Effect of Bonding Temperature on Phase Transformation of Diffusion-Bonded Joints of Duplex Stainless Steel and Ti-6Al-4V
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the recent years, bonded joints of titanium alloy to conventional structural steel have applications in several industries such as aerospace, chemical, and nuclear;[1–3] however, the welding of dissimilar metals is very difficult due to their differences in thermal, physical, and chemical properties. The diffusion bonding technique is considered as one of the best alternatives of joining of dissimilar metals.[4–6] Nevertheless, the diffusion bonding of Ti and SS without interlayer leads to formation of layer-wise different intermetallics, such as FeTi, Fe2Ti, r, Fe2Ti4O, and TiC due to restricted solubility,[7–10] SUKUMAR KUNDU, Assistant Professor, GOPINATH THIRUNAVUKARASU, Ph.D. Scholar, SUBRATA CHATTERJEE, Professor, are with the Department of Metallurgy and Materials Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah, West Bengal 711103, India. Contact e-mails: [email protected], [email protected] BRAJENDRA MISHRA, Professor, is with the Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, Colorado 80401. Manuscript submitted July 9, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
which are prone to crack, and leads to the formation of micro-cracks at the bonded region under the effect of the residual stresses occurring at the interface due to the difference in coefficient of linear expansion.[11,12] Alema´n et al.[11] reported another factor which is responsible for crack formation during the diffusion bonding, and they found that large internal stresses formed because of differences in the coefficients of linear expansion and thermal conductivities of Fe and Ti elements. The literatures reported that intermediate metals were used in between SS and Ti/Ti-alloy to block the formation of Fe–Ti-based intermetallics and bond strength improved as compared to those direct bonded joints.[13–16] The literature also reported that shear strength of ~148 MPa for diffusion-bonded Ti-6Al-4V and SS joints processed at 1123 K to 1153 K (850 C to 880 C) for 10 to 20 minutes under 10 to 15 MPa load using ~30-lm-thick Ni interlayer.[14] On the contrary, direct bonding of these two dissimilar metals resulted lower bond shear strength of ~72 MPa.[17] Orhan et al.[18] suggested that the formation of Fe–Cr–Ti-based intermetallics resulted in even worse mechanical properties of the diffusion-bonded Ti/Fe
joints. Dey et al.[19] reported that bend ductility of friction stir welding of SS and Ti-alloy was almost zero due to the formation of Fe–Ti-based intermetallics. Gao et al.[20] reported tensile strength of ~221 MPa for the joints of Ti-6Al-4V and 304L SS by laser-beam welding using Mg interlayer. They found Mg17Al12 intermetallic at the Ti-6Al-4V/Mg interface, whereas SS/Mg interface was free from intermetallic. Wang et al.[21] reported that a crack-free electron beam welded joints of Ti6Al2Mo2V2Zr alloy and 304 SS, using Cu filler metal, with the highest tensile strength of ~310 MPa. They reported that the fracture apparently propagates through the Cu–Ti-based int
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