Tensile deformation and fracture characteristics of delta-processed Inconel 718 alloy at elevated temperature

Three specimens with different initial δ phase contents have been used to study the tensile deformation and fracture characteristics of the delta-processed Inconel 718 alloy at elevated temperatures by tensile tests at 950 °C. The results indicated that the tensile stress–strain curves of the three specimens were the elastic-uniform plastic curves, and there were two deformation processes during the uniform plastic deformation stage of the delta-processed specimens. The strain hardening exponent in the first deformation process was higher than that in the second process, and the value of the strain hardening exponent increased as the content of δ phase increased. In addition, the plasticity of the specimen at elevated temperatures decreased as the content of δ phase increased. However, the fracture mechanisms for all the specimens were all microvoid coalescence ductile fracture, and the δ phase and carbide were the nucleuses for the formation of micropores. The elongation for the specimen with 8.21% pre-precipitated δ phase was still as high as 80%. Thus, delta-processed Inconel 718 alloy presented excellent high-temperature plasticity.