気孔球状化処理を施した焼結鉄のヤング率測定による気孔形状の評価

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The author reported previously that the Youngs modulus of sintered iron compacts measured by the resonance method was affected by the pore shape, rather than by the pore size and number. The purpose of this study is attempts to express quantitatively the effect of pore shape on Youngs modulus and evaluate the degree of spheroidizing of pores in sintered iron compacts added by alloying elements such as P and Si. The results are summarized as follows: Using the proposed pore shape factor, η, which is mainly based upon the Hashins elastic theory, the relation between Youngs modulus of compacts, E, and the porosity, s, can be simply and successfully expressed as E/E0=(1-ε)/(1 +ηε), where E0 is Youngs modulus of bulk material. In the case of sintered iron compacts, the value of η takes about 1 for the spherical shape of pores, and 2 to 3 for the pores with rounded edges. Thus, the value of η increases as the pore shape becomes irregular and angular. For a given amount of porosity, Youngs modulus of Fe-P compacts sintered above 1050°C (eutectic temperature of Fe-Fe3P) is higher than that of Fe compacts alone, which is due to the appearance of spheroidized pores by the liquid phase sintering. Addition of 3 wt%Si to atomized iron powders is somewhat effective on the spheroidization of pores as compared to that of 0.4 wt%P for the same sintering conditions, e.g. 1150°C×1hr. Youngs modulus of Fe-2.5%Si-0.3%P compact increases with increasing sintering temperature, and the elastic behavior of the specimen sintered at 1200°C for 1 hr is comparable with that of the carbonyl sintered iron, and the value of η of the former reaches nearly 1. Moreover, it was found that sintered iron compact treated by the gas sulfurizing shows a considerably spheroidized pore structure.
社団法人粉体粉末冶金協会の論文

著者

三浦秀士
九州大学工学部

気孔球状化処理を施した焼結鉄のヤング率測定による気孔形状の評価

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