The Characteristic And Effect Factors Of Single Crystal Nibased Superalloys During High Temperature Creep

The stacking fault energy (SFE) of Ni-Al-W and Ni-Al-Co alloys have been calculated by means of the thermodynamic method, an investigation have been made into the effect of the elements Al, W, Co on the stacking fault energy (SFE) of Ni-base alloys. The crystal lattice parameters and, misfits of the y',y phases in the alloys with different composition have been calculated by means of the experiential formula. Heat treatment conditions of the superalloy 4 have been determined by the analysis of the differential thermal curve (DTA). And the regularity of the microstructure evolution, the effects of the elements on the creep resistance and the deformation mechanism of the alloy during creep are studied by means of the measurement of the rafted rate of the cuboidal y' phase and the internal frictional stress of dislocation movement, and microstructure observation of SEM and TEM.The results show that the element Al decreases the stacking fault energy (SFE) of Ni-W and Ni-Co alloys, the elements W and Co may enhance the SFE of Ni-Al alloy. The SFE of Ni-Al-W and Ni-Al-Co alloys are increased with the temperature. The 'window' of heat treatment for superalloy 4 is delected to be 48 ℃, in the further, the heat treatment conditions of the one is determined as follows: 1280 ℃, 2h, + 1300 ℃, 4h, A.C + 1040 ℃, 4h, A.C. + 870 ℃, 24h, A.C. The average internal frictional stress (σ₀) of dislocations movement during steady state creep have improved slightly with the enhancement of the applied stress, but obvious reduced with the increase of temperature. The effect of the element W on the solution strengthening is better than the one of the element Mo, the action of the stabilizing γ phase volume fraction during creep may be improved with the increase of the element Ta. Compared with other superalloys, the alloy 4 with the less lattice misfit possesses the bigger internal frictional stress and activate energy during creep, so has a better creep resistance and longer the rupture lifetime.The rafted rate of y' phase is related to the applied stresses and temperatures condition, and enhanced with the increase of the applied stresses and temperatures. Much more the elementsW and Ta with the higher melting temperatures in superalloy 4 may decrease the diffusion rate of the other elements in the y matrix, so that prolong the time of γ phase rafted. The fact that the cuboidal y' phase is rafted into the N-type structure during creep can effectively hinder the movement of dislocations, and enhance the creep resistance of superalloy. It is a main reason of maintaining the longer rupture lifetime of the superalloy 4 that the finer cuboidal y' phase is precipitated in the channel of y matrix. The deformation mechanism of the superalloy 4 during primary creep is l/2<110> dislocations activated in the y matrix channel. In the further, the number of dislocations increases as creep goes on, the 1/2<110> super-dislocations of the screw and edge in character shearing into the rafted γ phase are the main deformation mechanism of the alloy in the later creep stage.