In this paper, the deviation from eutectic composition in boundary layer for eutectic growth is studied by phase-field method. According to a series of artificial phase diagram, the lamellar eutectic growth of these alloy is simulated during directional solidification. At steady state, average growth velocity of eutectic lamella is equal to the pulling velocity. With the increasing of the liquidus slope of β phase, the average composition in boundary layer would deviate from eutectic composition and the deviation increases. The constitutional undercooling difference between both solid phases caused by the deviation increases with the increasing of the deviation. The β phase would develop a depression under the influence of the deviation.

Eutectoid growth, as the important reaction mechanism of the carbon steel heat treatment, is the basis to control the microstructure and

performance. At present, most studies have focused on lamellar growth, and did not consider the nucleation process. Mainly due to the

nucleation theory is inconclusive, a lot of research can support their own theory in a certain range. Based on the existing nucleation theory,

this paper proposes a cooperative nucleation model to simulate the nucleation process of eutectoid growth. In order to ensure that the

nucleation process is more suitable to the theoretical results, different correction methods were used to amend the model respectively. The

results of numerical simulation show that when the model is unmodified, the lateral growth of single phase is faster than that of

longitudinal growth, so the morphology is oval. Then, the effects of diffusion correction, mobility correction and ledges nucleation

mechanism correction on the morphology of nucleation and the nucleation rate were studied respectively. It was found that the

introduction of boundary diffusion and the nucleation mechanism of the ledges could lead to a more realistic pearlite.

The main work of this paper focuses on the simulation of binary alloy solidification using the phase field model and adaptive octree grids.

Ni-Cu binary alloy is used as an example in this paper to do research on the numerical simulation of isothermal solidification of binary

alloy. Firstly, the WBM model, numerical issues and adaptive octree grids have been explained. Secondary, the numerical simulation

results of three dimensional morphology of the equiaxed grain and concentration variations are given, taking the efficiency advantage of

the adaptive octree grids. The microsegregation of binary alloy has been analysed emphatically. Then, numerical simulation results of the

influence of thermo-physical parameters on the growth of the equiaxed grain are also given. At last, a simulation experiment of large scale

and long-time has been carried out. It is found that increases of initial temperature and initial concentration will make grain grow along

certain directions and adaptive octree grids can effectively be used in simulations of microstructure.

Wire and laser additive manufacturing (WLAM) can produce outstanding mechanical properties of GH3039 nickel-based superalloys. A quantitative rapid phase field model with solute trapping kinetics has been developed during the rapid solidification process, where a range of process conditions are considered in terms of thermal gradients and pulling speeds. Intergranular hot cracking is found to occur at boundaries of tilted columnar dendrite in the GH3039 nickel-based superalloys. The simulations demonstrate that the phase field model considering the interface deflection can represent the dendrite growth during additive manufacturing more realistically. With the aid of numerical simulations, it is determined that dendrite growth morphologies transform from symmetrical columnar dendrite to tilted columnar dendrite as the interface crystallographic deflection is increased, while increasing the deflection angle can lead to uneven composition of material matrix, especially at the columnar dendrite interface. Solute concentrations at the columnar dendrite interface tend to promote hot cracking in additively manufactured Ni-based superalloy.

Tilted columnar dendritic morphologies are usually existed in wire and laser additive manufactured parts of GH3039 alloy. Overgrowth behaviors induced by the tilted dendritic arrays with a large tilted angle, and the effect of the angle between the growth direction and the direction vertical locally to the solid substrate on primary spacing, solute concentration and morphological evolution have been investigated at both the converging and the diverging grain boundaries through the phase-field simulation. The formation of cracking depends on solidification behaviors including columnar dendrites growth and micro-segregation in the interdendritic region. Furthermore, the effect of the tilted columnar dendrites on the susceptibility of crack is investigated during wire and laser additive manufacturing.