Medium-Frequency Electrical Resistance Sintering of Oxidized C.P. Iron Powder

Abstract

Commercially pure (C.P.) iron powders with a deliberate high degree of oxidation were consolidated by medium-frequency electrical resistance sintering (MF-ERS). This is a consolidation technique where pressure, and heat coming from a low-voltage and high-intensity electrical current, are simultaneously applied to a powder mass. In this work, the achieved densification rate is interpreted according to a qualitative microscopic model, based on the compacts global porosity and electrical resistance evolution. The effect of current intensity and sintering time on compacts was studied on the basis of micrographs revealing the porosity distribution inside the sintered compact. The microstructural characteristics of compacts consolidated by the traditional cold-press and furnace-sinter powder metallurgy route are compared with results of MF-ERS consolidation. The goodness of MF-ERS versus the problems of conventional sintering when working with oxidized powders is analyzed. The electrical consolidation can obtain higher densifications than the traditional route under non-reducing atmospheres.

Nickel Porous Compacts Obtained by Medium-Frequency Electrical Resistance Sintering

“…These intensities, normalized with the compact cross-section, represent current densities of 5.31, 7.07 and 8.84 kA/cm 2 . These processing conditions were sufficient to achieve high densities in MF-ERS experiments with iron powder [8]. The 3 g of powder mass used in the experiments made the compact reach a height/diameter aspect ratio close to 1/2.…”

“…Comparing the ERS technique with the conventional powder metallurgy (P/M) route of cold-pressing and furnace sintering, three aspects are noteworthy: (i) the high densification rates achieved with the ERS at low pressures (around 100 MPa), (ii) the very short processing times (around 1-2 s), and (iii) the possibility of not using protective atmospheres, as a consequence of (ii). However, the usual non-homogeneous temperature distribution, inside the compacts, during ERS (or a similar technique) makes it difficult to achieve a homogeneous microstructure (and isotropic properties) throughout the compact [8][9][10][11]. In addition, finding a suitable material that provides acceptable cost and durability for the dies is also a problem [12].…”

Influence of Processing Parameters on the Conduct of Electrical Resistance Sintering of Iron Powders

“…The main disadvantages of the ERS technique arise from operational difficulties (incomplete knowledge of how certain parameters influence the process) and the problem of achieving a homogeneous temperature distribution in the powder mass [18]. Some of the authors of this paper have studied this process, both from the experimental and theoretical points of view [19][20][21]. One of the important problems of the ERS technique refers to the durability of the ceramic dies, which was studied in [22].…”

Amorphous Al-Ti Powders Prepared by Mechanical Alloying and Consolidated by Electrical Resistance Sintering

“…These techniques are a type of hot pressing in which the powder itself generates heat due to the Joule effect, and are called "electrical resistance sintering under pressure". However, these methods are still today of great interest [13,14], coexisting with the traditional powder metallurgy (PM) route of cold pressing and furnace sintering. The main advantages are the achievement of very high densities with moderate or low pressures (around 100 MPa), the need of extraordinarily short sintering times (about one second) and the option of sintering in air.…”