The eutectoid decomposition reaction that occurred in RECo5 phases（RE=Dy and Gd ） at low temperature was discussed and confirmed by X-ray powder diffraction（XRD）, differential thermal analysis, and scanning electron microscopy.The decomposition temperature of the GdCo5 and DyCo5 were identified as 805.8 and 900 °C, respectively.The GdCo5 and DyCo5 phases could not be found in the isothermal section of Gd-Dy-Co ternary system at 800 K.Reasons for the absence of the RE2Co7 phase in the XRD patterns were discussed in detail.
