THEORETICAL ANALYSIS ON THE MOVEMENT BEHAVIOR OF PARTICLES IN METAL MELT IN CENTRIFUGAL FIELD

A theoretical model of movement behavior of second phase particles in metal melt in centrifugal field was set up. The factors affecting the movement behavior of the particle were analyzed with this model. The results show that the distance and velocity of the particle moving from inside to outside increase with time in an exponential law. The bigger the particle diameter, the higher the particle density,and the faster the rotation speed of mold, then the longer the distance of particle movement will be. The phenomenon that particle runs after particle exists because of not only the difference of particle diameter but also the difference of particle density during the transport, which is the main reason that particles collide and accumulate and big particles or particles with big density segregate to the specimen outside. To reduce the pursuit, collision, and accumulation of particles during particles movement, it is very important to use the particles with the same diameter and composition. The distance between two particles whose initial positions in the radial direction are different increases gradually with time. For some particles whose space length is the same at a radial straight line, the distances between any two near particles are still equal after particles move for a moment though it is longer than that at the initial position. The gradient distribution of particles in the specimen is induced by the sedimentation of particles from outside to inside the specimen, the increase of viscosity of the metal melt with the temperature decreasing, and the solidification of the metal melt.