PREDICTION OF SINTERED DENSITY FOR BIMODAL POWDER MIXTURES

Bimodal mixtures improve the green density of powder systems and are used in processes such as slip casting and powder injection molding. The packing density can be predicted with reasonable accuracy, but there is great uncertainty in the sintered density of a bimodal mixture. The large/small composition effect on packing density and sintered density is treated using the specific volume. For a given composition, the packing density is accurately predicted when four parameters are known: particle size ratio, packing density of the small powder, packing density of the large powder, and mixture homogeneity. Prediction of the sintered density is possible from knowledge of the densification of the large and small powders and mixture homogeneity. The model is applied to bimodal mixtures of molybdenum, stainless steel, iron, and alumina. Certain criteria must be satisfied by the constituent powders for a bimodal mixture to exhibit the highest sintered density. In many situations, the highest sintered density occurs at the 100 pct small powder composition.