Cupping tests of porous composite Cu-Al2O3
Aleksander Cyunczyk, Jan Sieniawski Politechnika Rzeszowska, Katedra Materiałoznawstwa, ul. Pola 2, 35-959 Rzeszów
Annals 3 No. 8, 2003 pages 392-396
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abstract It is well-known that mechanical properties, especially plasticity of porous metals nad alloys is strongly dependent not only on the volume fraction of porosity but also upon a pore geometry (shape, size and distribution of pores). Sintered materials are in many respects similar to cast iron materials, since the graphite and pores cinstitute internal notches. It is commonly known that the notching effect is very high in grey cast iron with the grphite lamellae and mild in spheroidal cast iron with the spheroidal graphite forms. So, for the sake of the mechanical properties of porous bodies, a change from irregular to spheroidal shape of pores is desirable. In this paper a preliminary investigation upon a cold stamping of sintered porous bodies is described. Dispersion strengthened Cu-Al2O3 composite was the object of an experimental. Elemental powders of copper and alumina were used as starting materials. Composite powder: copper + 1vol.% alumina was prepared by mechanical alloying (MA). A nontraditional variant of MA which is founded in repetition of powders pressing and compact filing was applied. This technique is described in the earlier work [3]. The MA-ed powder was cold pressed and then sintered. Two conditions for sintering were applied namely free sintering and sintering under inner pressure. During sintering under inner pressure the energy of compressed gas in closed pores is utilized for activation of sintering and alteration of pore shape from irregular to spheroidal shape [4-6]. Disk samples of 60 mm diameter and 1÷2 mm in thickness were obtained. Porosity of sintered samples was closed within the range of 10÷23%. Samples were stamped incupping test attachment (Fig. 2). The results are collected at Table 1. The force of stamping was recorded (Fig. 3). A limiting porosity, above which the correct drawpiece is not obtained, is greater for samples sintered under inner pressure than for samples sintered free. So, the spheroidization of pores (Fig. 4) during sintering under inner pressure is a cause of increase the plasticity of sintered composite. In both cases this limiting porosity rises with decreasing of the sample thickness. The force of stamping slightly depends on the density of samples (Fig. 5). Key words: metal matrix composites, porous body, shape of pores, cupping test