Preparation of surface nanostructured sintered neodymium iron boron magnets by HDDR method

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The corrosion resistance and mechanical strength of sintered neodymium iron boron magnets have been improved through surface nanomaterialization.

A uniform oxide passivation film with nanostructures is formed on the surface to prevent further corrosion.

The smaller the grain size, the higher the mechanical strength, and the different crack shapes.

A prediction model for demagnetization curve of large volume magnets has been established, and the adverse effects on large volume magnets can be ignored.

abstract

A new method for protecting sintered neodymium iron boron magnets from corrosion by surface nanocrystallization (SNC) has been achieved using controllable hydrogenation dismutation desorption recombination (HDDR) technology. Compared to unprocessed magnets, SNC magnets have better corrosion resistance. The 50 μ m thick layer of dispersed Nd rich crystals on the nanocrystalline surface plays a crucial role in preventing intergranular corrosion. The corrosion test on SNC magnets showed that a highly oxidized and chemically uniform film was formed, preventing corrosion inside the magnet. The hardness test showed that after surface strengthening, a completely different crack morphology was observed. To verify its application capability, the effects of the reaction between bulk magnets and hydrogen at different depths on the tissue and magnetic properties were studied. For large magnets, this adverse effect can be almost negligible. This process has good corrosion resistance and surface strength, and can be used as a new method for surface treatment of large neodymium iron boron magnets.