Study On Comprehensive Regulation For Magnetocaloric Effect And Mechanical Properties Of The?Mn,Fe?₂?P,Si? Alloys

Nowadays,refrigeration technology plays an important role in every aspect of our life.The traditional gas compression refrigeration is hard to meet the requirements of sustainable development,so a new refrigeration technology is urgently needed.Due to the advantages of high-efficiency and environmental-friendly,magnetic refrigeration technology has attracted widespread attention.The Curie temperatures of?Mn,Fe?₂?P,Si?alloys are near room temperature and continuously adjustable.What's more,the magnetic entropy changes and adiabatic temperature changes of?Mn,Fe?₂?P,Si?alloys are large,while the prices of raw materials are low.All these advantages ensure great potential in applications for?Mn,Fe?₂?P,Si?alloys.However,the?Mn,Fe?₂?P,Si?alloys are always hard and brittle.Moreover,the lattice paraments of?Mn,Fe?₂?P,Si?alloys often change abruptly during the phase transition,resulting in huge internal stress,which leads to cracks in the material and even overall fracture.The applications of?Mn,Fe?₂?P,Si?alloys in magnetic refrigeration are limited by these shortcomings.This article explores methods to improve the mechanical properties of Mn_1.05Fe_0.9P_0.5Si_0.5 alloy with its magnetocaloric effect maintained.Mn_1.05Fe_0.9P_0.5Si_0.5Cu_x alloys were prepared by arc-melting in this article.The results of XRD indicated that Cu doping did not affect the formation of the Fe₂P-type main phase in each sample.The magnetic entropy changes of Mn_1.05Fe_0.9P_0.5Si_0.5Cu_x alloys were considerable,which are 30.5,25.5,24.1 and 21.3 J?kg^-1?K^-1.Through long-term heat treatment,copper was precipitated on the grain boundaries of Fe₂P-phase,which could act as a buffer when the volume of the main phase grains changes,so the mechanical properties of Mn_1.05Fe_0.9P_0.5Si_0.5Cu_x alloys have been improved.However,due to a small amount of Cu atoms entering the lattice of Fe₂P-type main phase,the Curie temperatures of the Mn_1.05Fe_0.9P_0.5Si_0.5Cu_x alloys decrease from 321K to 290 K,264 K,and 248 K.The thermal hysteresis increases at the same time,which is disadvantageous for room-temperature magnetic refrigerations.In order to solve these problems caused by Cu doping,the method of Cu-B co-doping was applied.As the B content increases,the Curie temperatures of Mn_1.05Fe_0.9P_0.5-xSi_0.5Cu_0.10B_xalloys rise,and the thermal hysteresis decrease greatly from 51 K to 12 K.However,the excessive addition of B suppressed the segregation of Cu on the grain boundaries,so the improvement of mechanical properties by Cu-doping was weakened.In this article,the effects of Cu-B co-doping on microstructure,magnetocaloric effect and mechanical properties of?Mn,Fe?₂?P,Si?alloys were investigated,and the composition ratio with ideal comprehensive properties was proposed.Researches showed that for Cu-doped and Cu-B co-doped alloys,the direct smelting process made a small amount of Cu atoms enter the grains of Fe₂P-type phase.In order to avoid this defect,Mn_1.05Fe_0.9P_0.5Si_0.5 alloy was prepared first,then it was made into magnetic refrigeration composite material with tin-bismuth alloy as binder phase by low temperature hot pressing.Results showed the Curie temperatures of the Mn_1.05Fe_0.9P_0.5Si_0.5-Sn₄₂Bi₅₈ composite material is stable at about 305 K,while the mechanical properties improved.The thermal hysteresis of the composite material is reduced by 50%.In addition,the effects of composition ratios and hot-pressing pressures on the properties of Mn_1.05Fe_0.9P_0.5Si_0.5-Sn₄₂Bi₅₈ magnetic refrigeration composites were studied,and the optimized process parameters were proposed.In summary,this article focused on the shortage in mechanical properties of?Mn,Fe?₂?P,Si?alloys.The methods of elements doping?Cu doping,Cu-B co-doping?and preparing composite materials by hot pressing was adopted.The mechanical properties of Mn_1.05Fe_0.9P_0.5Si_0.5 alloy were improved,with its magnetocaloric effect maintained.This study provided new ideas for the comprehensive regulation for the magnetocaloric effect and mechanical properties of magnetic refrigeration materials,which promoted the application of magnetic refrigeration technology.