Effect Of Ta On The Microstructure And Long-term Creep Property Of A Nickel-based Single Crystal Superalloy

Advanced heavy-duty gas turbines have become the key equipment to achieve the goals of energy conservation,emission reduction and development of new clean power energy.As the temperature of the inlet of the turbine engine continues to increase,higher requirements are put forward on the mechanical properties of the superalloys.In this paper,in response to my country's future G and H-class gas turbines' demand for second-generation nickel-based single crystal superalloys,methods such as scanning electron microscopy(SEM),transmission electron microscopy(TEM),and energy spectrum analysis(EDS)are used.to study the influence of Ta with different content(2Ta,5Ta and 8Ta)on the long-term creep behavior at 900? and the law of the structure damage-propertis degradation during long-term thermal exposure at 900? of a hot corrosion resistant Ni-based single crystal superalloys,and find out the difference of creep deformation behavior between long-term creep and short-term creep of the alloy.As the Ta content increases from 2%to 8%,the cubic degree and content of ?' phase increased significantly,the lattice misfit of alloy continues to increase,and the driving force of the rafted ?' phase also increases markedly.In addition,the addition increase of Ta content also significantly affects the rafted structure of the alloy.During creep deformation at 900?/235MPa,As the Ta content increases from 2%to 8%,the strain during primary state creep and the strain rate during steady state creep of the alloy continue to decrease,and the creep lifetime of alloy is obviously increased.During the primary state creep,The creep deformation of the alloy mainly controlled by the slip and climb of a/2<011>dislocations in the matrix,the dislocation movement ability is limited with the addition increase of Ta content;The dislocation network and raft structure are gradually formed during the steady state creep,the dislocation network formed faster in high-Ta alloy and the dislocation-pair starts to shear the ?' phase in low-Ta alloy;During the tertiary stage creep,As the Ta content increases from 2%to 8%,the number of dislocation pairs in the ?' phase is significantly reduced,but the interfacial dislocation network is denser.Compared with the short-term creep at the same temperature,the dislocation motion is lower,the number of dislocations is less,the formation time of the rafted ?' phase and the dislocation network is obviously retarded during long-term creep process.The long-term creep deformation at high temperature and low stress mainly occurs inside the matrix,and the number of dislocations-pairs is very small except for the area close to the fracture structure.During long-term thermal exposure at 900?,the coarsening behavior of ?' phase is different markedly with the addition increase of Ta content.The coarsening rate of 2Ta and 8Ta alloys is relatively slow,the sze ?' phase do not grow up obviously until after exposure 8000 h.The size of the interdendritic ?' phase of 5Ta alloy increased evidently after 2000 h exposure.The W content in the alloy MC carbide decreases while the Ta content increases significantly,and the time for the precipitation of M23C6 carbides around the MC carbides is obviously retarded is obviously retarded with the thermal exposure extended.The creep behaviors are significantly different for three alloys after exposure for different times:During creep deformation at 900?/275MPa,the creep property of 2Ta alloy exhibits a dramatically decrease until exposure 8000 h instead of a drop decrease after exposure 2000 h and 4000 h in 5Ta and 8Ta alloys.As the Ta content increases from 2%to 8%,the creep life after different exposure time increases first and then decreases.In addition,the creep life after every exposure time increased with the adtion increase of Ta content.