Low temperature powder injection molding of iron micro-nano powder mixture

The low temperature powder injection molding (PIM) of the Fe micro-nano powder feedstock using a low melting binder was investigated in terms of the effects of nano powder on the molding property and the microstructural development during sintering. The feedstock consisted of 66 vol.% powder and 34 vol.% paraffin-wax binder in which the powder composition was 75 vol.% Fe micro powder (4 pm in average size) and 25 vol.% nano powder (100 nm). Injection molding was conducted under the conditions of 70 degrees C and 4 MPa. For comparison study, the micro powder feedstock was prepared with the same conditions of solid powder loading and binder composition. It was found that the presence of nano powders in the feedstock effectively suppressed some drawbacks such as powder-binder disintegration, binder extraction and collapse of powders by capillary effect of liquid binder during mixing and molding. The debound part maintained uniform and sound surface structure due to strong networks between the micro powders by enhanced sintering effect of nano powders during the debinding process. The PIMed gear underwent isotropic shrinkage in reaching near full densification during sintering while the micro grains did not grow due to the inhibition effect of the nano powders on the boundary migration of micro grains. Conclusively, the use of micro-nano powder feedstock might provide a potential application for processing the PIMed parts with full density and fine microstructure. (C) 2012 Elsevier B.V. All rights reserved.