Estudo de uma liga Cu-Al-Ni com memória de forma visando aplicações em sistema de proteção contra sobrecargas elétricas.

Abstract

This work is dedicated to the study of a Cu-Al-Ni shape memory alloy (SMA) aiming applications for protection against electrical overloads. It was studied the nominal chemical composition Cu-13,5Al-4,0Ni (wt%). The raw materials used to obtain the Cu-Al-Ni ingots were massive bars of the commercially pure elements melted in an air induction furnace. Samples cutted directly from the obtained ingots were betatized at 900°C during 15 minutes followed by quenching in water at room temperature (~27°C). The sheet samples were characterized by electrical resistance as a function of temperature to determine the phase transformation at the origin of the shape memory phenomena. Others techniques like optical microscopy, micro hardness and force recovery as a function of temperature were employed to complement the characterization. The results obtained with the laboratory Cu-Al-Ni SMA were compared with the ones from a same alloy supplied by Societe Trefimetaux (France). The transformation temperatures (MS=128°C), micro hardness in the martensitic phase (HV 250) and average grain size (~600um) were similar for both alloys, however the laboratory alloy has demonstrated a minor intensity of force recovery (-125N) during heating. The studied alloy has a good potential for electrical applications because theoretical simulations have demonstrated that the Cu-Al-Ni SMA sheets can respond more rapidly to the electrical current than the classical protection systems available in the market.