Weisheng Cao

Calculation and application of liquidus projection

Abstract Liquidus projection usually refers to a two-dimensional projection of ternary liquidus univariant lines at constant pressure. The algorithms used in Pandat for the calculation of liquidus projection with isothermal lines and invariant reaction equations in a ternary system are presented. These algorithms have been extended to multicomponent liquidus projections and have also been implemented in Pandat. Some examples on ternary and quaternary liquidus projections are presented.

Computational Kinetics Simulation of Precipitation and Dissolution of Gamma Prime (γ′) in Heat Treating and Welding of 718plus Superalloy

The evolution of the strengthening precipitate in a precipitation-hardening alloy, such as the gamma prime (γ′) phase in Ni-base superalloys, during heat treating and welding can affect the resultant mechanical properties significantly. Computational kinetics simulation can be a useful tool for understanding and controlling of such evolution. The present study was conducted to simulate the γ′ precipitation and dissolution during aging and welding of the recently developed Ni-base superalloy 718plus using the PanPrecipitation module of the Pandat software along with available thermodynamic and kinetic databases. The purpose was to demonstrate the application of such software and databases to materials processing including heat treating and welding. The variations in the volume fraction, average precipitation size, and number density of γ′ with time during aging and welding were calculated. The calculated results under aging condition agreed well with the available experimental data, while those under welding also predicted the correct trend.

Simulation of Co-precipitation Kinetics of γ′ and γ″ in Superalloy 718

In this paper, we will study the co-precipitation kinetics of phases in Superalloy 718 using the simulation tool we have developed using the CALPHAD approach. This tool considers concurrent nucleation, growth and coarsening of these precipitates. Furthermore, it is directly integrated with thermodynamic calculation engine to obtain instant update of phase information, such as the composition of the matrix and the nucleation driving force for each precipitate. In addition to the average particle size, the more advanced KWN (Kampmann and Wagner Numerical) model was implemented to allow for predication of the full evolution of the particle size distribution (PSD). In this paper, we will perform virtual experiments using this tool to simulate the co-precipitation of the γ′ and γ″ phases under different heat treatment conditions. Simulation results, such as temporal evolution of volume fraction, number density, and mean size of the precipitates, as well as the final particle size distribution will be presented and discussed. The impact of δ precipitate and the initial microstructure will also be briefly discussed. These virtual experimental results can be used to understand the microstructural features of Superalloy 718 and serve as guidance for further optimization of heat treatment schedule.