Grain size evolution in Cu-based shape memory alloys

Abstract

A study of the grain growth kinetics in two shape memory alloys, CuAlBe and CuZnAl, is reported. Isothermal aging treatments at temperatures between 1023 and 1123 K were conducted, determining the grain size distribution as a function of time. The results show that the size distribution can be described by a log-normal type relationship, and is time-invariant. It was found that the arithmetic mean grain size almost coincide with the mode, which means that it is a representative parameter of the microstructure along the annealing time. The growth kinetics is strongly dependent on the aging temperature in CuZnAl, while is weakly in CuAlBe. It was verified that the grain size-time power law usually applied is not appropriate to describe the process, and an early departure from the ideal behavior is observed. The modification with a time-dependent dragging force gives a reasonable approximation to the grain growth kinetic. The obtained results are compared with the scarce data existing on this type of alloys.

Evaluation of Nb-Ni Influence on the Mechanical Behavior in a Cu-Al-Be Shape Memory Alloy

“…respectively in the maximum strain (6%). The grain refiners seem to have a reducing effect on the ductility of Alloy, as well show in other studies [26,34], so the strength increases considerably to submit the material to the same elongation, this is in accordance with the stiffness values shown previously.…”

“…As the grain size decreases the stress corresponding to the end of the initial linear part will referred as the martensite-start stress (σ ms ) increases, following a Hall-Petch relation type in β Cu-Al-Be [36,37]. This behavior has been found in other shape memory alloys [26,34,37]. To compare the results between the alloys produced, the σ ms were 44.1MPa, 53.4 MPa and 103.4MPa for Alloy 1 .…”

“…Alloy 2 and Alloy 3 , respectively. These results indicate that the effect of grain size on σ ms for Cu-Al-Be is stronger than for the other alloys [34].…”

“…respectively. It is worth mentioning that grain refinement of Nb in Cu-Al-Be SMAs have also been reported acts such as strengthening mechanism [33,34]. The grain size refinement is influenced of fine Nb-rich precipitates that form nucleation sites during the solidification.…”

Abnormal grain growth of 68Cu–16Al–16Zn alloys for elastocaloric cooling via cyclical heat treatments

“…One of the major issues in Cu-based SMAs is their cyclical fatigue property. The reason for the short fatigue life of Cu-based alloys is that their crystal grains are coarser than those of Ti-Ni owing to the tendency of thermal grain growth, which leads to grain boundary fracture when stress is applied [8][9][10][19][20][21]. Although attempts have been made to improve the crystal refinement and strength by adding Ti and V [21][22][23], there are drawbacks, such as smaller shape recovery properties [8].…”