Papers by Author: Mónica Campos

Abstract: Since low alloyed sintered steels were introduced in the market of the structural parts, we have followed the evolution of a material with poor mechanical properties and any uniformity (in the sense of reproducibility) to materials that today are produced with high reliability and performance. The working efficiency could be equivalent in many cases with the best wrought steel, and maintaining a good margin in terms of cost and competitively. In this paper a complete review of the topic is accomplished, from the early times when the first parts were made by plain iron or iron-carbon, going through the different alloying systems: Fe-Cu, Fe-P, Fe-Cu-Ni-Mo, and more recently Fe-Cr-Mo and Fe-Mn. The development in processing routes has been considered too. The main milestones in the field of new alloying systems have been: 1) the introduction of Cu in 60-70’s, 2) the new complex systems with Cu-Ni-Mo in the 80’s and 3) the introduction of alloying elements with high oxygen affinity (in the late 90’s). Regarding the milestones in processing could be considered: 1) the development of new mixing procedures, 2) the warm compaction and high velocity compaction, 3) the improvements in sintering control and high temperature sintering. Several decades of research and innovation, acting on the processing system (mixing, pressing, sintering, post-sintering operations,…) and on the alloying system (from the earliest times with plain iron to complex systems used today), has allowed us to have a highly competitive materials, in terms of performance, and processes in terms of cost. The future is still open to new developments.

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: The efforts to increase the potential PM market [makes necessary to accept new challenges to develop new products. To address this question, we can consider modifying the pores system or the material composition and at same time, the cost of the alloying elements and the compromise between strength, tolerances and cost. The present study examines the sintering behavior and effect of manganese addition, both mechanically-blended and mechanically alloyed, on Cr-Mo low alloyed steels to enhance the mechanical properties. Mn sublimation during sintering results in some specific phenomena to occur which facilitate the sintering of alloying elements with high oxygen affinity. To benefit from the Mn sublimation effects, small Mn particles must be homogenously added in order to increase the specific surface available to sublimate. First, the milling time is optimized to attain a master alloy with 50% of Mn that is diluted in Fe-1.5Cr-0.2Mo water atomized prealloyed powder by normal mixing. These mixtures were pressed to a green density of 7.1 g/cm3 and sintered at 1120 °C in 90N2-10H2 atmosphere. The resulting mechanical properties and the microstructures are discussed considering the high energy stored in the master alloy which favors the mass transport mechanism during sintering.