Multiscale Study Of Interactions Between Atoms And Phase Stability In Nibased Superalloys

Ni-based single-crystal superalloys have been used widely in advanced aeroplane fields due to their excellent mechanical properties at elevated temperature.Different alloying elements with varying contents,which can stabilize the microstructures of the Ni-based singlecrystal superalloys,have been added to enhance the mechanical properties of Ni-based singlecrystal superalloys.The addition of refractory elements to these superalloys,such as rhenium and tungsten,can significantly improve the strength of Ni-based single-crystal superalloys by solid-solution hardening,while the addition of Al can form ??-Ni3 Al precipitate from ?-Ni matrix and enhance the mechanical properties of Ni-based single-crystal superalloys by secondphase strengthening.Therefore,the investigation on atomic interactions of alloying elements and their alloying effect on phase stability in Ni-based single-crystal superalloys is of great of significance in both science and engineering application.By combining the first-principles method and statistical thermodaynamical Monte Carlo simulation,the atomic interactions and phase stability of Ni-based single-crystal superalloys can be investigated and predicted.Firstly,we have investigated the magnetic monment change of Ni and alloy lattice expansion behavior induced by adding different amounts of Re into the Ni-Re binary alloys.Then the first-peinciples method has been used to study the atomic interactions and the stability of ordered structures in Ni-rich Ni-Re alloy at elevated and low temperatures,our calculated results show that the D1a-Ni4 Re ordered structure is the most stable precipitation in the Ni-rich Ni-Re alloys.Finally,using the atomic interactions obtained from first-principles calculations,we have used the statistical thermodaynamical Monte Carlo simulation to predict the order-disorder transition in the Ni-9at.%Re alloy from 1200 K to 300 K,we have also compared our obtained order-disorder transition temperature and short-range parameters to the experimental values for Ni-9at.%Re alloy,our results agree well with the experiment.Secondly,we have also investigated the W solid solution Ni-W binary alloy by using the similar investigation procedure of Ni-Re,moreover,we have particularly studied the orderdisorder transition temperatures and final precipitates in Ni-W alloys with different W concents.Our result show that the W content also affects the lattice parameter of the Ni-W alloy and the atomic interaction between atoms as well as the magnetic moment of Ni in the Ni-W alloy,we also find that the Ni-W alloys have strong tendency to form ordered phase even at elevated temperatures,however,the most stable precipitate in the Ni-W alloys is determined by the W content.Based on the atomic interactions obtained from first-principles calculations,we have used the statistical thermodaynamical Monte Carlo simulation to investigate the order-disorder transition in Ni-W alloys within the W content range of 1-35 at.%W,our results show that W content affects the order-disorder transition temperatures and the final precipitates in Ni-W alloys.Our results also show good agreement with the existing experimental findings and can have significant contribution to the order-disorder transition in the Ni-rich Ni-W alloys.Finaly,we have further investigated the atomic interactions and the phase stability in NiAl-Re ternary alloys with a focus on the Re effect on the formation of ??-Ni3 Al precipitate from ?-Ni phase.Our calculated results for the Ni-Al alloy show that Ni-Al alloys have strong tendency to form ordered phase even at elevated temperatures,while ??-Ni3 Al precipiate in the L12 crystal structure is the most stable phase.Our predicted order-disorder transition temperature of ??-Ni3 Al in ?-Ni agrees well with experimental values,moreover,we also find that the order-disorder transition temperature of ??-Ni3 Al increases with the increasing of Al content in Ni-Al alloys.In the Ni-Al-Re ternary alloys,our results also indicate that the orderdisorder transition temperature of ??-Ni3 Al increases with the increasing of Re content,while the Re element prefers to segregate to the ?-Ni phase side in the ?-Ni/??-Ni3 Al interface system and forms the Re cluster in a few-atom scale.By comparing the Re atomic interactions in ??-Ni3 Al and ?-Ni phases,we conclude that the stronger repulsive interaction between Re atoms in ??-Ni3 Al phase contributes the partitioning of Re to the ?-Ni phase of the ?-Ni/??-Ni3 Al interface system.