High-Cycle Fatigue and Fracture Behavior of Hastelloy C276
摘要
The present investigation systematically examines the high-cycle fatigue behavior of Hastelloy C276, a Ni-Cr-Mo-based superalloy widely recognized for its exceptional corrosion resistance and use in demanding engineering environments. Stress-controlled high-cycle fatigue tests were conducted using a rotating-beam fatigue testing machine to replicate the alternating tensile–compressive stress states encountered in real-world applications. Microstructural analysis confirmed a homogeneous γ-matrix with annealing twins and absence of carbide precipitation, consistent with a solutionized condition. Mechanical testing established a yield strength of 427 MPa, an ultimate tensile strength of 806 MPa, total elongation of 72%, and a bulk hardness of 200 HV. Fatigue experiments conducted at stress amplitudes between 507 and 602 MPa demonstrated lifetimes ranging from 104 to 106 cycles, thereby confirming the alloy’s classification as a high-cycle fatigue material even at stresses exceeding its yield strength of 427 MPa. Fractographic analysis revealed the classical three-stage fatigue mechanism—crack initiation, stable crack propagation, and final overload failure. Striation spacing varied between 0.5 and 5.0 µm, with a clear dependence on applied stress amplitude: widening progressively up to 546 MPa, then showing localized refinement and overlapping features at higher loads. The presence of microvoids, dimples, and honeycomb morphology in the overload region further confirmed ductile fracture behavior. These results establish Hastelloy C276 as a high-performance material with superior fatigue resistance, supported by quantitative correlations between hardness, tensile strength, and fatigue life, and validated through rotating-beam fatigue testing. The safe fatigue strength of the material was found to be 432 MPa for 107 cycles. For stresses below 432 MPa, the material does not fail.