DEFORMATION TWINNING IN A FACE-CENTERED ICOSAHEDRAL AL-CU-FE QUASI-CRYSTAL

We have determined the twinning mode in icosahedral Al65Cu23Fe12 deformed by high-temperature creep. The twinning elements K1, K2, eta1 and eta2 have been determined from electron diffraction experiments. Both of the invariant planes K1 and K2 were determined to be of the fivefold {1/0 0/1 0/0} type, and the two directions eta1 and eta2 were found to be midway between two twofold directions and of the [1/2 1/1 2/1] or [1/10 1/3 0/1] types. Considering the large amount of shear strain accommodated by this twinning and the large number of possible twin planes, a substantial amount of plastic deformation can be accommodated by deformation twinning in these materials.