Microstructure and Thermal Analyses of Cu87-xAl13Nbx High-Temperature Shape Memory Alloys

Abstract

This paper presents a thermal and microstructural characterization of Cu 87-x Al 13 Nb x (wt%) high temperature shape memory alloys (HTSMA), with Nb contents ranging from 1 to 3%. The alloys were obtained by arc melting under argon atmosphere. Thermal characterization was performed by differential scanning calorimetry (DSC), revealing that the phase martensitic transformation of all the studied alloys occurs in the range of 200 ºC to 450 ºC. Thermal cycling in this temperature range caused the martensitic transformation to disappear after approximately 6 cycles. However, a new heat treatment at 850 ºC followed by water quenching causes the martensitic transformation to be recovered. Microstructural characterization was performed using optical microscopy (OM) and scanning electron microscopy (SEM), revealing the presence of Nb precipitates in a Cu-Al martensitic matrix, mainly in the Nb-rich compositions. These different microstructures with Nb particles cause a hardness variation that initially decreases between 0.5 %Nb (275HV) and 1.0 %Nb (225HV), then increasing continuously up to 3.0% Nb (380HV).

Study on Basic Characteristics of CuAlBe Shape Memory Alloy

“…As seen on these micro-images, the thin V-type and needle-like β1′(18R) martensites [5,8,9,23] that formed on the surface of the alloy can be seen clearly. The thick and collaterally formed γ1′(2H) martensites (e.g., in the darker grain region, seen on the top right-hand corner of the left image) and some dark spots of AlCu 3 (β1) precipitations [9,10,[23][24][25][26][27] are also visible in Fig. 4.…”