Student Information

3.  Sintering

In a typical sintering step, the green compact is placed on a mesh belt and moved slowly through the sintering furnace.  The temperature within the furnace rises slowly in the preheat zone until reaching the actual sintering temperature.  It remains essentially constant during the time at temperature, and proceeds into the cooling zone where the drop in part temperature is controlled (Figure 7).  The sintering temperature is kept below the melting point of the base metal.  Some of the alloying additives may melt, which results in liquid phase sintering.  Typically the furnace contains a protective atmosphere to prevent oxidation of the parts in the hot zone, and to help reduce oxides still present.

As the parts travel through the furnace, the temperature cycle results in changes in composition and microstructure.  In the preheat zone, the lubricant volatilizes, leaves the part as a vapor, and is carried away by the dynamic atmosphere flow.  In the hot zone metallurgical bonds develop between particles and solid state alloying takes place.  The part then moves through the cooling zone.  The microstructure developed during sintering determines the properties of the part.

Figure 7:  Sequence of Operations in a Sintering Furnace-Schematic: Source "Powder Metallurgy Science" Second Edition, R.M. German, MPIF.