Sintering behavior of bimodal iron nanopowder agglomerates

Abstract

The most important issue in the processing of nanoscale metal powders is whether the metal nanopowder can be fully consolidated into ultra‐fine‐ or nano‐grained powder metallurgy parts by pressureless sintering. This paper focuses on the sintering behavior of bimodal iron (Fe) nanopowder agglomerates by considering their microstructure and densification kinetics. During the sintering, bimodal Fe nanopowder compacts underwent discontinuous shrinkage behavior until they neared full density. Three contributions to the sintering mechanisms, asymmetric sintering, densification enhancement, and grain growth inhibition, are presented in relation to the effect of bimodal nanopowder structure. Smaller nanoparticles in the bimodal nanopowders, which are predominantly present at the boundaries and interstitial spaces of larger nanoparticles, are responsible for the three mechanisms stated above. This result is strongly supported by the apparent activation energy values ranging from 48.2 to 90.6 kJ/mol, which correspond to the energy for grain‐boundary diffusion in Fe. The experimental results of this study show that bimodal nanopowder agglomerates can be used to produce full density nano‐grained powder metallurgical parts by pressureless sintering.

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

“…The values obtained appear to be in agreement with the activation energy of the grain-boundary self-diffusion of pure iron, which is in the range of 53 to 80 kJ/mol. [23] Song et al [20] also observed similar activation energy values while studying the sintering behavior of bimodal iron nanopowder agglomerates.…”

“…Sintering kinetics under non-isothermal conditions is more correct than under isothermal conditions. [20] Densification also occurs during the initial stages of the heating process, and therefore, it is difficult to determine whether changes occur during heating or isothermal holding. [21] To investigate the densification kinetics and the dominant mechanism, the non-isothermal sintering was thus analyzed.…”

Analysis of Iron Oxide Reduction Kinetics in the Nanometric Scale Using Hydrogen

“…There are different isoconversional methods to evaluate E at different degrees of conversion, α. The Ozawa, Flynn and Wall method uses a plot of log β verses 1 T plot whose slope gives E for a particular α [13]. There are other methods like the Friedman method and the nonlinear Vyazovkin method which have their own set of advantages or disadvantages [14,15].…”

“…The use of metal nanopowder instead of the conventional micrometre-sized powder for the powder metallurgical process route in order to manufacture near fully dense material has been of great interest for high performance applications [1]. The use of nanopowder however reduces the green density of conventionally die-pressed compacts owing to poor compressibility.…”

“…Plots of ln β T 2 vs 1. T for different degree of conversion of oxide film and heating rates for Fe nanopowder of size ranges (a) 40-60 and (b) 60-80 nm, respectively.…”