Shigeaki Sugino1, Norihiko Nakanishi2 and Hiroyasu Mitani3
1Department of Metallurgy, Faculty of Engineering, University of Osaka Prefecture, Osaka
Effects of the Mn addition on the phase transformations of β Cu-Al alloys were studied by means of specific heat measurements and X-ray investigations. It was found that two types of martensite, β' and γ', were formed in Cu-11.8%Al-4%Mn alloy. Only β' martensite is observed in a quenched specimen, and both β' and γ' martensites are formed in a slowly cooled specimen. In the course of cooling the β phase, the occurrence of an ordering transformation, β → β1, resulted in an alteration in the concentration of the β phase. It is thought that the β' martensite is formed in the Al-poor β phase and the γ' in the Al-rich region. Several structures were supposed for the β1 phase which appeared in Cu-Al-Mn alloys.
The crystal structure of the γ' martensite formed in an alloy containing 12.5%Al and 4%Mn was determined to be orthorhombic with lattice parameters of a=4.45 Å, b=5.30 Å and c=4.24 Å.
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