Mechanical Properties Anisotropy of Isothermally Forged and Precipitation Hardened Inconel 718 Disk
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718 is being extensively used in numerous applications such as gas turbine compressor disks,[1–4] extrusion dies[5] and containers,[6] fission and fusion reactors structures,[7] etc., due to excellent mechanical properties at room and/elevated temperatures, good corrosion, and oxidation resistance. Critical components like compressor disks that withstand high cyclic/alternating stress and creep loads are fabricated using this alloy. This requires fine microstructures which are obtained by forging process followed by solution treatment and subsequent two-step aging. In order to obtain the optimized properties, shape, size, morphology, and crystallographic orientation of grains as well as precipitates should be strictly controlled in all sections of the disk. However, forge disks by and large exhibit different properties at different locations (rim, web, and
SHAIK KHAJA and K.K. MEHTA, Scientific Officers, are with the RDAQA (M), c/o Defence Research and Development Organisation, Kanchanbagh, Hyderabad 500 058, India. R. VEERA BABU and A.K. SINGH, Scientists, are with the Defence Metallurgical Research Laboratory, Hyderabad 500 058, India. Contact e-mail: singh_ashok3@ rediffmail.com R. SRI RAMA DEVI, Associate Professor, is with the Department of Metallurgical Engineering, Jawaharlal Nehru Technological University, Hyderabad 500 085, India. Manuscript submitted June 17, 2014. Article published online December 18, 2014 1140—VOLUME 46A, MARCH 2015
bore) and orientations (radial and tangential) due to the presence of microstructural inhomogeneity in the material.[8] Mechanical properties of Inconel 718 have been reported extensively for the wrought products for above-mentioned applications.[8–14] It is clear that a correlation as well as demarcation between monotonic and cyclic behavior with respect to various flow parameters in standard heat treatment condition is vital to optimize the properties of disk material. It becomes even more relevant when anisotropy in mechanical behavior is considered in different locations and orientations of compressor disk. The effect of locations and orientations on uniaxial and cyclic flow parameters of compressor disk is rather lacking for Inconel 718 compressor disks. The present work is thus concerned with the study of monotonic and cyclic stress–strain behavior of Inconel 718 disk at room temperature in isothermally forged and precipitation hardened condition. An attempt has been made to investigate the work-hardening behavior of the alloy at different locations namely, rim, web, and bore along tangential direction. This has also been extended to radial direction sample in web region only.
II.
EXPERIMENTAL PROCEDURE
The forged disk of the Inconel 718 used in the present study was obtained from Gas Turbine Research Establishment (GTRE), Bangalore, India. The analyzed METALLURGICAL AND MATERIALS TRANSACTIONS A
chemical composition of the alloy is given in Table I. The as-received material was in the form of forged disk, solution treated at 1228 K ± 278 K (955 C ± 5 C) followed by air cooli
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