Mechanisms of effect of element P on properties at high temperatures of GH4738 alloy

An investigation is conducted into the mechanisms by which varying levels of phosphorus （P） affect the high-temperature properties，particularly the stress rupture properties，of GH4738 alloy. This is achieved through the use of scanning electron microscopy（SEM），transmission electron microscopy（TEM），electron backscatter diffraction（EBSD）analysis，and molecular dynamics simulations. Stress rupture experiments reveals that the optimal stress rupture properties of GH4738 alloy are obtained when the phosphorus content is increased from 0.004%（mass fraction） to 0.0091%. Beyond this range，an increase in phosphorus content lead to a decline in stress rupture properties. Further microstructural analysis and molecular dynamics simulations demonstrates that phosphorus tends to segregate at grain boundaries，enhancing the cohesion force and bonding energy of these boundaries. Additionally，phosphorus interacts with carbides at grain boundaries to influence stress rupture properties. Specifically，as the phosphorus content increases from 0.004% to 0.0091%，M23C6 carbides at grain boundaries gradually transition from a small，discrete distribution to a discontinuous chain-like distribution. This enhances the pinning effect on dislocations，effectively suppressing their movement and resulting in improved stress rupture properties. However，when the phosphorus content reaches a certain threshold，such as 0.019%，the morphology of M23C6 carbides at grain boundaries changes to a plate-like shape，leading to a decrease in stress rupture properties.