Computer Simulation Of Grain Structure Formation In Solidification Of Aluminum Alloy And Superalloy Castings

The control of the grain structure is of primary importance in many solidification processes of castings,because the grain structure has influence on their mechanical properties and operating performances. Although the experiment-based method adopted for the control of the grain structure is widely used for its visualization and simplicity,it does not give much insight into the physical mechanisms responsible for grain structure formation,it also expends much time and money. The computer simulation method that is rising recently has been paid more and more attention because it can counteract the experiment-based method's weaknesses. In this thesis,the grain structure formation in solidification of Al-4wt%Cu alloy and superalloy K4169 castings has been simulated by computer. The evolution of their grain density and grain size during solidification was calculated under various founding processes. The grain nucleation and growth pictures were displayed on the computer screen,the visualization of grain formation by computer has been achieved.1. Using FDM Fortran program,the temperature fields on a cross section of Al-4wt%Cu alloy founding samples,superalloy K4169 cylinder ingots and superalloy K4169 blades were simulated through solving the heat diffusion equation with enthaply formulation. It reflected temperature evolution on the cross section of castings under various founding processes correctly. The simulated results of Al-4wt%Cu alloy founding samples agree well with the measured ones.2. Using the fraction of solid,the simulation of temperature fields,the continuous nucleation model and growth kinetics model of the dendritic tip were coupled to calculate grain structure features of Al-4wt%Cu alloy founding samples,superalloy K4169 cylinder ingots and superalloy K4169 blades. The calculated results agree well with the measured ones.3. Based on a two-dimensional Cellular Automaton technique and the grain structure features of Al-4wt%Cu alloy founding samples,superalloyK4169 cylinder ingots and superalloy K4169 blades,the grains nucleation and growth of these castings were displayed on computer screen dynamically,the visualization of grain formation by computer has been achieved.4. Through investigations for a great number of investment castings of superalloy K4169 cylinder ingots,the continuous nucleation model parameters of superalloy K4169 at different pouring temperatures have been deduced. The grain structure features of superalloy K4169 cylinder ingots during solidification at different pouring temperatures were computed. The visualization of grain nucleation and growth by computer has been achieved. The calculated effect of the pouring temperature on the resultant grain structure agrees well with experimental observations.5. Through investigations for a great number of investment castings of superalloy K4169 cylinder ingots,the continuous nucleation model parameters of superalloy K4169 under various refining processing have been deduced. The grain structure features of superalloy K4169 cylinder ingots during solidification under various refining processing were computed. The visualization of grain nucleation and growth by computer has been achieved. The calculated effect of refiner on the resultant grain structure agrees well with experimental observations.6. In the light of physical mechanism of equiaxed dendrite growth,solute diffusion models for equiaxed growth was improved. The improved model not only describes grain growth,but also describes coarsening of dendrite arms. By this model,the solid-fraction evolution of the globulitic dendritic can be calculated,the solid-fraction evolution of the star dendritic can also be calculated accurately. So this model can be used more widely.7. On the basis of simulation of grain structure formation in solidification of superalloy K4169 cylinder ingots,The grain structure features of superalloy K4169 blades under conventional investment castings and optimal refining processing were computed. The visualization of grain nucleation and...