Corrosion resistance of (Nd,Dy)_(16)(Fe,Co)_(76-x)Ti_xB_8 mechanically alloyed magnets

摘要

Nanocrystalline (Nd,Dy)_(16)(Fe,Co)_(76-x)Ti_xB_8 magnets were prepared by mechanical alloying and respective heat treatment at 973-1073 K/30-60 min. An addition of 0.5 at. percent of Ti results in increase of coercivity from 796 to 1115 kA/m. Partial substitution of Nd by Dy results in an additional increase of coercivity up to 1234 kA/m. The highest corrosion resistance have magnets with 0.5-0.75-at. percent of Ti. Beside the Ti, the Co and Dy content significantly improve the corrosion resistance, too. It was found, that for Ti content smaller than x< 1, the (Nd,Dy)_(16)(Fe,Co)_(76-x)Ti_xB_8 powders are single phase. For higher Ti contents (x> 1) the mechanically alloyed powders heat treated at 973 K are no more single phase, and the coercivity as well as corrosion resistance decreases due to the presence of an amorphous phase and alpha-Fe. A heat treatment at a higher temperature (1073 K/30 min) or at 973 K for longer time (1 h) results in the full recrystallisation of the powders. The obtained homogenized structure results in higher corrosion resistance.