Effect of Co-Doping on the Microstructure, Martensitic Transformation Behavior, and Magnetocaloric Effect of Ni-Mn-Sb-Si
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two decades, ferromagnetic shape memory alloys (FSMAs) have attracted much attention due to their multifunctional properties,[1,2] among which the Heusler-type Ni0.5Mn0.5xZx (Z = Ga, In, Sn, Sb) alloys exhibit shape memory effect (SME), superelasticity, magnetic-field-induced strain (MFIS), magnetoresistance (MR), magnetocaloric effect (MCE), elastocaloric effect (ECE), and exchange bias behavior[1,3–6] when the x = 0.23 to 0.25 for Z = Ga[7,8] and x = 0.13 to 0.15 for Z = In, Sn, Sb.[9–11] Unlike conventional MCE related to the first-order martensitic transformation (MT), Ni-Mn-Z (Z = In, Sn, Sb) alloys show inverse MCE during the magneto-structural transition process from paramagnetic/antiferromagnetic martensite phase to ferromagnetic austenite phase.[12–15] The great variation of magnetization between the martensite and austenite phase (DM) during the firstorder MT makes great contributions to the giant MCE
RUOCHEN ZHANG, XUEXI ZHANG, MINGFANG QIAN, and LIN GENG are with the School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China. Contact e-mail: [email protected] Mansucript submitted April 28, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
and MR in these Ni-Mn-Z (Z = In, Sn, Sb) alloys.[9,16,17] Recent studies revealed that Ni-Mn-Sb alloys exhibited anomalous magnetic properties related to the magneto-structural transition.[18,19] Khan et al[20] reported that Ni50Mn37+xSb13x alloys exhibited magnetic entropy change (DSM) of 17.7 J/kg K for x = 0, 14.7 J/kg K for x = 0.5 and 19.1 J/kg K for x = 1 under a magnetic field of 50 kOe, respectively. However, Ni-Mn-Sb alloys usually exhibit large magnetic hysteresis loss and narrow MT temperature range, resulting in small magnetic refrigeration capacity (RC) that limits their practical application.[18–20] Our previous work showed that partial substitution of Si for Sb in a quaternary Ni49.0Mn38.4Sb11.7Si0.9 alloy enlarged the MT temperature range and reduced the magnetic hysteresis loss, which accordingly improved the MCE around room temperature (RT).[21] Afterwards, we further systematically investigated the influence of Si-doping on the microstructure and phase transition behavior of Ni50Mn38Sb12xSix (x = 1, 2, 3) alloys. The results showed that when x = 3, secondary phases showed up and the Curie point of the austenite phase (TA C ) was lower than the MT temperature (TM) and both martensite and austenite phases exhibited a paramagnetic state during the structural transformation, resulting in an extremely low DM. Namely, DM is decreased
A as TA C gets lower, especially when TC is lower than [22] TM. In the present work, the substitution of Co for Ni is adopted to increase the TA C and DM because Co-doping can increase the magnetization of austenite phase, which has been demonstrated in Ni-Co-Mn-Z (Z = Ga, Al, Sn, and In) alloys.[23–26] For example, Nayak et al[2] reported that, compared with the un-doped Ni50Mn38Sb12 alloy, the TA C of Ni44Co6Mn38Sb12 alloy increased from 330 K to 350 K, and the TM decreased from 320 K to
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