J. M. Gallardo

Bio: J. M. Gallardo is an academic researcher from University of Seville. The author has contributed to research in topics: Sintering & Powder metallurgy. The author has an hindex of 12, co-authored 39 publications receiving 346 citations.

Structure and properties of attrition-milled aluminium powder

Abstract: Aluminium powder has been attrition milled in the presence of 1.5 wt% of a wax. The aim was to achieve a mechanically alloyed powder amenable to powder metallurgy processing. Changes in particle size and form, microstructure, hardness and other properties of powders with milling time has been studied. Under the experimental conditions employed, a process time of 10 h was selected for the mechanical alloying of Al powder. The powder milled in this way shows a Vickers microhardness (127 HV) more than six times higher than the starting powder (20 HV), a coarser particle size (mean particle size is doubled) and a better flowability.

Development of electric resistance sintering process for the fabrication of hard metals: Processing, microstructure and mechanical properties

Abstract: This work presents the development of the Electrical Resistance Sintering (ERS) process for the fabrication of hard metals. The compositions of the materials produced were WC with 6 and 10 wt% of Co. In addition to the specific characteristics of the technology, the characterization of the produced parts is presented and compared to materials obtained by conventional processes. The parts produced by ERS present densities comparable to the ones obtained by conventional methods. The microstructural comparison shows a considerable grain size reduction in the ERS materials which consequently brings a hardness increase. ERS materials show similar fracture toughness to conventional ones. The very fast sintering allows performing the process without any protective atmosphere, therefore making this process very attractive for the production of materials that need to be sintered under non-oxidising environments. The total duration of the cycle, including heating, holding time and cooling is few seconds. Finally, some considerations about the scale up and possible industrialization of the technology are explained.

Electrical conductivity of metal powder aggregates and sintered compacts

Abstract: New equations for computing the electrical conductivity of powder aggregates and sintered compacts are proposed. In both cases, the effective or apparent conductivity is a function of the bulk material conductivity, the porosity of the sample and the tap porosity of the starting powder. Additional parameters are required for powder aggregates, such as the conductivity of the oxide covering the particles, the thickness of the oxide layers and the ease of descaling them. The new equations are valid from zero porosity to the tap porosity. Links between the equations and the percolation conduction theory are stated. Measurements of electrical resistance on sintered compacts and powder aggregates subjected to different pressures were performed. The proposed equations have been validated with these data. The electrical conductivity of both sintered compacts and powder aggregates of aluminium, bronze, iron and nickel was determined and compared to the equation predictions, resulting in notably good agreement.

Mechanical Alloying And Milling

Abstract: Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.