R-T-B BASED ALLOY POWDER, COMPOUND FOR ANISOTROPIC BONDED MAGNET AND ANISOTROPIC BONDED MAGNET

摘要

The present invention provides R-T-B based alloy powders, wherein R represents at least one rare earth element, and T represents at least one element selected from the group consisting of ferrum and cobalt. The R-T-B based alloy powders have main phase grains, grain boundary phases and additive phases. The main phase grains are composed of R₂T₁₄B and have an average grain size of 200 nm or more and 500 nm or less. The grain boundary phases are richer in R than the main phase grains. With respect to any cross section of the R-T-B based alloy powders, the coverage of the main phase grains defined by equation 1 with the grain boundary phases with a roundness defined by equation 2 being 0.1 or more and 0.6 or less, is 10% or more and 40% or less.; $$ \begin{array}{cc}\mathrm{coverage}\equiv \frac{\sum _i^{}l_i}{\sum _j^{}L_j}l_i\text{:}\begin{array}{c}\mathrm{Circumference}\mathrm{of}\mathrm{each}\mathrm{grain}\\ \mathrm{boundary}\mathrm{phase}\end{array}L_j\text{:}\begin{array}{c}\mathrm{Circumference}\mathrm{of}\mathrm{each}\mathrm{main}\\ \mathrm{phase}\mathrm{grain}\end{array}& 〈\mathrm{equation}1〉\\ \mathrm{Roundness}=\sqrt{4\pi A\text{/}L^2}& 〈\mathrm{equation}2〉\end{array}$$ ;A represents the area of the cross section of the grain boundary phase, and L represents the circumference of the cross section of the grain boundary phase.