Manufacture and characterization of Cu-Zn-aL shape memory foams

PIERRE ARNEODO LAROCHETTE; BRENDRA WEISS; GRACIELA BERTOLINO; ENRIQUE CASTRODEZA; ALBERTO BARUJ; HORACIO E TROIANI

Saint-Petersburg

Simposio; 9th European Symposium on Martensitic Transformations ESOMAT 2012; 2012

ESOMAT

The low cost Cu-Zn-Al foams present, in specific composition ranges, good pseudo-elastic properties associated with interesting damping capacities, which establish these materials as attractive from the point of view of structural applications.For this work the possibility of manufacturing Cu-Zn-Al foams with compositions in the pseudo-elastic range by using two different synthesis methods has been studied. The purpose of this study was to determine the quality of each synthesis method remembering that small departures in local chemical composition would result in strong variations in the martensitic transformation temperature, Ms.The foams where manufactured by infiltrating the molten alloys with SiO 2 small spheres under pressure in two different ways. In process A the alloys were molten by using a resistive furnace, while in process B the alloys were molten in an inductive furnace. In both cases, the alloy was molten in an open crucible and the SiO2 spheres were infiltrated while the alloy was in the molten state. Afterwards the SiO2 spheres were removed by immersingthe material in a solution of water and hydrofluoric acid. As a consequence, we obtained polycrystalline foams with grains in the millimeter range and a 3 mm pore size, in accordance with the size of the SiO2 spheres used.The paper details both the local physico-chemical and mechanical characterization of the foams synthesized with the two different methods. Strong differences were found in the transformation profile and mechanical behavior between these the materials. This fact is due to two factors. In first place, in the case of the inductive furnace the melting time is shorter. Then, in the inductive process there is a lower zinc loss during alloy preparation incomparison to the resistive process. And second, during inductive melting there is a strong stirring of the molten alloy, which results in better homogeneity. The main conclusion is that the correct method to synthesize Cu-Zn-Al foams is the one which uses the inductive furnace.Additionally, the pseudo-elastic behaviors of foams produced with both methods were investigated at different temperatures. The temperature dependence of the transformation stress is lower than 0.3 MPa/K, while this value is 2.7 MPa/K for policrystals of the same composition.