Effect of surface oxide films on the properties of pulse electric-current sintered metal powders
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10/7/03
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Effect of Surface Oxide Films on the Properties of Pulse Electric-Current Sintered Metal Powders GUOQIANG XIE, OSAMU OHASHI, NORIO YAMAGUCHI, and AIRU WANG Metallic powders with various thermodynamic stability oxide films (Ag, Cu, and Al powders) were sintered using a pulse electric-current sintering (PECS) process. Behavior of oxide films at powder surfaces and their effect on the sintering properties were investigated. The results showed that the sintering properties of metallic powders in the PECS process were subject to the thermodynamic stability of oxide films at particles surfaces. The oxide films at Ag powder surfaces are decomposed during sintering with the contact region between the particles being metal/metal bond. The oxide films at Cu powder surfaces are mainly broken via loading pressure at a low sintering temperature. At a high sintering temperature, they are mainly dissolved in the parent metal, and the contact regions turn into the direct metal/metal bonding. Excellent sintering properties can be received. The oxide films at Al powder surfaces are very stable, and cannot be decomposed and dissolved, but broken by plastic deformation of particles under loading pressure at experimental temperatures. The interface between particles is partially bonded via the direct metal/metal bonding making it difficult to achieve good sintered properties.
I. INTRODUCTION
RECENTLY, pulse electric-current sintering (PECS), also called spark plasma sintering[1,2] or plasma-activated sintering[3,4] by some researchers, has received much attention as one of the most advanced materials processing. Main advantages of PECS compared to other sintering methods such as hot pressing and hot isostatic pressing processes are local high-temperature generation at the created contact, rapid heating, and consolidation.[1–7] In the PECS process, pulse electric current flows directly throughout the sintered materials and mold, and a very high heating efficiency is offered. It can easily sinter a high-quality compact that is carried out at a lower sintering temperature and in a shorter time than conventional processes, even to those materials that are very difficult to be sintered by other processes.[6–10] However, the mechanisms surrounding cleaning at powder particle surfaces, the acceleration of sintering during PECS, are not established. It has been indicated that the sintering mechanism is dictated by the presence of the oxide layer at powder particle surfaces for the sintering of metals, and the electrical and mechanical properties of powder compacts are sensitive to powder particle surfaces characteristics.[11,12] It is worth understanding the effect of surface oxide films of metallic powder on the properties of the specimens sintered via PECS process. According to the thermodynamic stability of oxide films at metal particles surfaces, three types have been summarized.[11,13,14] (1) Decomposition type (the first group of GUOQIANG XIE, formerly Graduate Student, Graduate School of Science and Techno
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