Fracture Behavior and Fatigue Performance of Inconel 625

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.

因科奈尔625（Inconel 625）是一种镍基高强高温合金，广泛应用于航空航天构件、核工业领域，尤其在海事行业中应用广泛。诸如因科奈尔625这类材料，凭借其优异的抗拉伸腐蚀性能、抗氯离子与硫化物离子诱导的点蚀及缝隙腐蚀能力，同时具备抗微生物腐蚀特性，已被广泛应用于巴西盐下地层的石油勘探作业中。在这类勘探环境中，所有原油开采相关构件都会因自然产生的海洋振荡产生机械疲劳。实验样品经精密加工后，分别按照ASTM E8M与ASTM E466标准，在载荷比R=-1的条件下开展了单轴拉伸试验与拉压循环疲劳试验。研究人员根据该材料的屈服强度，选取586、472、382与306 MPa四组拉伸强度值，用于构建应力-寿命曲线（S-N curve）。针对失效模式开展的宏观与微观结构表征结果显示，裂纹扩展的稳定阶段以疲劳条纹为主要特征，而快速断裂区则以微孔聚合现象为主导。因科奈尔625的微观组织经过细化，由平均尺寸为14 μm的等轴晶粒构成，该组织形态符合经硬化处理后再结晶所获得的细化组织典型特征。分散于因科奈尔625奥氏体基体中的MC型碳化物（M=Mo或M=Nb）与Cr23C6析出相，可通过析出强化机制实现合金的二次硬化。