Effect of Grain Size and Die-Upset Temperature on Texture in Die-Upset Nd-Fe-B Magnet

Hot-pressed Nd_13.5Fe₇₇Si₁B₈ alloy compacts with various grain sizes ranging from approximately 50 nm to 200 nm were prepared using melt-spun material. The compacts were then subjected to die-upsetting. The effect of grain size in the hot-pressed compact on the texture in die-upset magnet was investigated. The effect of die-upset temperature on the texture in die-upset magnet was also investigated. Texture in the die-upset Nd_13.5Fe₇₇Si₁B₈ alloy samples decreased with increasing the grain size in the hot-pressed compact before the die-upsetting. This dependence of texture on the initial grain size could be explained by the unique texture formation mechanism of a stress-induced preferential grain growth via dissolution and precipitation. Texture of the die-upset sample was also influenced by the die-upsetting temperature. The samples die-upset at 700degC and 900degC had poorer texture compared to the samples die-upset at the temperature range of 750degC-850degC. The poor texture in the sample die-upset at lower temperature of 700degC was attributed to the less dissolution of the unfavorable Nd₂Fe₁₄B grains and low fluidity of the liquid Nd-rich grain boundary phase. The poor texture in the sample die-upset at higher temperature of 900degC was explained by the reduced elastic modulus and the excessive grain growth of the Nd₂Fe₁₄B grains.