METALS The effect of grain boundary structure on sensitization behavior in a nickel-based superalloy Sandeep Sahu 1 , Nitin Kumar Sharma 1 , Sanjeev Kumar Patel 1 , K. Mondal 2 , and Shashank Shekhar 1, * 1 Grain Boundary Engineering Lab, Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur, U.P. 208016, India 2 WL113A, Western Lab, Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur, U.P. 208016, India Received: 24 April 2018 Accepted: 12 September 2018 Published online: 20 September 2018 Ó Springer Science+Business Media, LLC, part of Springer Nature 2018 ABSTRACT The present work discusses the evolution of grain boundary structure during thermomechanical processing and its effect on sensitization behavior in a nickel- based superalloy. Alloy 600 was deformed to varied degrees of strain (4–25%) using hot rolling followed by annealing at 1000 °C for 10 min followed by water quenching. Structure of the grain boundary was analyzed with reference to various parameters, such as grain boundary character distribution, twin-related domains, misorientation, and triple junction distribution. Each thermomechan- ically processed sample was heat-treated at 650 °C for 24 h before studying its sensitization behavior. The effect of structure of the grain boundary on sensi- tization was assessed through double loop electrochemical potentiokinetic reactivation test and measured in terms of degree of sensitization (DOS). DOS was found to be in a direct relation with the fraction of random high-angle grain boundaries and their connectivity, while it was inversely related to the fraction of low-R coincidence site lattice boundaries and special triple junctions. Resid- ual strain and the fraction of low-angle grain boundaries were found to be weakly related to DOS. We show that a simple parameter can be used to predict the combined effect of all these factors on sensitization behavior. Introduction Nickel-based Alloy 600 is a critical structural material in heat exchangers and pressurized water reactor steam generator tubing in nuclear power plants, air- craft engines, steam turbines, oil and gas equipment, high-temperature tooling and dies owing to their good mechanical properties and high corrosion resistance [1, 2]. However, these alloys are affected by sensitization, in a manner analogous to austenitic stainless steels [3, 4]. It is known that chromium carbide (mainly Cr 23 C 6 ) precipitates preferentially along the grain boundaries when these alloys are exposed to the higher temperature zone (* 500 to Address correspondence to E-mail: shashank@iitk.ac.in https://doi.org/10.1007/s10853-018-2919-7 J Mater Sci (2019) 54:1797–1818 Metals