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Vol.44, No.3, 145 ~ 155, 2006
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| Title |
| Effect of Mo Addition on the High Temperature Oxidation & Hot Ductility of Fe-Ni-Co Kovar Alloy |
| 이기안 Kee Ahn Lee , 조창완 Chang Wan Cho , 성병근 Byung Gen Sung , 김병문 Byung Mun Kim , 김문철 Mun Chul Kim |
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| Abstract |
| The high-temperature oxidation behavior of two Fe-29%Ni-17%Co (Kovar) alloys with different Mo additions was investigated at temperatures ranging from 1190℃ to 1250℃ under an N2 + O2 environment. And then, the effect of surface oxidation and Mo addition on the hot ductility of the Fe-Ni-Co alloy has been studied. The oxidation weight gain increased with increasing temperature and increasing oxygen content in the N2 + O2 environment. The oxidation resistance of the Kovar alloy apparently improves with the addition of Mo. On the other hand, surface analysis using EPMA, ESCA, and XRD revealed that the oxide scale formed in these two alloys consisted mainly of three different external oxide layers (Co-based oxide, Fe2O3, (Fe, Ni)Fe2O4) as well as the internal oxide layer of NiO. Mo was found to be strongly segregated on the boundary between the internal and external oxidation layers and consequently believed to play an important role particularly in decreasing the thickness of the internal oxide layer. Regardless of the alloy composition, the formation of oxide layer was found to have minimized the hot ductility of the Kovar alloy significantly. Grain boundary micro-cracks in the internal oxide region were also noted following deformation due to high temperature, one of which acting as a notch that caused the poor hot workability of the oxidized specimen. The addition of Mo to the Kovar alloy could also retard the decrease in the hot ductility of the oxidized specimen through the prevention of notching due to internal oxidation. |
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| Key Words |
| Low thermal expansion, Kovar, High temperature oxidation, Hot ductility, Mo |
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