Nonuniform Sintering Shrinkage of Stainless Steel Powder Compacts Prepared by Metal Injection Molding

The authors have developed an “in-situ monitoring system of sintering shrinkage” using digital image processing, and have applied it to the measurements of the nonuniform and anisotropic sintering shrinkage of powder compacts prepared by metal injection molding (MIM) on a non-contact and real time basis. In the present study, the regional distribution of nonuniform shrinkages in two kinds of stainless steel (SUS304) powder compacts prepared by MIM were determined. The nonuniform shirinkages caused by the density inhomogeneities due to local temperature differences within the sample, by gravity effect of the sample, and by frictional restraint against free dilatation were confirmed. The nonuniform shrinkage caused by the density inhomogeneities due to local temperature differences has been found to take place in the early stage of sintering, where the thermal conductivity of compact is small because of large porosity and the shrinkage rate increases sharply with time, but it attenuates reversely in the final stage. The rate of the nonuniform deformation by constant load, i.e. by the gravitational loading, is proportional to the shrinkage rate during sintering. These effects will concurrently operate in the nonuniform sintering of complex-shaped MIM compacts.