Microstructure, transformation temperatures, hardness and magnetic properties of Co36.4+Ni33.3−Ga30.3 ferromagnetic SMA

On the Impact of Additive Manufacturing Processes on the Microstructure and Magnetic Properties of Co–Ni–Ga Shape Memory Heusler Alloys

“…In literature, it is reported that the FOMST temperatures increase with increasing e/a ratio. [30,32,34,[36][37][38] As the Ga evaporation during DED processing causes an increase in the Co content and, thus, an increase in the e/a ratio, [49,53] the DED sample exhibits an increase in the FOMST compared with the as-cast material. The FOMST temperatures of the single-crystalline material do not depend on the direction in case of a low applied magnetic field of 0.05 T, considering the error bar of AE2 K (covered by the size of the symbol).…”

“…T t increases with increasing valence‐electron‐to‐atom ratio (e/a). The e/a ratio can be increased by substitution of Ga by Ni or Co by Ni or Ga by Co. [ 30,32,34,36–38 ] T t and M sat are also affected by the formation of secondary phases (γ and γ’‐phase), as their formation changes the chemical composition in the surrounding matrix (β‐phase). [ 17,27,39–41 ] The formation of γ’‐phase is observed after annealing between 623 and 873 K, [ 39,42,43 ] while the formation of γ‐phase is observed after annealing at higher temperatures between 973 and 1473 K. [ 27,40,44 ]…”

“…T t increases with increasing valence-electron-toatom ratio (e/a). The e/a ratio can be increased by substitution of Ga by Ni or Co by Ni or Ga by Co. [30,32,34,[36][37][38] T t and M sat are also affected by the formation of secondary phases (γ and γ'-phase), as their formation changes the chemical composition in the surrounding matrix (β-phase). [17,27,[39][40][41] The formation of γ'-phase is observed after annealing between 623 and 873 K, [39,42,43] while the formation of γ-phase is observed after annealing at higher temperatures between 973 and 1473 K. [27,40,44] In the present work, microstructure and magnetic properties of Co-Ni-Ga alloys processed by L-PBF and DED are compared with single-crystalline and polycrystalline cast material to determine the influence of the processing method and microstructure on the FOMST.…”

The Effect of the In-Situ Heat Treatment on the Martensitic Transformation and Specific Properties of the Fe-Mn-Si-Cr Shape Memory Alloys Processed by HSHPT Severe Plastic Deformation

“…NiTi alloys, Cu-based and Fe-based alloys are the most well known types of SMAs. Based on their crystalline structure in the austenitic phase they are grouped in “β-type” with body centered cubic (bcc) cell structure, a subclass of them being Ni-Ti [ 1 ], Co-Ni-Ga [ 2 , 3 , 4 ], Cu-Zn-Al, Cu-Al-Ni [ 5 ] and Ni-Mn-Ga [ 6 , 7 , 8 ], Ni-Fe-Ga Heusler alloys [ 8 , 9 ] and “γ-type”, with face centered cubic (fcc) cell structure, comprising Fe-Mn and Fe-Mn-Si [ 10 , 11 ], FePd [ 12 ] or FeNiCoTi [ 13 ]. Among these, Fe-Mn shape memory alloys present a good workability, weldability, corrosion resistance [ 14 ], large damping effect [ 15 ], recovery strain due to the shape memory effect (SME) [ 16 ] and superelasticity [ 17 , 18 ].…”

Phase formation and magnetic properties of nanocrytalline Ni70Co30 alloy prepared by mechanical alloying

“…Ni50Co50 In the case of polycrystals, in order to improve the properties of Co-Ni alloys, other elements are added to the binary alloys such as Fe, Ga, and Cu. For example, the Co-Ni-Ga alloy has been investigated; the study was devoted to the magnetic properties of Co36.4+ xNi33.3 -xGa30.3 system obtained by melting under controlled Argon atmosphere [16]. The magnetic hysteresis cycles obtained for four compositions (0  x  3.1 at.%) exhibited very narrow hysteresis loops.…”