Sintering of Powder Compacts

When we have compacted a powder to some shape, turning it into a useful part is, in principle, quite simple. All that should be necessary is to put the compact in a furnace for awhile, between 0.5 and 0.8 of its melting temperature, and hold it there for a few hours. Since elimination of internal surfaces means lowering the free energy of the system, diffusion should redistribute the atoms inside the powder compact, slowly trying to fill up the voids (pores). You could expect a final product that has some pores in it and in which the grain size has increased, in some cases significantly, compared to the initial particle size. Typically, if we start with a powder particle size of 1 µm or less, we might have a final grain size of 10 to sometimes 100 µm. Since there was no massive melting in the powder mix (we allow for some powder mixtures to have some liquid present during sintering) the compact retains its form, and the final shape is a shrunken version of the initial compact shape. For large parts we will need to guard against sagging during sintering and judicious support may have to be used.