Fadiga e fratura da superliga à base de níquel, Inconel 625, submetida a razão de carga R = -1

Abstract

The fatigue process in materials is the failure mechanism with the presence of cyclic stresses. Surface flaws and stress concentrators may lead to nucleation of cracks during this process. The cracks propagate and cause component fracture after a sufficient number of cycles. This failure mechanism has become increasingly important as soon as the technological progress has enabled the implementation of a larger number of structures subjected to different modes of loading and vibrations such as the equipment used in the pre-salt industry. New materials are being developed especially for this sector and they have to meet some specifications to work on this harsh environments. Examples of materials used under such circumstances are the resistant nickel-based alloys. In this context, this study aims to evaluate the behaviour of the Nickel-based superalloy, Inconel 625, under load with load ratio R equal to -1 as well as its mechanical and microstructural properties. The mechanical, microstructural and morphological characterization of Inconel was analyzed by axial fatigue, tensile, hardness, SEM, Electron Backscatter Diffraction (EBSD), Energy-dispersive X-ray Spectroscopy (EDS) and XRD tests. The results indicated that Inconel 625 is able to associate high mechanical strength and moderate hardness with good ductility. The diffractometry allowed to verify the presence of a matrix phase 𝛾 and carbides of the types 𝐶𝑟23𝐶6 and MC. The development of the S-N curve made it possible to estimate the fatigue strength of the material to be approximately 255 MPa. The fracture surfaces were observed by scanning electron microscopy, in order to investigate the effects produced by fatigue cracks. The presence of beach marks and fatigue striations were observed, they are typical characteristics of the fatigue process.