Study and Suppression of the Microstructural Anisotropy Generated During the Consolidation of a Carbonyl Iron Powder by
- PDF / 2,153,743 Bytes
- 7 Pages / 593.972 x 792 pts Page_size
- 37 Downloads / 164 Views
DUCTION
IN the last decade, powder consolidation methods using electric current and applied external pressure have been widely investigated due to their possibility of sintering a large range of materials, including ceramics, metals, and composites, in short processing times and few processing steps, with reasonably high densities and avoiding undesirable grain growths.[1–5] In addition, the influence of the sintering parameters on the quality and mechanical properties of final iron-based consolidated materials has been extensively studied.[6–8] In this framework, the field-assisted hot pressing (FAHP) technique is situated, in which a high densification is performed by the simultaneous application of an uniaxial pressure and a low voltage and high alternate current to the sample.[9,10] This method produces a fast generation of internal heat by Joule effect and accelerates the diffusion among iron atoms, which increases the kinetics of sintering.[11,12] The heating rate and the obtained densification are high, leading to the final consolidated sample in around 20 minutes. The powders are poured into an assembly of graphite tools, composed of several spacers, a cylindrical die, and two cylindrical punches to transmit the load. One of the limitations found in the electric current-activated/assisted sintering techniques arises in applications where high purity of the final consolidated specimens is needed, since the set-up formed by the graphite tools could lead ANDREA GARCI´A-JUNCEDA, Research Associate, and LAURA ACEBO, Student, are with the IMDEA Materials Institute, Calle Eric Kandel 2, 28906 Getafe, Madrid, Spain. Contact e-mail: [email protected] JOSE´ MANUEL TORRALBA, Deputy Director, is with the IMDEA Materials Institute, and also with the Universidad Carlos III Madrid, Av. Universidad 30, 28911 Legane´s, Madrid, Spain. Manuscript submitted February 16, 2015. Article published online April 28, 2015 3192—VOLUME 46A, JULY 2015
to the introduction of carbon inside the sample during sintering at elevated temperatures and using high heating rates.[13–15] Therefore, the carbon introduction may be an undesirable effect in many applications where the presence of carbon and/or carbides in the consolidated material is detrimental to its properties. Thus, finding a way to decrease or even suppress, this contamination would be an important key issue for future processing routes of advanced novel sintered materials. This investigation aims to provide a better understanding of the existence of a carbon contamination coming from the graphite die and graphite punches typically used for the sintering by field-assisted activated sintering techniques. The paper focuses on the effect of carbon diffusion on the microstructure of the consolidated material. Moreover, the alternative of interposing a thin tungsten foil between the powders and the die/punches has been evaluated in order to reduce or avoid the carbon contamination.
II.
EXPERIMENTAL PROCEDURE
A spherical carbonyl iron powder supplied by ECKA Granules was employed in
Data Loading...
