Uniaxial and cyclic deformation behavior of selective laser melted GH4169 superalloy at elevated temperature: Insights into Portevin–Le Chatelier effect and strain-amplitude softening

This study presents a comprehensive experimental investigation on the plastic deformation behavior of selective laser melting (SLM) fabricated GH4169 superalloy at an elevated temperature of 500 °C, focusing on uniaxial tension and strain-controlled low-cycle fatigue (LCF). The as-fabricated material, after a specific heat treatment schedule, exhibits a relatively random grain orientation with an average grain size of 43.6μm and a high proportion of annealing twins. Monotonic tensile tests reveal serrated plastic flow, known as the Portevin–Le Chatelier (PLC) effect, characterized by a transition from C-type to superimposed D-type serrations with increasing strain. Under identical temperature conditions and comparable microstructural states, the critical strain associated with serration onset is demonstrated to be exclusively governed by the strain rate. Furthermore, under cyclic loading, the PLC serration type evolves from C-type to A-type, a phenomenon attributed to solute segregation saturation at grain boundaries caused by repeated reverse dislocation motion. Low-cycle fatigue tests show that the fatigue life of SLM-GH4169 is comparable to its conventionally forged counterparts, with fatigue cracks initiating from unmelted powder particles or agglomerated regions. The alloy demonstrates significant cyclic softening, which is strain amplitude-dependent. Microscopic analyses indicate that this behavior is governed by the competitive evolution of friction stress (enhanced by the formation of nano-scale γ^′′ precipitates) and back stress (reduced due to the annihilation of annealing twins under high strain amplitudes). These findings provide valuable insights into the high-temperature deformation and damage mechanisms of additively manufactured nickel-based superalloys.