High Temperature Oxidation Analysis And Strength Analysis Of Ultra-supercritical Turbine Blades

Since ultra-supercritical steam turbine units with large capacity,high parameters and high thermal efficiency will be an important development trend of thermal power generation technology in the future,higher performance requirements are also put forward for the unit materials.However,as the steam parameters of the unit increase,it will also cause a series of high-temperature oxidation and corrosion problems of the unit components.Nimonic80A alloy is a kind of aging strengthening alloy,and it has good high temperature oxidation resistance and creep performance and is widely used in steam turbine blade materials.Therefore,this paper takes the first stage blade of the high-pressure cylinder of a domestic 600MW ultra-supercritical steam turbine as the research object,and studies the oxidation mechanism and mechanical properties of the blade material.The main contents and research results are as follows:（1）Based on the density functional theory,the model of Nimonic80A alloy phase was established and the model was evaluated and verified.The oxidation mechanism of γ-Ni₃Cr,γ′-Ni₃Al,γ′-Ni₃Ti phase in Nimonic80A alloy was studied,and the crystals of the alloy phase were analyzed.Surface stability,surface adsorption energy,vacancy concentration and electronic structure.The results show that the vacancy formation energy of Al is the largest in each phase,and the degree of overlap between O orbitals and Al orbitals is greater than that between O and other atoms,indicating that the bonding ability of O and Al atoms is the strongest.（2）Based on the molecular dynamics method,the Nimonic80A alloy model was established,and the model was evaluated and verified.The elastic constant,elastic modulus,Poisson’s ratio,Young’s modulus and anisotropy of the alloy were calculated under different Ti/Al Factor,the effect of different Ti/Al on the elastic properties of Nimonic 80A alloy is analyzed.The results show that as the Ti/Al ratio increases,its elastic constant and Poisson’s ratio show a trend of increasing first and then decreasing.When Ti/Al is 2.5,its Poisson’s ratio and Young’s modulus are the smallest,and their values are respectively 0.2856 and 228.2684Gpa,compared with the Ti/Al ratio of 1,reduced by 13%and 3.4%,respectively.（3）Based on the heat-fluid-solid coupling numerical method,a domestic 600MW ultra-supercritical steam turbine blade model was established and the model was tested and verified.The isentropic efficiency of the blade and the distribution of surface pressure,surface temperature and Mach number at different blade heights were studied.At the same time,the stress and deformation of the stationary blade and the moving blade were studied.The results show that the isentropic efficiency is lower at the outlet of the stationary blade and the leading edge of the moving blade,which is about 80%and 78%,respectively;the Mach number of the blade is less than 0.3 at different blade heights;the total and radial deformation of the stationary blade The distribution showed a similar change trend;the circumferential deformation distribution of the moving blade and the total deformation were similar;the high stress of the stationary blade appeared on the suction surface side of the blade near the middle leading edge,and the high stress of the moving blade appeared near the leading edge of the blade The maximum stress value of the leaf root is774Mpa and 339Mpa respectively.（4）Further study on the deformation and stress distribution of the blade under different Ti/Al ratios,it is concluded that with the increase of Ti/Al ratio,the total deformation of the stationary and moving blades and the maximum equivalent pressure show an increase and then decrease Change trend.The results show that when the Ti/Al ratio is 2.5,the maximum equivalent stresses of the stationary blade and the moving blade are 711Mpa and 329Mpa,respectively,which is 8.1%and 2.9%lower than that when the Ti/Al ratio is 1.When the ratio is 2.5,the maximum deformation of the stationary blade and the moving blade are 7.01mm and 0.38mm,respectively,which is 7.4%and 13.8%lower than that when the Ti/Al ratio is 1.