Effects Of Alloying And Shortly High Temperature Annealing On Microstructure And Magnetic Properties Of La-Fe-Si Alloys

La(Fe,Si)i3, possessing the structure similar with cubic NaZn13-type, is a potential material for room-temperature magnetic refrigeration, but the preparation technology is very difficult. A single-phase material is usually obtained by annealing as-cast bulk ingots at elevated temperatures for several weeks, thus calling for more highly efficient preparing techniques.Alloys of composition,(La1-zCez)Fe13-xSix, La(Fe13-x-mCom)Six, LaFe13-x(Si1-yAly)x by the way of substituting La, Fe and Si atoms by Ce, Co and Al atoms; LaFe13-xSix, LaFe12-xCoSix using for annealing, were prepared using the arc-melting technique and the induction melting technique. Then, the LaFe13-xSix and LaFe12-xCoSix alloys were annealed at high temperature for a short time. Phase constituents and microstructure of the alloys were investigated by x-ray diffraction (XRD) analysis and scanning electron microscopy (SEM), magnetic properties of some annealed samples were measured by physical property measurement system (PPMS). Major findings and conclusions were summarized as follows:1. The La(Fe,Si)13compound was not formed in induction-melted (La1-zCez)Fe13-xSix (z=0.1,0.2,0.5,1.0; x=1.0,1.5,2.0,2.5,3.0) alloys even Ce element was added. These phases such as a-(Fe,Si),(La,Ce)FeSi,(La,Ce)Fe2Si2, Ce2(Fe,Si)17, Fe3Si were crystallized from the liquid phase. The primary phase crystallized becomes the (La,Ce)Fe2Si2phase rather than the α-(Fe,Si) one with the content of Si increased.2. In the induction-melted La(Fe13-x-mCom)Six(m=1,2,5,13-x; x=1.0,1.5,2.0,2.5,3.0) alloys, if Fe element was completely replaced by Co element in the La-Fe-Si alloys, high content of La(Co,Si)13phase is generated, whereas the cubic structure La(Co,Si)13phase is formed, when the content of Si element was increased from1.0to2.0, and, when the content of Si element is2.5or3.0, tetragonal La(Co,Si)13phase was crystallized. 3. In the induction-melted LaFe13-x(Si1-yAly)x (y=0.1,0.2,0.5,1.0; x=1.0,1.5,2.0,2.5,3.0) alloys, phases such as a-(Fe,Si,Al), a-(Fe,Al), LaFeSi, LaFeAl, Fe3Si, Fe3(Si,Al) were crystallized from the liquid phase. All Al element present itself in the solution of a-(Fe,Si,Al). With the content of Si increased, the primary phase becomes the LaFe2Si2phase rather than the α-(Fe,Si,Al) one. A little La(Fe,Al)13phase with Cubic NaZn13-type was formed in LaFe10.0Al3.0compounds.4. In annealed LaFe13-xSix(x=1.0-1.5) alloys, the content of cubic La(Fe,Si)13phase increased when the annealing temperature increased with the same composition, while increases when the Si content rise in the same annealing temperature. When annealing temperature is higher, La-rich phase is easier to form.5. In annealed LaFe12-xCoSix(x=1.0-1.5) alloys, the content of cubic La(Fe,Co,Si)13phase increased when the annealing temperature increased with the same composition of low Si content alloys and La element is easier to appear at the edge of samples when annealing temperature is higher. The magnetic entropy of all alloys is small, the Curie temperature of LaFe12-xCoSix compounds decreased with the content of Si element increases after annealing at1200℃.