Papers by Author: I. Iturriza

Abstract: Powder compacts from two different commercial aluminium powder grades have been densified by direct hot extrusion. The extrusion runs have been carried out at 425 °C, with an extrusion ratio of 1:16 and a ram speed of 1.5 mm/s. Prior to extrusion, some green compacts were presintered (500 °C). The evolution of the extrusion load during the process and the hardness of the final products have been investigated. Additionally, microstructural characterization by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Electron Backscattered Diffraction (EBSD) was carried out in order to understand the softening-hardnening mechanisms taking place during the process. The obtained results evidence grain refinement. Additionally, inter-metallic precipitation, dynamic recovery and geometric dynamic recrystallization take place depending on the composition of the powder, the heat treatment before extrusion and the strain involved in the process.

Abstract: Ceramic materials exhibit very low fracture toughness, which limits their applications. Recently, metal-ceramic composites have been developed to achieve improvements in toughness. In this work, the fracture toughness of SiC-Cu based alloys cermets, obtained by reactive infiltration, was measured at room temperature using the single edge notched beam (SENB) method. Values up to 11 MPam1/2 were obtained; these values were compared with the fracture toughness of commercial materials. The results of fracture toughness were directly related with the amount of the infiltrated metallic phase. The fracture energy was calculated using values of KIC and Young Modulus obtained from four points bending tests. Differences on toughness values were related with porosity and type of fracture of the several systems. The microstructural analysis of the fracture surfaces was carried out by scanning electron microscopy. The role of different operating toughening mechanisms; such as crack deflection, bridging, branching, and energy dissipation through microcracking and/or microplasticity; has been examined.