Structural studies of some hydrogen-treated materials related to the HDDR-process of Nd2Fe14B-based alloys

Hydrogen-treated Nd_14.0Fe_66.9Co_11.0 Ga_1.0Zr_0.1B_7.0 alloys have been examined by means of powder X-ray diffraction (XRD) and electron probe microanalysis (EPMA) to understand the mechanism of the development of magnetic anisotropy in the hydrogenation, decomposition, desorption, and recombination (HDDR) process of Nd₂Fe₁₄B-based alloys. It has been revealed that Nd₂Fe₁₄B phase can coexist in equilibrium with decomposed products, namely, α-Fe, NdH₂, and Fe₂B, in the presence of hydrogen of an atmospheric pressure over the temperature ranging 1113 to 1153 K. It was observed that Co and Ga condensed into a Nd₂Fe₁₄B phase during hydrogen-treatments, resulting in a thermodynamically stable Nd₂(Fe,Co,Ga)₁₄B compound. Well-developed anisotropic materials were obtained via the HDDR-process when the hydrogen-treatment was accomplished under such conditions that Nd₂ (Fe,Co,Ga)₁₄B coexists with the decomposed products. All our results give a favorable support to the previous proposal that the crystallographic orientation of the original alloy can be conveyed via the undecomposed Nd₂Fe₁₄B particles through-out HDDR processing