抄録
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.
