Aging Effect on the Microstructure of the Superalloy Inconel 939
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Aging Effect on the Microstructure of the Superalloy Inconel 939 M. A. González1*, D. I. Martínez1, A. Pérez1, A. Garza2. Facultad de Ingeniería Mecánica y Eléctrica (FIME-UANL), Av. Universidad s/n. Ciudad Universitaria, C.P.66451 San Nicolás de los Garza, N.L., México. 2Corporación Mexicana de Investigación en Materiales S.A. de C.V. (COMIMSA), Ciencia y Tecnología No.790, Saltillo 400, C.P. 25295 Saltillo Coah., Mexico. E-mail: [email protected] 1
ABSTRACT In this work were evaluated the microestructural characteristics by Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) of the intermetallic ’ (liquation, coarsening and decomposition) in the Inconel 939 alloy after 40000 hours and 850-900°C aging operation conditions. The alloy was vacuum conventional cast. The results show that the liquation phenomena take place in eutectics - ’ which are present mainly in the core of the dendritic arms and in the coarse films of carbides along the grain boundaries (GB), the ’ particles change their original morphology of ordered cuboids of 320nm to disordered and coarse cuboids of 1.2 m, carbides show a morphology change from the original dispersed particles into a coarse continuous films and particles Chinese script type, this affects adversely the mechanical properties such as creep. The results of this evaluation allow to determine the main microestructural damage mechanisms which experiment some components such as blades at high temperatures in industrial conditions. Keywords: Microstructure, diffusion, second phases, optical metallography, scanning electron microscopy (SEM). INTRODUCTION Actually, the design of materials considering the specific applications has lead to the incursion in the development of new superalloys of higher properties. Talking of specific applications, we can consider the different operation conditions between the aero engines and the land and marine turbines. The land and marine gas turbines use a lower grade fuel, with high sulfur contents and operate for longer periods (up to 100,000 hours), and relative lower stress and temperatures than those of the aero engines [1-2]. Such long service periods can be reached if the alloy has good microstructural stability. The base Nickel superalloys, are widely used in the fabrication of each land-base and marine gas power generation turbine blades, their high mechanical properties at elevated temperatures are attributed directly to the precipitation of some phases in the solid state during the fabrication, the ordered intermetallic ’-Ni3(Al,Ti) consider as a first reaction phase and in minor quantity but not les important MC and M23C6 carbides which precipitate in the grain limits [3]. During service the blades of the gas turbines, suffer severe conditions of high temperature and stress, this can lead to some microstructural changes and consequently to the decrease of the mechanical properties such as tensile, creep and fatigue resistance [1-7]. Studies of this superalloys grades has showed that long exposure times to the conditions men
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