Materials and Technologies

Abstract: In this paper we try to summarize the research activities of the PM group in the University Carlos III of Madrid. This research group is highly devoted to PM activities covering different fields (both under the point of view of the materials and the processes). In the PM lab powders can be produced by spray pyrolysis, mechanical alloying and water/gas atomization. These powders can be processed by pressing and sintering, powder injection moulding, isostatic pressing,… Sintering facilities cover vacuum and gas controlled sintering. Regarding the materials, in the group we have different research lines covering low alloyed steels, stainless steels, HSS, ferrites, metal matrix composite (Al and Fe base), Ti, intermetallics, ceramics with functional and structural propierties, … In this paper we describe slightly some of the recent developments produced in the group which is not exhaustive (are there a few more) but representative about we are doing at present.

Abstract: This paper is a review of the marvelous development of mathematical and computer models that describe the fundamentals of microstructure evolution during the solidification of cast alloys, from the 1966 seminal paper by Oldfield, the first to attempt computational modeling of microstructure evolution during solidification, to the current prediction of mechanical properties. The latest analytical models for irregular eutectics such as cast iron, as well as numerical models with microstructure output, to include cellular automaton, will be discussed. Phase field models will not be discussed because of their inapplicability to casting solidification at the present time.

Abstract: The Volume-CAD System Research Program aims at developing a core technology for data integration of computerized design, analysis, manufacturing, and testing processes. The potential applications of the Volume-CAD environment cover a large area of engineering and biomedical design. In this paper, we shall mainly focus on the VCAD-based software for the structural analysis and the simulation of casting processes.

Abstract: This work concerns the study of the fatigue properties of A319, A 356 and A357 Aluminum alloys, produced by means of permament mould casting, sand casting and loast foam. Smooth plane or cylindrical samples were cut out from supension arms, engine blocks and cylinder heads and then they were subjected to axial fatigue testing at room temperature. Some castings were subjected to LHIP (Liquid Hot Isostatic Pressing) and also the effect of this process has been evaluated regarding the improvement of fatigue properties. Optical microscopy and scanning electron microscopy (SEM) were used to document the elimination of porosity after LHIP and to show the different nucleation sites of fatigue cracks on the fracture surfaces in no-LHIP and LHIP conditions.

Abstract: Some of new severe plastic deformation processes as equal channel angular extrusion, and strip shearing are presented as very efficient techniques for grain refinement. Channel geometry, contact friction, strain rate and multi-pass processing versus microstructure and mechanical properties are shown.

Abstract: During the last 60 years, tremendous developments have been in wire rod rolling. Finish rolling speeds in the order of 100 – 140 m/s are common and on line wire rod cooling practices, has made it possible to treat the wire rod directly in line in the mill instead of separate off line operations. New procedures for roll setting have been developed to cut the downtime in the mill, by presetting the stands in separate workshops an supply the entire rolling line with fast changing equipment. Much of the efforts have been directed to improve the productivity and the wire rod quality, but also to improve the working environment. In the 21:st century, the main challenge will be the global energy saving and environment protection, which in turn will require new trends in wire rod rolling and wire rod rolling research. The in line treatment will be applied for more steel grades, but the important savings must be solved at the interface between the steelmaking/continuous casting and the wire rod rolling. Hot charging as well as warm rolling will be employed in order to save energy. Their knowledge of the rolling processes will be improved by means of new methods for plastic analysis. New processes must be introduced, where the requirements from the rolling mills will direct the development. These are including casting of smaller billet sections, in order to minimize the mechanical work, and thus the consumption of electrical energy for conversion of the billets to wire rod. By the development of these technologies not only energy will be saved. Better wire rod surfaces can be obtained and the investment cost for new rolling mills will decrease. However the development of new knowledge and new processes requires funding on a level that is hard to expect, especially from the funding system which exists at present.

Abstract: It is now fairly well established that to achieve low values of the Paris exponent for the growth of fatigue cracks in PM steels, high values of fracture toughness are required. Fracture toughness is related to other measures of toughness, such as impact tests and the mechanical work that the material can absorb before fracturing. All of these are functions of the basic ductility of the material. A coherent picture of all these inter-relationships is presented.

Abstract: Consolidation of aluminium alloys by sintering present a main problem: the oxide layer that cover aluminium particles. Some alternatives are studied in this work as solution to the oxide layer problem during the sintering of series 2xxx aluminium alloys. One of these solutions is related to the addition of tin traces, and the other is the addition of a second alloy. Moreover, aluminium metal matrix composites are characterized by excellent properties as combination of properties which comes from the matrix and from the reinforcement. In the first part of this work is analyzed the influence of trace additions, and the last part of this study is focused to the analysis of one aluminium matrix composite as the influence of several quantities of reinforcement.

Abstract: It was studied the possibility to obtain cermets with nickel on alumina basis, using conventional methods such as cold pressing and sintering. γ transitional alumina was employed as oxide elemental, due to its OH- groups which have a positive effect to the press, by decreasing the friction forces. There were investigated the Al2O3-Ni cermets in the range where the concentration of the ceramic material is preponderant. Oxide and metallic admixtures were mixed in the powdered blend in order to study their influence on the properties of the cermets. These were characterized by measuring sintering density, hardness, bending strength and fracture toughness. The values of the characteristics are comparable to those reported in literature for non-conventional energetic methods: the sintered density up to 98%TD; the Rockwell hardness up to 40HRC; the bending strength up to 352MPa and the fracture toughness up to 4MPam0.5, function of their composition. The fracture has a mixed character, it is fragile-ductile.