The Effects of Aging on the Degree of Order in Cu-Al-Ni Shape Memory Alloys

Abstract

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, M s . The ordering between first nearest neighbors (the B2 ordering) was almost finished even just after quenching, but the ordering between second nearest neighbors (the L2 1 ordering) was incomplete. The B2 type ordering occurs in advance of the L2 1 ordering in Cu-Al-Ni alloys as well as in Cu-Al-Zn alloys. The degree of L2 1 order increases from 0.699 to 0.844 during aging at 200°C for an hour. The increase in M s during the aging is attributed to the L2 1 ordering in Cu-Al-Ni alloys.

Theoretical and Experimental Designs on Several Mechanical Properties of Cu–Al–Zn Shape Memory Alloys Used in the Processing Industry

“…Shape memory alloys can be classified into the following groups according to the nature of the chemical elements found in their composition: Alloys based on Ni–Ti [ 2 , 7 , 8 , 9 ]; Copper-based alloys (Cu–Al–Zn, Cu–Al–Ni) [ 10 , 11 , 12 , 13 ]; Ferrous alloys (Fe–Mn, Fe–Ni–C) [ 14 , 15 , 16 , 17 , 18 , 19 ]; Noble alloys (Au–Cd, Ag–Cd) [ 20 , 21 , 22 ]; ”Exotic” alloys (In–Te, In–Cd, V–Nb, etc) [ 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. …”