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

Abstract

Cu-based superelastic shape memory alloys are promising for low-stress elastocaloric cooling. We have synthesized bulk alloys of 68Cu-16Al-16Zn under different conditions in order to promote its grain growth and enhance its elastocaloric properties. High-temperature X-ray diffraction of untreated 68Cu-16Al-16Zn alloy showed that the phase boundary between the α+β mixed phases and the high temperature phase (β phase) was between 973 K and 1023 K. Based on this result, the 68Cu-16Al-16Zn alloy was heated and cooled in a furnace repeatedly between 773 K and 1173 K. The maximum grain size after heat treatment of the ingot rolled to 67% reached 11.1 mm. The latent heat of the martensitic transformation after grain growth was 6.3 J g-1, which is higher than the previously reported value for the compound. The stress-strain curve of 68Cu-16Al-16Zn rolled to 67% rolling with cyclical heat treatments showed a maximum stress of 106 MPa at 4.5% strain, with adiabatic temperature change of 5.9 K in heating during stress loading and 5.6 K in cooling in stress removal. Furthermore, no fatigue in the stress-strain behavior was observed up to at least 60,000 mechanical cycles at 2% strain. These properties of the large grain 68Cu-16Al-16Zn alloys are very attractive for implementing them in elastocaloric cooling devices.

Large Cyclability of Elastocaloric Effect in Highly Porous Ni-Fe-Ga Foams

“…Elastocaloric refrigeration based on eCE is a promising cooling technology that can substitute conventional vapor compression, owing to its high compactness, environmental protection and energy-saving potential [ 2 , 3 ]. By utilizing the latent heat generated by the first-order martensitic transformation (MT), many SMAs such as Fe- [ 4 , 5 ], Cu- [ 6 , 7 ], TiNi- [ 8 , 9 ], MnNi- [ 10 , 11 ] and FeNi-based [ 12 , 13 ] systems can exhibit excellent eCE performance, which is characterized by large adiabatic temperature change (∆ T ad ) or isothermal entropy change (∆ S iso ) [ 14 ].…”