Phase-Field Moldel For Grain Growth Of Super- Alloy With Second Phase Particles Under Annealing Treatment

Super-alloy with excellent high temperature strength, thermal stability and thermal fatigue resistance, not only is important material in national defense and economic construction, but also a hot field in science research. Some researchers have put forward to improve strengthen and hardness of super-alloy though the second phase particles pinning grain boundary, and others also hope to make the columnar structure to increase creep resistance and fatigue resistance, but such methods are summarized on the basis of experiment,and theory is not perfect enough; Later, famous scholars, such as H.J.Frost and I.Baker, using a front-tracking model to simulate the two experiment processes, then summed up the function between the boundaries mobility and angle and energy, and express the relationship between the strengthening and grain structure. I have learn the simulation measure, and ever read enough materials about the super-alloy strengthening. Therefore, in this paper, the field phase method, one of the most frontier simulation ways in materials science,will be combined to deep the theory and process of super-alloy strengthening. The particular way is building a thermodynamic model which include the second phase particles, then simulating the changes of grain structure from uniform and directional annealing treatment.Conclusions are as follow:1、The second phase particles exist in the boundaries and the intersections of three crystal. When samples be taken by uniform annealing treatment, the particles can show a pinning effect on grain boundary migration. And the higher the annealing temperature, the lager the grain boundary migration energy, the grain boundary is more easy to get rid of the second phase particles, the grain radius will be more lager.2、The effect of second phase particles on grain growth mainly depends on the size and volume fraction of second phase particles. When the diffusion coefficient change in a low range, the second particles didn’t occur coarsening, and it will has a pinning effect on grain boundary.Besides, the higher the volume fraction of the second phase particles,the more obvious the pinning effect.3、When directional annealing processing samples, the thermodynamic parameters and the volume fraction of second phase particles have a significant influence on the formation of the columnar grain structure. And the length of the columnar grain decides the aspect ratio.4、The columnar grain can grow along the orientation of the second phase particles, and particles distance can change the orientation of columnar grain boundary in a certain range.5、There is competition and merging mechanism in columnar grain growth under directional annealing, as coarse columnar grain inhibit the growth of the fine columnar grain and finally merged, or the grain growing along the axial inhibit such deviated from the axial.This paper simulated some small changes of super-alloy structure under directional annealing, revealed the changes mechanism and relationship between strengthening and structure,can guiding the process design for super-alloy would be significant.