A Study on the Effect of Process Parameters on the Properties of Joint in TLP-Bonded Inconel 738LC Superalloy
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TION
IN-738LC is a polycrystalline nickel-based superalloy widely used in the aerospace and power generation industries because of its superior mechanical properties and corrosion and oxidation resistance at elevated temperatures. The exceptional high-temperature strength of IN-738LC is related to the presence of L12type ordered Ni3(Al,Ti) c¢ intermetallic fcc phase in the c solid solution matrix.[1] However, a high volume fraction of c¢ (40 to 43 vol. pct) in the IN-738LC[2] improves the elevated mechanical properties of this superalloy, but c¢ reduces weldability of IN-738LC significantly.[3] Brazed joints have also been found to be plagued by the formation of hard and brittle eutectic microconstituents during the joining.[4,5] Transient liquid phase (TLP) bonding which combines the beneficial features of the liquid phase joining and diffusion bonding techniques has been developed as an attractive alternative method for joining and repairing non-weldable superalloys.[6–14] In TLP bonding, a filler metal containing melting point depressant (MPD)
elements is sandwiched between the substrate layers. Then, the whole assembly is heated up to a temperature between the liquidus of the filler metal and that of the base alloy. Generally, it is considered that four distinct stages are present during the TLP-bonding process, namely dissolution of the base alloy, widening of the interlayer, isothermal solidification of the liquid, and homogenization of the bond region. If the bonding time is not sufficient to complete the isothermal solidification, formation of eutectic constituents could occur along the joint. These constituents are detrimental to the mechanical properties of the joints.[12,15] A proper selection of various process parameters is therefore an important issue for achieving reliable TLP-bonded joints in IN738LC. It was therefore the goal of the present study to investigate the effect of gap size, bonding temperature, and time on the microstructure and properties of TLPbonded IN-738LC superalloy using AMS 4777 filler alloy, and the results are reported and discussed in this paper. II.
V. JALILVAND, MSc Graduate, and H. OMIDVAR, Assistant Professor, are with the Department of Mining and Metallurgical Engineering, Amirkabir University of Technology (Tehran Polytechnic), 15875-4413 Tehran, Iran. Contact e-mail: [email protected] H.R. SHAKERI, Senior Visiting Scientist, is with the Department of Materials Science and Engineering, University of Toronto, Toronto, ON M5S 3E4, Canada. M. R. RAHIMIPOUR, Associate Professor, is with the Department of Ceramic, Materials and Energy Research Center, 31787-316 Karaj, Iran Manuscript submitted January 15, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
EXPERIMENTAL PROCEDURES
A. Materials The base material used in the present study was cast polycrystalline IN-738LC superalloy with chemical composition as given in Table I. Specimens with the size of 10 9 10 9 5 mm were cut from the as-received base alloy using a wire electro-discharge machine. TLP bonding was carried out using powd
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