Theoretical Study On Plasticity-induced Stacking Fault Behaviors And Intrinsic Mechanical Properties Of Novel γ/γ’ Co-based Superalloys

The rapid development of aviation industry has continuously put forward higher demands for the temperature-bearing capacity of the new generation of high thrust-to-weight ratio aeroengine turbine blade materials.However,due to the limitation of the melting point of Ni,the temperature-bearing capacity of nickel-based superalloys,which are currently the most widely used on high-pressure turbine blades at the hot end of aero-engines,can not longer satisfy the further development of the aviation industry.Finding a new generation of hightemperature structural materials with higher service temperature and environmental resistance is a practical engineering problem that needs to be solved urgently in the development of aerospace,energy and power industries.The γ’ precipitation-strengthened cobalt-based alloy discovered in recent years is considered a strong candidate for the next generation of hightemperature materials due to its higher solid solution temperature and excellent hightemperature environmental resistance.By adding Ni,Ti,Ta and other alloying elements,alloying treatment is the main method to improve the mechanical properties of cobalt-based alloys in experimental research.However,at present,the micro-mechanism and high-temperature mechanical properties of these key elements affecting the mechanical behavior of cobalt-based superalloys are not clear,especially the mechanism that alloying affects the sliding stacking fault behavior caused by plastic deformation.However,these microscopic deformation behaviors are difficult to characterize through experiments.In view of this,this paper uses density functional theory to study the relationship between the generalized stacking fault energy of the key y’ phase and its composition,and reveals the relationship between dislocation slip and plastic deformation.In addition,the change law of the intrinsic mechanical properties of the key phases in the alloy with temperature is studied,in order to provide theoretical support for the modification of the new cobalt-based superalloy.Using the first-principles method,this paper systematically calculated the generalized stacking fault energy,twinning nucleation ability parameters,high-temperature mechanical properties(elastic constant,polycrystalline modulus,toughness/brittleness criterion value,theoretical hardness,etc.)and thermodynamic properties.The effects of Ni,W,Ta and Ti on the stacking fault behavior and mechanical properties of the γ’ phase were researched.This article conducts research from the following aspects:the influence of Ni and Al/W on the sliding and stacking fault behavior of γ’ precipitates(Chapter 3);the coupling effect of Ta and Ti on the sliding and stacking fault behavior of γ’ precipitates(Chapter 4);Intrinsic mechanical properties of alloy doping modified γ’ precipitate phase(Chapter 5).The results of this paper show that the deformation mechanism of γ’phase is closely related to its generalized stacking fault energy and stacking fault energy barrier.Doping with appropriate amounts of Ni and W can increase the strength of the alloy and weaken the twinning nucleation ability of the alloy;Ta and The addition of Ti will increase the stacking fault energy of the γ’-Co3(Al0.5W0.5)phase,thereby increasing the strength of the alloy.In addition,the deformation mechanism of the strengthened phase is also affected by the grain loading angle.The change of the doped Ni content will change the angular range of the γ’ phase that the deformation mode can be activated;the addition of W will not only affect the angular range of the deformation mode activation,but also Will change the types that can be activated.With the increase of the content of Ni and W elements,the angular range in which the pseudo twins are activated continues to decrease.The research results based on the stress-strain energy and the quasi-simple Debye model show that alloying Ni will increase the toughness of the alloy γ’phase;adding W can increase the hardness of the γ’ phase and reduce the toughness,but adding excessive W On the contrary,it will reduce the hardness of the γ’ phase;the addition of Ta and Ti elements can also increase the strength and hardness of the γ’phase at the premise of sacrificing toughness.In addition,doping with Ni can also increase the vibration entropy of theγ’ phase.