Abstract
Inconel 625 is a nickel-based highly-resistant superalloy widely used in aerospace components, in the nuclear industry, and especially in the maritime industry. Materials such as Inconel 625 have been widely used in oil exploration of Brazilian pre-salt layers due to their excellent resistance to corrosion under tension, pitting and crevice corrosion by chloride and sulphide ions, and also because they are resistant to microbiological corrosion. All components used in the exploration of crude oil in these environments suffer mechanical fatigue from oceanic oscillations that naturally occur. Samples were precisely machined and tested under uniaxial tension and cyclic tension-compression fatigue following determinations of the ASTM E8M and ASTM E466 standards respectively, at a loading ratio of R = -1. Tensile strengths of 586, 472, 382 and 306 MPa were selected according to the yield strength of the material for raising the S-N curve. A macro and microstructural characterization regarding failure modes was performed revealing that fatigue striations predominated in the stable region of crack growth, whereas microvoids coalescence prevailed in the fast fracture zone. Inconel 625 presented a refined microstructure composed of equiaxial grains with a mean size of 14 µm, typical of refining obtained by hardening followed by recrystallization. The precipitation of MC type carbides (M=Mo or M=Nb) and Cr23C6 dispersed in the austenitic matrix of Inconel 625 controls a secondary alloy hardening mechanism.
Highlights
One of the major engineering challenges today is the development of materials capable of withstanding the most diverse types of mechanical demands in harsh environments
The purpose of this paper is to investigate the fatigue behavior of Inconel 625 in determining its S-N curve - applied stress versus number of cycles - when subjected to a traction-compression cyclic loading at a loading ratio of R = -1
For this analysis will be considered the samples submitted to the three loading levels near the infinite fatigue life region, this loading amplitudes are shown in the table 2
Summary
One of the major engineering challenges today is the development of materials capable of withstanding the most diverse types of mechanical demands in harsh environments. Inconel 625 is an austenitic nickel-based superalloy with cubic crystalline face-centered structure, hardened by solid solution from the addition of chemical elements such as molybdenum and niobium in the nickel-chromium matrix which provides high resistance to the material without the need for specific heat treatments or precipitation of intermetallic compounds 5 This alloy may contain carbides in the form of MC, M6C and M23C6, rich in Nb, Mo and Cr6. This particular material stands out due to its excellent characteristics which include a combination of good ductility with high tensile and creep resistance, as well as high resistance to high temperatures, even when exposed to severe environments for extended periods 7,8 Given this combination of mechanical properties, one of the possible applications of these materials would be as structural components in the pre-salt industry
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