There is no standard MIM process; thus, variations exist between vendors. The differences come from the many choices of powders, binders, tool design, processing cycles, equipment design and operation, impurities, and post-sintering treatments. Part geometry can also drive specialized processes. Property scatter is small within a MIM operation, often less than seen in forgings or castings. However, the differences in details at each MIM company leads to possibly large cross-industry scatter.
For example stainless steels can absorb nitrogen in sintering and this tends to increase strength, but also reduces ductility to half the value seen with hydrogen sintering. If slowly cooled, nitrogen in a stainless reacts to form a compound that leads to significant corrosion problems. Hence, depending on the processing atmosphere and final density there will be property differences; one vendor will have high strength and low corrosion resistance and another may have high ductility and good corrosion resistance.
The differences between MIM vendors generally are as follows:
- Little difference in hardness and bulk chemistry
- Small difference in yield strength, tensile strength, and ductility
- Potentially large differences in impact toughness, fracture toughness, corrosion resistance, and fatigue endurance strength.