Determination of relationship between high-temperature low cycle fatigue damage and mechanical property degradation: Experimental and theoretical analyses

Abstract

Mechanical properties of metallic materials gradually degrade under high-temperature low cycle fatigue (HTLCF) loading, which is a manifestation of fatigue damage accumulation. In this study, a mapping modeling is developed to determine the relationship between micro-scale HTLCF damage and macro-scale mechanical property degradation. Strain-controlled HTLCF tests in GH4169 superalloy are carried out at 650 °C and interrupted at various lifetime fractions for subsequent microscopic characterizations and high-temperature tensile tests. Quantitative analysis of electron backscatter diffraction indicates a three-stage increase in kernel average misorientation and geometrically necessary dislocation throughout the cyclic process, along with variations in the fraction of different grain boundaries. Simultaneously, the evolutions of shearing precipitate and de-twinning are characterized using transmission electron microscope. Furthermore, the mechanical properties of GH4169 superalloy, such as yield strength, ultimate tensile strength, elongation and work-hardening rate, demonstrate different degradation characteristics after exposure to HTLCF damage. Based on these results, the mechanism of HTLCF-induced mechanical property degradation is clarified and the mapping modeling is established using tensile plastic strain energy density and kernel average misorientation. Finally, a damage level evaluation method for engineering components is developed after the generality and flexibility of model is verified in different high-temperature materials.