Improvement in Laser Weldability of INCONEL 738 Superalloy through Microstructural Modification
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INTRODUCTION 738, like many other nickel-base
*INCONEL and IN are trademarks of INCO Alloys International, Huntington, WV.
superalloys, offers a wide range of properties that allows its use under stringent service conditions, such as in land-based and aero gas turbine engines. Among its most notable properties are the following: excellent high-temperature strength, hot corrosion resistance, oxidation, and sulfidation resistance. The high-temperature strength, derived from the precipitation of the ordered L12 intermetallic Ni3(Al,Ti) c¢ phase within a c matrix, allows it to be used at temperatures up to 980 C. Requirements for improved turbine efficiency in both aero-engines and power applications, which involves increasing the turbine inlet temperature, have necessitated that the alloy be used under increasingly more stringent stress and temperature conditions, resulting in a more rapid degradation of components in A.T. EGBEWANDE, Graduate Student, formerly with the Department of Mechanical and Manufacturing Engineering, University of Manitoba, is with the Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, Canada, T6G 2V4. H.R. ZHANG, Postdoctoral Research Fellow, R.K. SIDHU, Electron Microprobe and SEM Manager, and O.A. OJO, Associate Professor, are with the Department of Mechanical and Manufacturing Engineering, University of Manitoba, Winnipeg, MB, Canada, R3T 5V6. Contact e-mail: [email protected] Manuscript submitted October 1, 2008. Article published online September 1, 2009 2694—VOLUME 40A, NOVEMBER 2009
service.[1] This necessitates that damaged components be either replaced or repaired. However, the cost of producing new components is exorbitant, and economic considerations usually favor the repair of damaged components. Also, in today’s highly competitive and profit driven manufacturing industry, the ability of a company to supply its products at the lowest cost possible without compromising product quality and safety can be an important edge over competitors. Thus, whether for the purposes of fabrication of new components or repairs of service damaged ones, it is important that industries employ the most efficient processes that reduce both the throughput price and production times. For these reasons, industries often employ some forms of welding during the fabrication or repairs of engineering components. Laser welding is a relatively new fusion welding technique that offers several advantages over conventional welding methods used in the joining of nickel-base superalloys. These advantages include rapid production through the use of higher welding speed, lower installation and running costs, smaller floor space requirement, flexibility of use, and ability to weld complex structures by delivering lasers to remote parts with fiber optics and reduced heat input, which reduces the heataffected zone (HAZ) size.[2–6] However, the application of fusion welding processes to precipitation-hardened nickel-base superalloys containing high Al + Ti content such as IN 738 has been severe
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