The Study On The Phase Diagram And Magnetocaloric Property Of The Gd-Co-Al Ternary System

The phase diagram of Gd-Co-Al ternary system,the structure and magnetocaloric property of the GdCo_2-xAl_x alloys were investigated by X-ray diffraction(XRD) ,differential thermal analysis (DTA), scanning electron microscopy (SEM) and magnetic measurement techniques in this paper.The results of the 900℃and 500℃isothermal section of Gd-Co-Al ternary system were presented.The 900℃isothermal section of Gd-Co-Al system (Gd≤33.3%) consists of 14 single-phase regions (δ(GdCo_0.74Al_1.26),α(Gd₂Co₇),β(Co),γ(Gd₂Co₁₇),θ(GdCo5),ε(GdCo₃),ζ(GdCo₂),η(GdAl2),ι(GdAl3),κ(Co₂Al9),λ(Co4Al13),μ(CoAl3),ν(Co₂Al5),ω(CoAl) ), 25 two-phase regions (β+γ,γ+θ,θ+α,α+ε,ε+ζ,θ+ε,θ+ζ,ζ+δ,η+δ,δ+ω,ω+ζ,ω+θ,ω+γ,ω+β,ω+η,ω+ι,ω+ν,ν+ι,ν+μ,μ+ι,μ+λ,λ+ι,λ+κ,κ+ι,ι+η) and 12 three-phase regions (δ+ω+ζ,δ+ω+η,β+ω+γ,ω+γ+θ,θ+ω+ζ,θ+α+ε,ζ+ε+θ,ω+ι+η,ω+ι+ν,ν+μ+ι,ι+μ+λ,λ+κ+ι).The 500℃isothermal section of Gd-Co-Al system consists of 22 single-phase regions, 43 two-phase regions and 22 three-phase regions. The 22 single-phase regions are:δ(GdCo_0.74Al_1.26),θ(Gd₂Co₂Al),α(Co),β(Gd₂Co₁₇),γ(GdCo₅),ε(Gd₂Co₇),χ(GdCo₃),η(GdCo₂),ι(Gd₄Co₃),κ(Gd₃Co),λ(Gd),μ(Gd₂Al),ν(Gd₃Al₂),ξ(GdAl),ο(GdAl₂),Ï€(GdAl₃),ρ(Al), (?)(Co₂Al₉),σ(Co₄Al₁₃),Ï„(CoAl₃),Ï…(Co₂Al₅),φ(CoAl). The 43 two-phase regions are:α+β,β+γ,γ+ε,ε+χ,χ+η,η+ι,ι+κ,κ+λ,λ+μ,μ+ν,ν+ξ,ξ+ο,ο+Ï€,Ï€+ρ,ρ+(?),(?) +σ,σ+Ï„,Ï„+Ï…,Ï…+φ,φ+β,φ+γ,φ+η,φ+δ,φ+ο,φ+Ï€,γ+η,γ+ε,η+θ,θ+δ,θ+ι,δ+η,δ+ο,δ+κ,θ+κ,Ï€+Ï…,Ï€+Ï„,Ï€+σ,Ï€+(?),ο+ι,ο+κ,κ+ξ,κ+ν,κ+μ. The 22 three-phase regions are:λ+κ+μ,μ+κ+ν,ν+κ+ξ,ξ+ο+κ,κ+ο+δ,ι+κ+θ,δ+κ+θ,θ+ι+η,η+θ+δ,η+χ+ε,ε+η+γ,α+β+φ,φ+β+γ,γ+φ+η,η+φ+δ,δ+φ+ο,ο+Ï€+φ,φ+Ï€+Ï…,Ï…+Ï„+Ï€,Ï€+Ï„+σ,σ+Ï€+(?),(?)+Ï€+ρ.The influence of Al addition to the microstructure, the magnetic properities and magnetocaloric effect of GdCo_2-xAl_x (x=0, 0.06,0.12, 0.18,0.24, 0.3, 0.4) alloys were investigated. The lattice constants of the alloys enlarge almost linearly with the Al addition, while they all are cubic type with the Cu₂Mg structure. Al substitution for Co at first increase the Curie temperature, and then decreases. The maximum value of the Curie temperature Tc=418 K, is achieved for GdCo1.94Al0.06. The magnetic entropy decreases with increase of the Al content. The maximum value of the magnetic entropy |ΔS_M| =2 .31J/kg·K, is achieved for GdCo₂ in an applied field of 1.5 T. It is sure that this result will benefit the work of finding new magnetic refrigeration materials and the research of magnetocaloric effect.