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

Abstract

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 μm, 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°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.

Effect of Nanopowder Addition on the Sintering of Water-Atomized Iron Powder

“…In addition to the iron-oxide layer, with a thickness of approximately 7 nm, the micron-sized powder used in this study was to a small extent (< 5 pct) dotted with oxide particulate features sized up to 100 nm and rich in strong oxide formers such as Cr and Mn. [17] These oxide particulates were reduced above 1100°C when sintered in pure hydrogen. The fracture surface of the compact sintered at 1350°C revealed dimples, which were this devoid of any oxide particles.…”

“…This reduction of oxides was due to the high temperature applied for the pure hydrogen atmosphere. [17] The role played by nanopowder in the sintering process was thus mainly observed at temperatures between 500°C and 700°C. Nanopowder present in the inter-particle spaces and at the boundaries appeared to be sintered.…”

A Cold-Pressing Method Combining Axial and Shear Flow of Powder Compaction to Produce High-Density Iron Parts

“…The preform is made from water atomized pure iron powder PZhV2.160.2 powder (JSC Sulinsky Metallurguchesky Zavod, Krasny Sulin, Russia), which was produced under license and the analog of the widespread WPL200 powder [66,67] produced by Mannesmann Demag (Renningen, Germany). The chemical composition of the powder presented in Table 1.…”

Oxide reduction and oxygen removal in water-atomized iron powder: a kinetic study

“…As a consequence, oxides in PM material systems have been studied intensively for several decades. Recent investigations on water-atomized powder grades, the work-horse of the PM industry, have utilized a range of analysis methods for this purpose, detailing the physical and chemical properties of various oxides by thermogravimetric analysis (TGA) [3][4][5], TGA coupled with mass spectrometry (MS) [6,7], and surface analytical techniques like X-ray photoelectron spectroscopy (XPS) [5,[8][9][10][11], and Auger electron spectroscopy (AES) [5,9,12].…”

“…While the majority of the previous studies on water-atomized grades have been focused on the details of the thermodynamically stable oxides, the less stable surface iron oxide layer is less studied. Despite the small thickness of the oxide layer, owing to the large specific surface area of water-atomized powder, it still accounts for accounts for 30-50% of the total oxygen content in the powder, depending on particle size distribution, alloying elements, powder manufacturing and further storage and handling [5,8]. Consequently, a large amount of oxygen is readily available for oxygen transfer to stable oxide-forming elements if removal of oxygen released from the reduction of the iron oxide is not sufficient.…”