![]() ![]() Metals and metallic alloys with these characteristics respond to the tension applied by sliding the plates and this process can be reversible unlikely most of the metals do not show this transformation. Its product generates invariant tension in the lattice, producing defects such as twinned plates, stack defects and/or dislocations 23,24. The martensitic transformation occurs by shearing, also called invariant tension of the plane. These can be described starting from orthorhombic unit cells and showing some distortion (monoclinic distortion) when compared to the perfect pilling up of the original phase 22. Then each one of the 6 groups has 2 opposite directions itself and 2 equivalents because the variants are twinned, and 24 variants of martensitic structure single crystal are formed 20,21. It is the case of the transformation from the original b phase (DO 3) to 18R 1 martensite (b'). With stereographic projection 6 groups of these planes were found, each one with 4 variants or clusters around each plane. For instance, beginning with the plane present in the original phase, habitual planes found in the martensitic phase can be calculated. Starting from original b phase single crystal (body-centered cubic crystalline system) a martensitic phase can be obtained by cooling, and 24 martensite variants can be formed to self-accommodating. Martensitic structures can also be originated from the b phase structure. Considering our interest in shape memory copper-based alloys 17-19, simultaneously to the b phase Cu-Zn-Al preparation, martensitic Cu-Zn-Al single crystals were also obtained. Single crystals were orientated in the (111), (110) and (100) crystallographic planes 12,14, using the Laüe back-reflection method 15,16. Our studies began with an easier crystallographic system, a single crystal b phase Cu-Zn-Al alloy, which belongs to the DO 3 ordered structure. To go deeper on electrochemical studies of these copper-based alloys it was decided to study orientated single crystal of these materials.ĭue to the difficulties to buy single crystals of copper-based alloys with a desired composition, a furnace previously described 11 was modified and constructed 12 in our laboratories to obtain single crystals based on the Bridgman's method 13. The electrochemical response obtained with such polycrystalline materials is determined by the contribution of all crystalline planes present on the electrode surface and exposed to the solution. For Cu-Al-Ag alloys, depending on the media and silver or aluminum concentration, the electrochemical behavior was influenced by silver 1-3,6,8 or even controlled by aluminum 4,7,10. Many results obtained for these metallic alloys were strongly influenced by copper, the majority element. These studies were conducted only with mono- or polyphasic polycrystalline alloys in the following metallurgical conditions: as cast, annealed, quenched or submitted to other heat treatments. The electrochemical behavior of copper-based alloys and their pure elements has been studied for many years by the authors in alkaline, salt and acid solutions 1-10. Keywords: single crystal orientation copper-based alloy Laüe back-reflection method. It was observed that the tension stress was applied along the direction. This single crystal was oriented using the Laüe back-reflection method to give surfaces with the following oriented crystallographic planes: (010), (120) and (130). ![]() The single crystal was submitted to 8 tons of tension (stress) along the longitudinal direction to reduce the number of variants and facilitate the surface orientation according to the desired plane. The martensitic phase (monoclinic) can present up to 24 variants, and orienting the surface according to a certain plane is a very hard task. ![]() Ciencia dels Materials y Enginyeria Metal-lúrgica, Universitat de Barcelona, C/ Martí i Franqués 1, E-08028 Barcelona, SpainĪ martensitic single crystal Cu-23.95Zn-3.62(wt.%)Al alloy was obtained melting pure Cu, Zn and Al using Bridgman's method. IICPT Thermal spray Center, Materials Engineering, Dept. IDepartamento de Físico-Química, Instituto de Química, Universidade Estadual Paulista, CP 355, 14801-970 Araraquara - SP, Brasil Uíslei Carlos Zambrano I Matildes Blanco I Nilso Barelli I Assis Vicente Benedetti I, * Javier Fernández II Laüe back-reflection method for crystallographic orientation of a martensitic Cu-Zn-Al single crystal of the monoclinic system
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