Nano-twin-induced exceptionally superior cryogenic mechanical properties of a Ni-based GH3536 (Hastelloy X) superalloy

Abstract

The GH3536 (Hastelloy X) superalloy is one of the most widely used Ni-based sheet alloys for gas turbine hot parts. To investigate its relationship among the processing, microstructure, and mechanical properties, GH3536 alloy was fabricated from pure constituent elements by arc melting and drop casting. The drop-cast ingots were homogenized, cold rolled, and recrystallized to obtain single-phase microstructure with average grain size of ∼12 μm. Tensile tests were then performed at a wide temperature range between 77 K and 1,073 K. Surprisingly, although this alloy was developed for high temperature use, it has extraordinary cryogenic mechanical properties. Moreover, the yield strength, ultimate tensile strength, and elongation to fracture increased dramatically with decreasing temperature, exactly the same behavior as that of recently developed face-centered cubic medium/high-entropy alloys (M/HEAs). Transmission electron microscopy was used to study the deformation mechanisms of GH3536 alloy at 77 K and room temperature. Deformation-induced nano-twins were observed after interrupted/fracture tests at 77 K, but rarely in specimens tested at room temperature, where plasticity occurred exclusively by dislocation gliding. The similarity between this 70-year-old GH3536 (Hastelloy X) alloy and M/HEAs, which is recently considered as the revolution in alloy design, will be discussed from the viewpoint of the microstructure, entropy calculation, mechanical properties, and deformation mechanism.