Abstract Shape memory alloys are generally produced by casting processes and are subsequently homogenized. However, to obtain semifinished products on an industrial scale, the ingots from the casting process must be hot worked. In particular, final bar and sheet products can be obtained by hot rolling process. During intense hot work, surface oxidation of the material and microstructural changes may cause modifications to its original thermomechanical properties. In this sense, the present work aimed to study the correlation of the superelastic behavior in a Cu-Al-Be-Cr alloy before and after subjecting it to the hot rolling thermomechanical process. Abnormal grain growth was observed for a hot rolled sample with 30% reduction in initial alloy thickness. This abnormal growth in relation to non-rolled alloy caused an increase in phase transformation temperatures, a reduction in residual strain, a reduction in induction stress and an increase in alloy superelasticity.

RESUMO O conhecimento amplo do comportamento termomecânico das ligas com memória de forma (LMF) faz-se necessário para obtenção de ligas com elevada histerese térmica, o que torna possível eliminar a necessidade de meios criogênicos em muitas aplicações. Desta forma, os modelos matemáticos surgem como uma alternativa eficaz para descrição deste comportamento termomecânico. No presente trabalho foi desenvolvido um modelo matemático capaz de mensurar a deformação residual para uma liga Cu-Al-Be-Nb em função das variáveis: deformação, temperatura e taxa de deformação. Observa-se que os resultados obtidos por meio do modelo apresentam boa concordância quando comparado com os dados experimentais. Além disso, verificou-se que o modelo é capaz de prever as condições necessárias para se obter a máxima deformação residual.

ABSTRACT The wide knowledge of the thermomechanical behavior of shape memory alloys (SMAs) is necessary to obtain alloys with high thermal hysteresis, which makes it possible to eliminate the need for cryogenic means in many applications. In this way, the mathematical models appear as an effective alternative to describe this thermomechanical behavior. In the present work, a mathematical model was developed able to measure the residual strain for a Cu-Al-Be-Nb alloy as a function of the variables: strain, temperature and strain rate. It is observed that the results obtained through the model are presented with good agreement when compared with the experimental data. Furthermore, it was found that the model is capable of predicting the conditions necessary to obtain the maximum residual strain.

Copper-based polycrystalline shape memory alloys (SMAs) have limitations for many practical applications due to their low superelasticity and low ductility. In order to overcome this situation, in recent years, the production of copper-based SMAs by directional solidification process has attracted the interest of many researches. In this sense, the present work had as objective to evaluate, through instrumented indentation tests, the influence of the solidification direction on the elastic modulus, hardness and superelasticity of a Cu-Al-Be-Nb-Ni alloy produced by directional solidification. The results showed that the superelasticity, remnant depth, elastic modulus and hardness DHV-1 are strongly dependent on the direction of application of the load in relation to the solidification direction, that is, the alloy presented an anisotropic behavior for its mechanical properties.

The understanding of the stabilization mechanism of martensite used to obtain alloys with high hysteresis and the possibility of recovering this martensite (residual strain) by heating at temperatures higher than As and Af have been fundamental for application in bonding devices. One of the possibilities to enhance residual strain is through mechanical cycling. This work evaluated the influence of number of cycles and the effect of precipitation of Nb-rich particles as mechanisms to increase residual strain in superelastic Cu-Al-Be-Nb alloys. The results showed that the presence of Nb-rich precipitates was not a predominant factor for the enhancement of residual strain. In addition, mechanical cycling has proved to be an efficient mechanism for raising residual strain, and consequently increasing the amount of martensite retained. However, the gain of residual strain is accompanied by an increase of plastic deformation.