Utilização do processo freeze-casting na obtenção de scaffolds de liga de memória de forma Cu-Al-Ni-Mn-Nb

Abstract

Shape memory alloys (SMAs) can recover their original shape after plastic deformation when exposed to either thermo mechanical or magnetic stimuli. These materials usually show interesting properties, including the shape memory effect and superelasticity. Porous SMAs can act as a two-phase composite, matching the properties of SMA and porous structure. Thus, it is possible to obtain materials showing low densities and distinct energy absorption capacities for use in damping systems. This work deals with the preparation of freeze-casted scaffolds using a Cu-11.29Al-3.1Ni-2.85Mn-0.345Nb (wt%) SMA, water as the freezing vehicle, citric acid and polyvinyl alcohol as dispersing and binding agents, respectively. The starting powder used in this study was initially obtained by spray forming and then separated into two groups according to their granulometry. After the stages of freezing the suspension and freeze-drying the ice crystals formed, the green bodies were sintered in an argon atmosphere at 980 °C for 6 h, and then quenched in the oven itself. The obtained scaffolds were examined by scanning electron microscopy (SEM), X-ray spectroscopy (EDS), X-ray diffraction (XRD), differential scanning calorimetry (DSC), X-ray microtomography (micro-CT), mercury intrusion porosimetry, and Archimedes tests. The starting material was also characterized by SEM, EDS, XRD, DSC, as well as helium gas picnometry and laser granulometry. The mechanical properties of the scaffolds were evaluated by dynamic mechanical analysis (DMA) and compression tests conducted at room temperature. Despite the low compressive strenght of the samples produced, due to only partial sintering between the particles, and no pore orientation, the use of freeze-casting proved to be an alternative route to produce porous Cu-Al-Ni based porous SMAs with good damping ability in high temperature applications.