Sintering process sketch

Consequently, both the geometry and the density of sources and sinks for the sintering reaction are continually changing. When we view the entire sintering process in all its complexity, we can readily understand that a complete quantitative treatment is virtually impossible [17]. Therefore, in the following, we shall simply discuss the concepts and sketch out the equations necessary for a quantitative analysis. 

Three different trajectories in reaction sintering are sketched in Fig. 11.54, depending on the relative rates of densification and reaction. When the reaction rate is much faster than the densification rate (curve A), the reaction occurs predominantly before any significant densification, and thus, densification must be achieved for a microstructure consisting of the fully reacted powder. Curve C shows the trajectory when the reaction rate is much slower than the densification rate, and in this case, densification occurs without any significant reaction, so the reaction process must be carried out in a fully dense microstructure. Curve B represents the trajectory for a system where the reaction rate is comparable to the densification rate. 

Figure 7.1 sketches a sintering process. During compaction, material diffuses to the contact area between the particles, driven by the energy gained in reducing the surface. The contact areas round off and become larger. One consequence of this process is that the component shrinks by as much as 30% to 40%. ... 

Figure 11.54 Sketch showing three different processing trajectories in reaction sintering. Curve A is the trajectory for a system in which the reaction rate is much faster than the densification rate curve B is for a system where the reaction rate and densification rate are of roughly the same magnitude for the system following trajectory C, the densification rate is much faster than the reaction rate. (From Ref. 90.)...

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