Behavior of Carbon and Oxygen during Sintering Process in Fe-Ni Alloy Compacts Made by Injection Molding

摘要

The effect of carbon(C) addition on sintering behavior of Fe-4mass%Ni alloy compacts shaped by metal injection molding (MIM) was investigated, and the role of carbon in the sintering process was examined. The specimens were made of carbonyl Fe(5.0 μm, 0.05mass%C, 0.2mass%O), carbonyl Ni(2.0 μm) and additional C powder. The amount of C addition was varied between 0g and 0.8g per 100g of Fe and 4mass%Ni mixed powder. The compacts were debound in air at temperatures ranging from 503 to 553K for 7.2ks, and were sintered in a reduced pressure of 1Pa at 1523K for 7.2ks. It was found that there exists a critical debinding temperature (T_d~c) above which oxides are formed but below which no oxide is formed in sintered compacts. T_d~c depends on the carbon(C) and oxygen(O) contents of debound compacts, and T_d~c becomes higher with increasing in C addition. The relationships between the C and O contents of debound compacts versus the C and O contents of sintered compacts were analyzed by introducing a parameter Δ C_d (≡ C_d-aO_d) which represents the stoichiometric ratio of C and O contents(C_d and O_d, respectively) of debound compacts. The obtained results showed that the reaction (M × O + C → xM + CO (M=Fe,Ni)) is dominant for reducing metal oxides during sintering process. In the case that debinding temperature (T_d) is lower than T_d~c, the relative densities of sintered compacts were almost constant (approximately 95%) regardless of amount of C addition.