The effect of nano-sized stainless steel powder addition on mechanical and physical properties of micropowder injection molded part

• Adding nano-size powder is led to an improvement in surface roughness.
• Strength, hardness and density increased using nano-size powder addition.
• Bimodal powders mixtures decreased injection, sintering temperature and shrinkage.
• Microparts with full density and fine microstructure has been fabricated.

Micropowder injection molding (μPIM) is a new technology that has potential in the mass production of microcomponents. A bulk material of nanoparticles possesses completely different properties from those of large-sized particles. The main objective of this study is to study the effects of nano-sized powder addition on the μPIM process of powder-polymer mixtures for the fabrication of miniature parts. The binder systems consist of polyethylene glycol (PEG), polymethyl methacrylate (PMMA), and stearic acid (SA) with different powder loading blended with powders. The results indicate that increasing the nanopowder content to 30 wt.% increased the powder loading and decreased the injection and sintering temperatures. The sintered parts had densities of 96% of the theoretical value. High physical and mechanical properties of the sintered specimen were achieved with the 30 wt.% nano-sized powder sintered at 1200 °C at a heating rate of 5 °C/min under vacuum atmosphere. A significant reduction of the surface roughness of the sintered parts using the nano–microhybrid powder (Sa = 0.365 μm) was observed compared with the sintered parts with only micropowder (Sa = 1.002 μm). Using nanopowders, the hardness also increased from 182 HV to 221 HV with a linear shrinkage of approximately 9%, which is less than that of the micropowders (18%).