日本金属学会誌

J. Japan Inst. Metals, Vol. 56, No. 7 (1992),
pp. 828-832

Changes in Pore Microstructure of Iron Sintered Compacts by Diffusion-in of Foreign Elements

Tai-Whan Lim1 and Koji Hayashi1

1Institute of Industrial Science, The University of Tokyo, Tokyo

Abstract:

The pore microstructures in both the incompletely densified sintered compact of carbonyl iron powder near the interface of the diffusion couple of the sintered compact/Mo or Nb plate, etc., and the completely densified sintered compact of oxide-reduced iron powder (containing the oxide particles and no pores) into which carbon was diffused by heating in CH4 atmosphere, were investigated in order to verify the present authors' hypothesis that the incomplete or complete densification of iron fine powder sintered compact mainly depends on whether the equilibrium pressure (PCO) of CO gas which is generated by the reduction reaction of the oxide with impurity carbon and is trapped in closed pores, is higher or lower than the surface stress, i. e., the driving force for pore shrinkage.
The results obtained were as follows: (1) The closed pores in the carbonyl iron sintered compact did not disappear by diffusing-in of the elements like Mo which has no ability to decrease PCO, and did disappear by that of the elements like Nb which has ability to decrease PCO. (2) The diffusing-in of carbon into the oxide-reduced iron sintered compact resulted in the formation of pores around the oxide particles near the surface of the compact. (3) The above results as well as the results and considerations in the present authors' previous report could be said to all support the above hypothesis.


(Received 1992/03/10)

Keywords:

pore, carbonyl iron powder, diffusion couple, incomplete densification, complete densification, equilibrium pressure


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