Diffusion Bonding of Microduplex Stainless Steel and Ti Alloy with and without Interlayer: Interface Microstructure and
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INTRODUCTION
IN the recent years, titanium/titanium alloy and stainless steel joints have been used in space, chemical, and nuclear industries.[1–4] Titanium/titanium alloy has excellent corrosion resistance and high specific strength and finds potential applications in processing units.[3,4] It is very often required to join with the stainless steel to fabricate a single component in one structure. The conventional fusion welding of these materials can result in segregation of chemical species, stress concentrations, and formation of brittle intermetallics at the bond interface, which ultimately results in crevice corrosion or fatigue failure during service.[5–10] In diffusion bonding for producing a metallurgical joint between dissimilar metals, a higher bonding temperature and longer bondS. KUNDU, Assistant Professor, S. SAM, Doctoral Student, and S. CHATTERJEE, Professor, Director of Research and Consultancy, are with the Department of Metallurgy and Materials Engineering, Bengal Engineering and Science University, Shibpur, Howrah 711103, West Bengal, India. Contact e-mails: [email protected]; schatterjee@ metal.becs.ac.in B. MISHRA, Professor, is with the Department of Metallurgical and Materials Engineering, Colorado School of Mines, 1500 Illinois St, Golden, CO 80401. Manuscript submitted December 9, 2011. Article published online October 3, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
ing time are needed to increase the interdiffusion rate of relative elements. In this case, the grain growth of parental metals and an increase in the thickness of intermediate phases are difficult to avoid.[2] In addition to this, the thermo-stress as developed in the joints due to the differences in the coefficient of linear expansion between the titanium alloy (TiA) and stainless steel is harmful to both the mechanical properties and corrosion resistance of the joints.[11,12] So, it is very important to join the dissimilar materials at relatively lower bonding temperatures and shorter bonding times using appropriate intermediate materials. The intermediate materials are used for several reasons such as (1) to minimize thermal expansion mismatch, (2) to reduce bonding temperature and/or pressure, (3) to inhibit diffusion of undesired element, and also (4) to reduce or to avoid the formation of brittle intermetallic phases.[13–15] The literature reports that shear strength of ~148 MPa was obtained for diffusion-bonded Ti-6Al-4V and a stainless steel joint when processing was carried out at 1123 K to 1153 K (850 C to 880 C) for 10 to 20 minutes under 10 to 15 MPa load using a 30-lm-thick Ni interlayer.[16] However, direct bonding of these two dissimilar materials results in lower bond shear strength of ~72 MPa.[17] Orhan et al.[18] report that the diffusion bonding of VOLUME 45A, JANUARY 2014—371
microduplex stainless steel (MDSS) and Ti alloy was processed at 1073 K to 1155 K (800 C to 882 C) for 15 and 30 minutes and they also mentioned that good quality bonds were produced at lower bonding temperatures and times. However
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