steel results in segregation and formation Fe-Ti brittle phases (due to limited solubility of Fe in Ti) and large residual
MANIL RAJ, M.J.N.V. PRASAD, and K. NARASIMHAN are with the Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400 076, India. Contact e-mail: [email protected] Manuscript submitted February 21, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
stresses in the joint zone, thereby causing premature failure of the joints.[3,4] To overcome these problems, the solid-state diffusion bonding method is the most preferred for joining this category of dissimilar materials.[5,6] In diffusion bonding, coalescence is achieved between two materials (both similar and dissimilar) by means of atomic diffusion, under the combined application of pressure and temperature (0.5 to 0.7 Tm) for a certain duration in vacuum or an inert environment.[7] In this joining technique, apart from direct bonding, the interfacial materials or interlayer/s in the form of foils, coatings, films and powders are incorporated at the bonding interface to achieve coalescence at lower values of bonding parameters. The interlayers also assist in minimizing the metallurgical incompatibility by reducing the formation of brittle intermetallics. The interlayer materials are selected based on their feasibility for production of joints, with the predefined joining parameters and depending on the physicochemical and mechanical properties of the joints desired in the service conditions.[8] In the case of dissimilar joints of Ti alloys with steels, the ductile materials such as copper, nickel, aluminum, silver, etc., are considered potential
interlayers. Sometimes, a combination of these materials (alloys or multi-interlayer) is also preferred.[9,10] There is extensive literature available for solid-state diffusion bonding of Ti alloys and stainless steels (SS) by direct bonding as well as with interlayers. Ghosh and Chatterjee[5] performed diffusion bonding between commercially pure titanium and 304 SS. They reported an increase in the concentration of intermetallic phases at the interface with the increase in bonding temperature. In addition to TiFe and TiFe2, k and r phases were also detected because of enriched chromium content in the bonding zone. A maximum joint strength of ~ 235 MPa was reported for the b
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