High temperature cyclic oxidation of Ni based superalloys at different temperatures in air D. Saber a, * , Islam S. Emam a , R. Abdel-Karim b a Materials Engineering Department, Zagazig University, Zagazig, 44519, Egypt b Petroleum and Metallurgy Dept. Cairo University, Cairo, Egypt article info Article history: Received 13 February 2017 Received in revised form 27 April 2017 Accepted 13 May 2017 Available online 15 May 2017 Keywords: Cyclic oxidation Inconel 617 Superalloy Oxide layer abstract In present study high temperature cyclic oxidation behavior of Ni-based superalloy (Inconel 617) was investigated. The cyclic oxidation test was carried out at various temperatures 750  C, 850  C, 950  C and 1000  C under cyclic conditions in the air for 96 h. Weight gain is measured discontinuously at different oxidation temperatures and times. Weight gain was used to determine the kinetics of oxidation. The oxidation kinetics of the alloys followed a parabolic rate law at 850  C, 950  C and 1000  C. Field emission scanning electron microscopy/energy dispersive spectroscopic analysis (FESEM/EDAX) technique was used to analyze the oxidation products. X-Ray Diffraction (XRD) was used to analyze the formed scale. The protective oxides of Cr 2 O 3 , NiO, and NiCr 2 O 4 were formed, which contributed to the better oxidation resistance. These oxide scales increased with time and temperature and they are compact, dense, distributed uniformly and adherent to the surface of Inconel 617 alloy. © 2017 Published by Elsevier B.V. 1. Introduction Ni-based superalloys are commonly used in the manufacture of aerofoil components such as blades and nozzle guide vanes that work in the hot sections of advanced gas turbine engines [1,2], due to their good high temperature mechanical properties. These su- peralloys do not own adequate oxidation resistance in their service environment, especially in damaged areas where the bare metal is exposed to the oxygen-containing atmosphere. Continual oxidation of the moving crack tip can speed up the crack propagation through the component, causing in shorter service life, mainly under ther- mal cycling conditions. Therefore, high oxidation is a main reason for the failure of hot-section turbine blades [3]. The superalloys have been developed to achieve oxidation resistance by utilizing the concept of selective oxidation. The selective oxidation processes are affected by a number of factors such as alloy composition, surface conditions, gas environment and cracking behavior of the oxide scale [4]. When a clean component is exposed to an oxygen rich gas, small impinging nuclei of all the thermodynamically stable oxides develop on the surface and coalesce rapidly to give a com- plete layer. During the initial or transient stage, the rate of oxidation is rapid, all the elements in the alloy oxidize and the amounts of various oxides in the layer are approximately proportional to the concentration of the elements in the alloy [5,6]. High temperature oxidation involves the oxidation of reactive elements, formation of oxide scales, and internal oxidation [7]. The knowledge of reaction kinetics and the nature of the surface scales formed through high temperature oxidation is important for evaluating the alloys for their use in high-temperature applications. Alloy 617 is considered the greatest favorable structural material because of its high tem- perature strength and oxidation resistance [8]. Several studies have been conducted for Alloy 617 to investigate the high temperature oxidation behaviors in different environments [9e16]. In those studies, the external Cr 2 O 3 layer and the internal Al 2 O 3 oxides were developed in all testing conditions due primarily to the high Cr (22 wt.%) and low Al (1.5 wt.%) contents of Alloy 617 [10e14]. In addition the oxidation resistance and the stability of the surface oxide layer depend on the interplay between temperatures, alloy composition, thermal cycling and oxidizing environment. On the other hand, it is difficult to clarify the oxidation mechanisms of alloy 617 due to its complex chemical composition [12e16]. Degradation by oxidation is one of the main failure modes of hot section components in gas turbines, so an understanding of the oxidation resistance is very necessary for superalloys [17]. In the present investigation, the oxidation behavior of Ni-based superal- loy (Inconel 617) has been studied various temperatures under * Corresponding author. E-mail address: daliasaber13@yahoo.com (D. Saber). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom http://dx.doi.org/10.1016/j.jallcom.2017.05.130 0925-8388/© 2017 Published by Elsevier B.V. Journal of Alloys and Compounds 719 (2017) 133e141