First-principles Studies On The Formation Mechanism Of Hydrogenated Vacancy At ?/?' Phase Interface And Its Effects On The Properties Of Phase Interface In Nickel-based Single Crystal Superalloys

Nickel-based single crystal superalloys are widely used in the aerospace engine and steam turbine industries due to their excellent high-temperature structural stability and good mechanical properties.However,due to its thermodynamic instability and low mechanical strength,the?/??phase interface has always been a hidden danger of nickel-based single crystal superalloys,which has seriously affected the safety of the use of superalloys.Therefore,how to improve the stability and bonding strength of the?/??phase interface becomes the key to the development of nickel-based single crystal superalloys.At present,domestic and foreign researchers have conducted a large number of experimental studies on the alloying element doping in the?/??phase interface,but there are still disputes about the synergistic effect of vacancies and hydrogen atoms in the phase interface and the formation of hydrogenation vacancies in the phase interface.The mechanism needs to be studied in depth.Therefore,based on the first-principles of density functional theory,this paper has studied the formation mechanism of hydrogenation vacancies and the influence of hydrogenation vacancies on the mechanical properties of the?/??phase interface.The main research contents and conclusions are as follows:(1)The preferential formation position of a single vacancy in the?/??phase interface and the preferential occupancy tendency of a single hydrogen atom are studied.The calculation results show that the corner atoms located on the(001)atomic plane of the?phase are most likely to form vacancies;hydrogen atoms preferentially occupy the octahedral interstitial positions at the phase interface.(2)By calculating the substitution doping and interstitial doping of hydrogen atoms in the?/??phase interface,it is found that due to the mutual attraction of vacancies and hydrogen atoms,hydrogen atoms occupy the octahedral interstices nearest to the vacancies to form a stable defect complex.The hydrogen atom deviates from the body center position of the octahedron due to the attraction of the vacancy.Further charge density maps and differential charge analysis show that there is charge transfer between vacancies and hydrogen atoms,which promotes the formation of hydrogenation vacancies.(3)The influence of hydrogenation vacancies on the thermodynamic stability and fracture strength of the?/??phase interface is studied.It is found that hydrogenated vacancies(Vac-H)can improve the thermodynamic stability of the vacancy-containing?/??phase interface;the initial fracture position of the defect-free?/??phase interface is(001)??||(002)?,which is vacant Existence reduces the fracture work of the?/??phase interface,but does not change the fracture position of the?/??phase interface.The existence of hydrogenation vacancies not only reduces the fracture strength of the?/??phase interface,but also changes the fracture position of the phase interface from(001)??||(002)?to(002)??||(001)?.(4)The stable configurations of hydrogenated vacancy(Vac-H_n)in the?/??phase interface under different hydrogenation degrees and their influence on the mechanical properties of the phase interface are calculated.The results show that in the hydrogenated vacancy(Vac-H_n)configuration with different hydrogenation degrees(n=1?6),the hydrogenated vacancy(that is,Vac-H₆)has the highest stability when n=6.Analyzing the differential charge and the enthalpy of formation before and after doping,it is found that as the degree of hydrogenation increases,the stability of the vacancy-containing?/??phase interface continues to increase.When n<5,the existence of hydrogenation vacancies makes the fracture work at the(002)??||(001)?fracture position gradually decrease,while the fracture work at the(002)??||(001)?fracture position gradually increases.When n=6,the octahedral interstice of the nearest neighbor of the vacancy is filled with hydrogen atoms,which causes the fracture work of the two fracture positions to decrease at the same time.