Controlling Particle/Metal Interactions in Metal Matrix Composites During Solidification: The Role of Melt Viscosity and Cooling Rate

The homogenous dispersion of particles in a metal matrix is of critical importance to the design and manufacturing of particle-reinforced metal matrix composites (MMCs). This work studied the effects of increasing melt viscosity via microalloying and increasing cooling rate on the dispersion of particles in an aluminum-based MMC. A CALculation of PHAse Diagrams (CALPHAD)-based viscosity model was developed for the Al-Ni binary system. This viscosity model was coupled with a particle-capture model to explore particle/metal interactions during solidification. Three composites (Al + TiC_p) with and without Ni were cast at different cooling rates. The first composite without Ni cast at a lower cooling rate showed macro-segregation and agglomeration of TiC_p along the grain boundaries. The second composite without Ni cast at a higher cooling rate exhibited grain refinement and reduced macro-segregation of TiC_p. The third composite alloyed with 1 wt pct Ni and cast at the same higher cooling rate had an improved distribution, and particles > 2 µm in size were captured in the grains. The composite with 1 wt pct Ni had a 45 pct higher melt viscosity and a 31 pct lower critical velocity for capture of TiC_p, demonstrating a synergetic effect of increasing viscosity and cooling rate on improving particle dispersion in MMCs.