Microstructure and Mechanical Behavior of Cu-Al-Ni-B Alloys with Thermoelastic Martensitic Transformation

Abstract

For the first time, using optical, scanning, and transmission electron microscopy and X-ray phase analysis in combination with measurements of tensile mechanical properties, we obtained data on the structural features of the polycrystalline shape-memory eutectoid Cu-Al-Ni-(B) alloys doped by aluminum (of 10 and 14 wt% Al in total amount), nickel (of 3, 4, and 4.5 wt% Ni), and boron (0.02–0.3 wt% B) in various compositions. The effect of boron on the grain sizes, structure, phase composition, and mechanical properties of shape memory (SM) alloys has been studied. The localization of aluminum borides in the structure was investigated and an effect of grain growth inhibition in the (α + β) and β Cu-Al-Ni-B alloys was established, both in the cast state of the alloys considered and after their heat treatment.

Effect of Controlled Heat Treatment and Aluminum Additions on the Strengthening of Cu–Ni-Based Alloys

“…This effect is attributed to a saturation of aluminum atoms in the Cu-Ni structure, where posteriorly aluminum segregation is promoted through the inter-dendritic regions [21], which is possibly due to a diffusion process. Hence, this mechanism occurs when aluminum atoms with lower atomic radii in comparison with Cu and Ni (0.5 Å) take preferential positions in the Cu-Ni lattice during the casting-solidification process; thus, by analyzing the images in Figure 1, the apparition of a second phase in samples with 10 at.% Al is observed, indicating that aluminum solubility in the Cu-Ni alloy is lower than the mentioned composition [22]. On the other hand, in the heat-treated samples, a significant amount of precipitates randomly distributed over the surface in comparison with untreated samples is observed [23].…”