Effect of molecular interaction on the strength of green compacts

Modern approaches to calculating the strength of green compacts by van der Waals forces (σVW) are reviewed. Respective components (σVW) are calculated and green tensile strength (σtl.av) is experimentally determined for test powders of metals (Al, Zn, Cu, Ni, and Mo) and one nonmetal (FeSi). Comparison of σtl.av/σVW ratios shows that σtl.av and σVW are of one order for the atomized zinc powder, and σVW is greater than σtl.av for the atomized copper powder, though σtl.av is greater than σVW by two to three orders for most powders with irregular shape of particles. This difference can be attributed to the effect of shape and mechanical interlocking or seizure of particles when compacted. To predict the green strength, it is necessary to take into account both the shape of particles (or relative apparent density of the powder) and the forming temperature.