Microstructural characterization of dislocations in the high temperature phase (β 3 ) of CuAlNi shape memory alloys ML Nó 1 , A Ibarra 1 , J San Juan 2 1. Dpto de Física Aplicada II, Fac. de Ciencia y Tecnología, UPV/EHU, Apdo 644 Bilbao (Spain) 2. Dpto de Física de la Mat. Condensada, Fac. de Ciencia y Tecnología, UPV/EHU, Apdo 644 Bilbao (Spain) email contact of corresponding author maria.no@ehu.es Keywords: Dislocations, LACBED, weak beam Recent advances and developments for applying shape memory alloys (SMA) in micro devices have stimulated the characterization of the martensitic transformation at nano scale and in particular CuAlNi SMA micro and nano pillars show superelastic transformation under compression tests [1]. Moreover previous studies show that martensitic lathes not only are nucleated on martensite variants but they can be also nucleated on dislocations [2]. Consequently the knowledge of the distribution and the kind of dislocations in the high temperature phase (β phase) can be important. Two Cu-27.96Al-3.62Ni (%at) single-crystal alloys with different orientations have been treated at 1173K for 1800s, quenched in ice water, and aged for 4h at 453K. The martensitic transformation temperatures are under RT showing at Room Temperature (RT) the metastable β 3 phase (Fm-3m, L21 ordered structure, a=0.582nm [3]). TEM samples were prepared by electro-polishing and a TEM Philips CM200 with a super-twin lens has been used for their characterization. The dislocation lines have been determined by the traditional methods looking their projections under two beam conditions. However, for the b (Burgers vector) determination, the extinction conditions under g.b = 0 is not a good choice when samples have a high anisotropy [4], as in the case of CuAlNi alloys (A ≈ 13). In this situation we have used the large angle convergent beam electron diffraction (LACBED) method, which is an appropriate method to determine b [5-6] provided that dislocations are enough separated. Finally the weak beam method has been employed in order to determine the dissociation of dislocations, and this last result has been confirmed by the splitting of lines in the CBED method. Samples show straight dislocations characterized in a first step as edge dislocations. A detailed analysis of the dislocation microstructure shows that these straight dislocations take part of prismatic loops, on the {001} planes, partially destroyed during sample preparation. Only the loops on the (001) sample plane are conserved. Figure 1a shows one of these loops on the (001) plane (segments a,b,c,d) and two straight segments (e, f) coming from loops on planes (100) and (010). Due to their high anisotropy, the dislocations segments show extinctions for only one g.b condition and the LACBED method was also used to precisely determine the Burgers vectors direction and modulus. A LACBED micrograph is showed in Figure 1b as an example. The complete burgers vector analysis show that the loop abcd has b = -(1/2)[001] and segments e and f have b e = - (1/2)[100] and b f = (1/2)[010]. The weak beam method shows that segments of dislocations constituting loops are dissociated (Fig.1c) and the splitting of lines inside the CBED confirms this result (Fig.1d) although due to the resolution limit of the technique it is difficult to attribute the splitting to a stacking fault or to an APB. Finally a mechanism for the formation of these loops is proposed.