Kaiming Cheng

Phase-field simulation of liquid phase migration in the WC–Co system during liquid phase sintering

Abstract Liquid phase sintering is a process for forming high performance, multiple-phase components from powders. The process includes very complex interactions between various mass transportation phenomena, among which the liquid phase migration represents an important one in the aspect of forming a gradient structure in cemented carbide. In the present work, phase-field simulation of the liquid phase migration phenomenon during liquid phase sintering is performed in the WC – Co based cemented carbide. The simulation results are analyzed and compared with the experimentally determined key factors of microstructural evolution, such as contiguity and liquid phase migration rate. The diffusion-controlled solution–precipitation mechanism of the liquid phase migration process in the cemented carbide system is confirmed from the current simulation result, which provides deeper understanding of the microstructural evolution during the liquid phase migration process. These simulations can offer guidance in preventing the liquid phase migration process during liquid phase sintering of cellular cemented carbide.

Developing Cemented Carbides Through ICME

The ICME (Integrated Computational Materials Engineering) for cemented carbides aims to combine key experiments with multi-scale simulations from nano (10−10~10−8 m) to micro (10−8~10−4 m) to meso (10−4~10−2 m) and to macro (10−2~10 m) during the whole R&D process of cemented carbides. Based on ICME, the framework for R&D of cemented carbides, involving end-user demand, product design and industrial application, is established. In this work, a description to our established thermodynamic and thermophysical (diffusion coefficient, interfacial energy, and thermal conductivity and so on) databases is presented, followed by simulation of microstructure evolution during sintering of cemented carbides by means of phase field method. Work is also done to investigate the correlation between microstructure and mechanical properties (crack, stress distribution, and coupled temp-displacement) by using phase field and finite element methods. The proposed ICME for cemented carbides is used to develop a few new cemented carbides (including double layer gradient cemented carbides and γ′-strengthened Co–Ni–Al binder cemented carbides), which have found industry applications.

Development of Gradient Cemented Carbides through ICME Strategy

An integrated computational materials engineering (ICME) including CALPHAD method is a powerful tool for materials process optimization and alloy design. The quality of CALPHAD-type calculations is strongly dependent on the quality of the thermodynamic and diffusivity databases. The development of a thermodynamic database, CSUTDCC1, and a diffusivity database, CSUDDCC1, for cemented carbides is described. Several gradient cemented carbides sintered under vacuum and various partial pressures of N2 have been studied via experiment and simulation. The microstructure and concentration profile of the gradient zones have been investigated via SEM and EPMA. Examples of ICME applications in design and manufacture for different kinds of cemented carbides are shown using the databases and comparing where possible against experimental data, thereby validating its accuracy.