Alloy Preparation And Investigation On The Functional Behaviors For Directionally Solidified NiCoMnIn Alloys

Ni-Mn-In based alloys is a kind of multi-functional material discovered in recent years.It has many functions such as magnetocaloric effect and elastocaloric effect.NiMn-In series alloy has broad application prospects in refrigeration field,In this thesis,in order to improve the crystal orientation of the alloy and improve the functional behavior of the alloy,Ni45Co5Mn40-xIn10+x(x=0,1,2,2.5,3.3,3.4,3.5,4)alloys with strong orientation<001>A were prepared by directional solidification.Detailed characterizations were achieved by studying martensitic transformation temperature,crystal structure,microstructure,magnetic properties and mechanical properties,and the main results gained are as follows:Based on DSC analysis,with the increase of In content,the martensitic transformation temperature of the alloy decreased gradually.For every 1%increase in In atom,the phase transition temperature of the alloy is reduced about 40K.With the increase of In content,the phase transition temperature of alloy decreased gradually.XRD and SEM analysis showed that when In content≤13.3%,the alloy is a martensitic phase of a monoclinic structure with lath topography at room temperature.When the In content≥13.4%,the alloy is austenite with cubic structure at room temperature.The unit cell volume increases with the increase of In content.After directionally solidified,the original austenite of the alloy formed a coarse columnar crystal arranged along the direction of directionally solidified.Magnetic measurements show that the martensitic phase is weak magnetic martensite at room temperature when the In content≤13.3%.The austenite phase is ferromagnetic austenite at room temperature when the In content≥13.4%.Applying a magnetic field of 3 T significantly reduces the martensitic transformation temperature of the alloy.This shows that the magnetic field can induce reverse martensitic transformation.Under the 1.5 T magnetic field,the adiabatic temperature variation of Ni45Co5Mn36.7In13.3、Ni45Co5Mn36.6In13.4 and Ni45Co5Mn36.5In13.5 were 2.12 K,2.53 K and 1.68 K,respectively.Due to stress-induced martensitic transformation,the alloy have a significant elastocaloric effect in Ni45Co5Mn36.5In13.5.When the compressive strain is 5%and the loading rate is 3.5 mm/min,adiabatic temperature variation of the sample reaches the maximum value,which are 5.8 K and-5.6 K respectively during loading and unloading.In addition,no decay occurred after repeated 10 cycles.