Multi-phase field model simulation based on MPI+OpenMP parallel: Evolution of seaweed and dendritic structure in directional solidification

Abstract

A multi-phase model was established to imitate the growth of algal and dendritic grains during directional solidification. We studied the effects of temperature on the growth of bi-crystals and quantitatively analyzed the influence of anisotropic strength, thermal gradient, and pulling velocity on the evolution of bi-crystals. The results show that both weaker anisotropy strength and smaller pulling velocity can maintain the formation of seaweed tissue. The increase in the pulling velocity can degenerate the seaweed grains into dendrites and improve the growth rate of the dendrites, which make grain B produce more spindles, thereby accelerating the elimination of grain A. The thermal gradient is inversely proportional to the average initial spacing of dendrites. When the thermal gradient is too small, dendritic dendrites produce developed secondary dendrite arms, which, in turn, develop into tertiary dendrite arms to occupy the grain boundary, accelerating the elimination of seaweed grains. In addition, the multi-phase field model is solved by using central processing unit serial computation, single MPI (message passing interface) parallel programming method calculation, and MPI+OpenMP hybrid parallel programming structure, and the relevant factors affecting the efficiency of program operation are analyzed and tested. By comparing the computational efficiency of the three methods, it can be seen that the MPI+OpenMP hybrid parallel programming technology can make full use of computing resources in the case of large computing scale, further optimize the MPI parallel model, and obtain a higher acceleration ratio.

The Effect of Pulling Speed on the Structure and Properties of DZ22B Superalloy Blades

“…Pulling speed has always been one of the most important process parameters in the directional solidification process of DZ22B superalloy blades, which affects the growth rate of dendrite tips, is closely related to the temperature gradient of the leading liquid phase of the solid-liquid interface, and also affects the occurrence of various defects in the casting process [13][14][15][16][17][18][19][20]. Therefore, the method of combining experiment and numerical simulation is used to study the effect of pulling speed on grain and dendrite growth of DZ22B superalloy blades [21], and the optimization parameters can be proposed in a targeted manner.…”