Study On Phase Equilibria Of RE-Mn-Si(RE=Nd,Gd) Alloys

The RE-Mn-based compounds show complex and various magnetic properties(e.g.magnetocaloric effect,magnetoresistance and spontaneous magnetostriction)due to their unique crystal structures.Phase equilibria of the RE-Mn-based systems are useful to study the crystal structures and magnetic properties of these intermetallic compounds.In this work,phase equilibria of the Nd/Gd-Mn-Si ternary systems were investigated experimentally by X-ray diffraction(XRD),scanning electron microscopy(SEM)with energy dispersive spectrometry(EDS).The following conclusions would be drawn:(1)The phase structure,phase composition and microstructure of four Nd-Si key alloys prepared by arc-melting were analyzed by by XRD and SEM/EDS.The stability and composition ranges of the intermetallic compounds in Nd-Si alloys were studied.The experimental results show that the intermallic compounds,Nd Si,Nd₂Si₃and Nd Si_x,are stable,while the intermallic compound Nd₃Si₄is not stable.The composition ranges of the intermetallic compounds Nd Si,Nd₂Si₃and Nd Si_xat 673 K,873 K and 1273 K were measured respectively.(2)Nd-Mn-Si ternary alloys with different compositions were prapared by arc melting technique.Nd-Mn-Si ternary alloys annealed at 673 K for 2400 hrs and at 873 K for 1440 hrs were examined by XRD and SEM/EDS.The ternary intermetallic compounds,Nd Mn Si,Nd Mn₂Si₂,and Nd Mn Si₂were confirmed to be stable at 673 K and 873 K.The isothermal sections of the Nd-Mn-Si ternary system were determined finally.(3)Gd-Mn-Si alloys were prapared by arc melting technique.The phase structure and microstructure of Gd-Mn-Si alloys annealed at 1073 K for 720 hrs were tested by XRD and SEM/EDS.Three stable ternary intermetallic compounds,Gd Mn Si,Gd Mn₂Si₂and Gd₂Mn₃Si₅,were confirmed.Phase equilibria of the Gd-Mn-Si ternary system at 1073K were obtained.