日本金属学会誌

J. Japan Inst. Metals, Vol. 40, No. 12 (1976),
pp. 1208-1215

Microscopic Observation of γ' and α -Cr Duplex Precipitation in 40Cr-4Al-Ni Alloy

Shuichi Komatsu1, Masako Nakahashi1, Itaru Watanabe1 and Kazumi Shimotori1

1Metals and Ceramics Laboratory, Research and Development Center, Tokyo-Shibaura Electric Co., Ltd., Kawasaki

Abstract:

It had been found that 40Cr-4Al-Ni alloy showed extremely high age-hardenability. The hardness of this alloy, for example, was approximately 680 Hv after heat treatment at 700°C for 30 min. The age-hardenability was suggested to be derived from the duplex precipitation of Ni3Al type γ' and α -Cr phases. However, the morphology of the precipitated phases has not been clarified.
In the present work, the transmission electron microscopic observation was made on the specimens heat treated at various temperatures. It was found that γ' and α phases showed different morphologies in three temperature regions, below 500°C, 550∼700°C and 800∼900°C. In the region below 500°C only the α phase precipitated. The maximum age-hardenability was attained in the temperature region of 550∼700°C. In this region fine γ' particles precipitated in the matrix and then cellular precipitation started rapidly at the grain boundary. In the cellular precipitation region the α phase was observed in the shape of fine lamellar structure. The lamellar γ' phase precipitated at the interface between the α phase and the γ -matrix.
The characteristic formation of these three layers composed of α , γ' and γ -matrix phases seemed to correspond to the maximum hardness observed in this alloy. In the 800∼900°C region fine γ' particles were not detected in the matrix and the α phase changed to granular morphology in the cellular precipitation region. The precipitation behavior of the α , γ' duplex phases and its effect on the age-hardenability are discussed.


(Received 1976/02/6)

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