The properties of an alloy are determined by the microstructure.
The techniques to predict the microstructure is essential to designing new alloys
Ni-base superalloys is heat-resistant alloys have been used in plant and aircraft engines due to their high-temperature strength, ductility, creep resistance and fatigue fracture resistance properties at a high temperature, above 650 ℃.
The microstructure of Ni-base superalloys consists of the Υ'-L12 phase, the topologically closed packed phase, carbides, borides and etc., and they affect mechanical properties of Ni-base superalloys.
Therefore, in order to design new alloys, predicting the microstructure is an important part of predicting the mechanical properties.
In particular, microstructural factors have a decisive effect on the mechanical properties.
Locq, D, and P Caron. 2011. “On Some Advanced Nickel-Based Superalloys for Disk Applications.” AerospaceLab (3): 1–9.
1. First-principles Calculation
· Calculation of planer defect energy
In the Ni-base superalloys, various deformation mechanisms (Orowan mechanism, cutting mechanism, and shearing mechanism) are presented by given temperature and applied stress.
Since mechanical properties such as strength, creep resistance and fatigue resistance are affected by the change of these deformation mechanisms, it is very important to understand these deformation mechanisms.
These deformation mechanisms are related to the antiphase boundary energy, complex stacking fault energy, superlattice intrinsic/extrinsic energy in ’-L12 phases, so many researchers try to estimate these energies.
However, in practice, since it is difficult to obtain these energies experimentally, these energies have been obtained using the first-principles calculation.
In present, the principles of these deformation mechanisms have been not clarified completely, but verified partially.
Based on the experimental results and calculation data that have been obtained so far, if these deformation mechanisms are studies continually, it is expected that it will be helpful in designing the new alloys.
Smith, T.M. et al. 2015. “Segregation and η Phase Formation along Stacking Faults during Creep at Intermediate Temperatures in a Ni-Based Superalloy.” Acta Materialia 100: 19–31.
Titus, Michael S., Yolita M. Eggeler, Akane Suzuki, and Tresa M. Pollock. 2015. “Creep-Induced Planar Defects in L12-Containing Co- and CoNi-Base Single-Crystal Superalloys.” Acta Materialia 82: 530–39.
Eurich, N.C., and P.D. Bristowe. 2015. “Segregation of Alloying Elements to Intrinsic and Extrinsic Stacking Faults in ’-Ni3Al via First Principles Calculations.” Scripta Materialia 102: 87–90.
Breidi, A., J. Allen, and A. Mottura. 2018. “First-Principles Modeling of Superlattice Intrinsic Stacking Fault Energies in Ni3Al Based Alloys.” Acta Materialia 145: 97–108.
2. Thermodynamic Calculation
· Alloy Designs
The thermodynamic calculations have been used to design Ni-base superalloys.
In order to design these alloys, the formation of TCP phases that weaken the mechanical properties should be controlled.
The thermodynamic calculations enable to predict the generation of TCP phases in multi-component alloy systems.
In addition, the quantity of ’-L12 precipitations significantly affects mechanical properties.
The thermodynamic calculations can calculate the quantity of ’-L12 precipitations, so many researchers have tried to estimate the mechanical properties through the thermodynamic calculation.
In practice, some researchers predicted the mechanical properties for unknown Ni-base superalloys by using a method that combines the thermodynamic calculations with empirical models or machine learning models optimized from previous experimental data.
Collins, D. M., and H. J. Stone. 2014. “A Modelling Approach to Yield Strength Optimisation in a Nickel-Base Superalloy.” International Journal of Plasticity 54: 96–112.
Reed, R.C., T. Tao, and N. Warnken. 2009. “Alloys-By-Design: Application to Nickel-Based Single Crystal Superalloys.” Acta Materialia 57(19): 5898–5913.
Kim, Young-Kwang et al. 2016. “An Intermediate Temperature Creep Model for Ni-Based Superalloys.” International Journal of Plasticity 79: 153–75.
Conduit, B. D., N. G. Jones, H. J. Stone, and G. J. Conduit. 2017. “Design of a Nickel-Base Superalloy Using a Neural Network.” Materials and Design 131(June): 358–65.
Kim, Young-Kwang et al. 2018. “A Numerical Model to Predict Mechanical Properties of Ni-Base Disk Superalloys.” International Journal of Plasticity 110: 123–44.
Young-Kwang Kim, Ph.d.
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