Effect of cyclic straining at elevated-temperature on static mechanical properties, microstructures and fracture behavior of nickel-based superalloy GH4145/SQ

Abstract

A series of experiments, including constant amplitude low-cycle fatigue tests, uniaxial tension failure tests, TEM observations and SEM examinations, were carried out to investigate the effect of cyclic straining at a temperature of 538 °C on the static mechanical properties, the deformation microstructures and the fracture behavior of nickel-base superalloy GH4145/SQ. The change characteristics of the various basic static mechanical property parameters, such as the yield strength ( σ 0.2), the ultimate strength ( σ b), the modulus of elasticity ( E), the reduction of area ( φ f), the elongation ( δ) and the strain-hardening exponent ( n), during elevated-temperature low-cycle fatigue of the alloy were obtained experimentally and their micromechanisms were further discussed through analyzing both deformation microstructures and fracture features of the cyclically deformed specimens. A composite static mechanical property parameter called static toughness ( U t) was proposed to characterize comprehensively the variation of the various basic static mechanical property parameters ( σ 0.2, σ b, φ f and n), and an approximate formulation describing the exhaustion of the static toughness during high-temperature fatigue failure process was constructed. A quantitative correlation between the exhaustion of the static toughness and the dissipation of the cyclic plastic strain energy during the course of high-temperature fatigue failure of the current alloy was developed in theory and further verified in experiment.