Surface analysis of fine water-atomized iron powder and sintered material

摘要

Press and sinter is a core technology in powder metallurgy in which a metal powder is mixed with a lubricant and other additives and subsequently compacted at large mechanical pressures to create the desired shape. The component is then delubricated and finally sintered to strengthen the material. The end result of the sintering depends on both the physical properties of the powder such as particle size, morphology, and size distribution, as well as chemical properties like surface chemical composition and presence of surface oxides. In this study, the surface characteristics of 3 fractions of water-atomized iron powder, sieved to -20, -45, and -75 mu m, were investigated. This was done by using X-ray photoelectron spectroscopy, Auger electron spectroscopy, and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. The powder was sintered while performing thermogravimetric analysis at 1350 degrees C for 30 minutes in pure hydrogen. Results showed that powder of all 3 size fractions were mainly covered by a thin iron oxide layer but with some presence of submicron-sized oxide particulates. X-ray photoelectron spectroscopy and thermogravimetric analysis showed reasonable agreement on the oxide layer thickness, while a size dependence was found with an enrichment of oxide particulates on the finer powder fractions. Fracture surfaces of the sintered material were analyzed with X-ray photoelectron spectroscopy and scanning electron microscopy + energy-dispersive X-ray spectroscopy, which indicated that full reduction of all oxides was achieved. The sintering conditions were further related to the surface properties of the powder and its size fraction.