2016 Volume 57 Issue 3 Pages 257-262
The fractions of Al atoms at three kinds of crystallographic sites were determined in a Cu-15.5Al-4.0Ni (mass%) alloy before and after aging using powder X-ray analysis in order to clarify the effect of aging on the martensite start temperature, Ms. The ordering between first nearest neighbors (the B2 ordering) was almost finished even just after quenching, but the ordering between second nearest neighbors (the L21 ordering) was incomplete. The B2 type ordering occurs in advance of the L21 ordering in Cu-Al-Ni alloys as well as in Cu-Al-Zn alloys. The degree of L21 order increases from 0.699 to 0.844 during aging at 200°C for an hour. The increase in Ms during the aging is attributed to the L21 ordering in Cu-Al-Ni alloys.
