Preparation And Characterization Of Ni-Co-Mn-In/Al Magnetic Refrigeration Composites

Ni-Co-Mn-In alloy is a promising room-temperature magnetic refrigeration material due to its excellent magnetocaloric effects resulting from the magneto-structural transition.In order to improve the mechanical properties of the alloy,Fabrication of composite is effective way to improve the mechanical properties for Ni-Mn based bulk alloy.However,the study on Ni-Co-Mn-In composite is scarce.In the present work,Ni_45.2Co_5.1Mn_36.7In₁₃ alloy particles with a micron size were prepared by ball milling which were mixed with the pure Al powders followed by spark plasma sintering to obtain Ni_45.2Co_5.1Mn_36.7In₁₃/Al composites.The microstructure,martensitic transformation,magnetocaloric effects and mechanical properties of the Ni_45.2Co_5.1Mn_36.7In₁₃ particles and its composites were studied with scanning electron microscope（SEM）,X-ray diffractometer（XRD）,differential scanning calorimetry（DSC）,A.C.susceptibility and vibrating sample magnetometer（VSM）.It is found that,by using the high-speed vibration ball milling,Ni_45.2Co_5.1Mn_36.7In₁₃particles with an irregular shape were obtained.Their average size is smaller than 30μm and the size gradually decreases with the increase of ball to powder ratio and the milling duration.After ten minutes’or longer milling,the particles with or without post-annealing keep a L2₁structure and cannot exhibit the martensitic transformation.For those particles milled for less than ten minutes,after a proper annealing such as annealing at 800℃/1 h,the room temperature phase is 10M martensite.These particles undergo one-step martensitic transformation on heating/cooling.The transformation temperatures will get close to the bulk master alloy by adjusting the annealing conditions.The magnetic measurements results showed that,the particles subjected to 800℃/1 h-550℃/10 min annealing exhibit the best magnetic properties.Whereas,the magnetization difference between the martensite and austeniteΔM is still smaller,while the temperature range of martensitic reverse transformation being larger than that of the bulk master alloy,which leads to a smaller magnetic entropy changeΔS_M.At the magnetic field of 3 T,the maximumΔS_Mis 9.4 J/kg·K.To obtained Ni45.2Co5.1Mn36.7In13/Al composite,we firstly fabricated Ni45.2Co5.1Mn36.7In13particles with a size of 29.87μm by ball milling（ball to powder ratio is 4:1,milling time is 2min）.These particles were then mixed with pure Al powders and finally subjected to SPS.The obtained composites has a low compactness which exhibits a decreasing tendency with the weight fraction of Ni_45.2Co_5.1Mn_36.7In₁₃ particles.This greatly weakens the properties of the composites.SEM and XRD results confirmed there exist Ni-Co-Mn-In,Al and a little amount of unkown phases resulting from the diffusion and reaction along the interfaces.For Ni45.2Co5.1Mn36.7In13/Al composite,the martensitic transformation can be induced by both the temperature and magnetic fields.With increasing the weight fraction of Ni45.2Co5.1Mn36.7In13particles,M_s and A_f keep nearly constant,while Mf and A_sgradually shift,which leads to an increasingly widened transformation interval.The M-T curves show different characteristics in comparison with the bulk master alloy and particles.In addition,the values ofΔM is also remarkably lower than the bulk master alloy and particles.The above two reasons lead to a weak magnetetocaloric effects includingΔSM,RC andΔTad.For example,in S90 sample with the largest fraction of Ni_45.2Co_5.1Mn_36.7In₁₃ particles,the maximumΔS_M andΔT_ad is just 1.1J/kg·K and-0.12 K,respectively.The compressive experiment indicated that the compressive strength and fracture strain of NiCoMnIn/Al composites increase with decreasing NiCoMnIn content.But the mechanical properties of all the composites are worse than the bulk master alloy.The compressive strength of the composite containing 70 wt.%NiCoMnIn is 480.3 MPa and the fracture strain is 5.4%.