Macrosegregation and sedimentation in liquid phase sintering: Specific studies in the nickel-tungsten system and iron-copper system

Based on experimental results, a macrosegregation model has been proposed to explain sedimentation occurring in liquid phase sintering (LPS).; Macrosegregation has been observed both in the sintering process of nickel-tungsten (Ni-W) alloys and iron-copper (Fe-Cu) alloys. The experimental results indicate that whether the mushy zone is located at the top or at the bottom of the sample, macrosegregation can occur if a nonuniform structure is formed during LPS. The initial particle settling or floating gives rise to the liquid composition gradient. Elimination of the gradient requires substantial time and is accompanied by a retreat of the mushy zone. At the same time, the mass in the mushy zone is transported to the liquid zone. If the initial settling does not happen, macrosegregation will not appear. But a "true" sedimentation can be observed. These two types of sedimentation were compared and the rates were quasi-quantitatively estimated.; A numerical simulation model has been developed to simulate the macrosegregation process. This calculation provided a further understanding of the sedimentation mechanisms.