Optimizing the Caloric Properties of Cu-Doped Ni–Mn–Ga Alloys

Abstract

With the purpose to optimize the functional properties of Heusler alloys for their use in solid-state refrigeration, the characteristics of the martensitic and magnetic transitions undergone by Ni50Mn25−xGa25Cux (x = 3–11) alloys have been studied. The results reveal that, for a Cu content of x = 5.5–7.5, a magnetostructural transition between paramagnetic austenite and ferromagnetic martensite takes place. In such a case, magnetic field and stress act in the same sense, lowering the critical combined fields to induce the transformation; moreover, magnetocaloric and elastocaloric effects are both direct, suggesting the use of combined fields to improve the overall refrigeration capacity of the alloy. Within this range of compositions, the measured transformation entropy is increased owing to the magnetic contribution to entropy, showing a maximum at composition x = 6, in which the magnetization jump at the transformation is the largest of the set. At the same time, the temperature hysteresis of the transformation displays a minimum at x = 6, attributed to the optimal lattice compatibility between austenite and martensite. We show that, among this system, the optimal caloric performance is found for the x = 6 composition, which displays high isothermal entropy changes (−36 J·kg−1·K−1 under 5 T and −8.5 J·kg−1·K−1 under 50 MPa), suitable working temperature (300 K), and low thermal hysteresis (3 K).

Sequence and Characteristics of Atomic Ordering in Ni2Mn1−xCuxGa Ferromagnetic Shape Memory Alloys

“…Figure 10 shows the DSC curves obtained for alloys with different Cu content (3–11 at% Cu) quenched from 1020 K during the first (solid lines) and second (dashed lines) heating runs. In Figure 10 , along with the variation of the MT and Curie temperatures owing to Cu content [ 5 ], the exothermic peaks P L and P H are also observed to change.…”

“…Among doping elements, Cu has been extensively studied, since the sequence of magnetic/structural transformations can be tailored by changing the Cu content and the element it replaces. In summary, Cu substituting Mn or Ga increases the T MT and decreases both the austenite and martensite T C [ 4 , 5 ]; instead, Cu substituting Ni lowers T MT and raises T C [ 6 ].…”

Magnetic and Magnetostrictive Properties of Ni50Mn20Ga27Cu3 Rapidly Quenched Ribbons

“…Previous studies indicate that the partial Cu-doping of Ni-Mn-Ga as bulk [9][10][11] or ribbons [12,13] allows for the smooth adjustment of the magnetic and structural transition temperatures. The first principles calculations suggest that, if present in a small amount, the Cu atoms prefer taking the sublattice of the host element in deficiency [14].…”

Investigation of shape memory effect in Ni-Ti based alloys

“…Later, a series of other shape memory alloys (SMAs) were manufactured such as Cu-based alloys (Cu-Zn, Cu-Sn), Ni-based alloys (Ni-Ti, Ni-Al), Fe-based alloys (Fe-Pd, Fe-Pt) . However, the most commonly used SMAs are nitinol alloys (Ni-Ti) and Heusler alloys (Cu-Ni-Al, Ni-Mn-Ga) [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Recently, the SME has been observed on some high entropy alloys (HEAs) such as Ti-Ta-Hf-Nb-Zr, Fe-Ni-Co-Al-Ti, Ti-Zr-Co-Ni-Cu.…”

“…The SME in Cu-Al-Mn Heusler alloys was first published in 1996 [22]. The superelasticity (SE) of these alloys is improved through controlling structure and particle size [23][24][25][26][27][28][29][30][31]. So far, the superelastic property of these alloys has reached the level of Ni-Ti ones.…”