Reaction sintering and mechanical alloying

Microstructural examination of their samples quenched from different stages of the process shows that two different diffusion paths (labeled A and B in fig. 43) are followed. Each path leads separately to particles of the phase Nd2Fe14B ( j ). In order of increasing temperature the following events occur  

Boron diffusion leads to the formation of j according to the reaction scheme 

Schneider et al. (1986b) note that path A, involving the Fe particles, is faster than path B that consumes the Fe2B particles. Consequently, the j grains that have their origin in Fe particles have the possibility to grow more than the others and one can expect the grains to have a bimodal size distribution. 

The values of the coercive forces thus far attained by Stadelmaier et al. (1985) in this way are in excess of 500 kA/m, the maximum B value generally staying below 1 T. The authors report that the powder processing can be done entirely in air and that the results are reproducible. 

The author noted that Dy203 (or Tb407) additives as powder are preferred compared to metal substitution owing to the high price of metallic Tb or Dy. Similar results were also reported by Ho Wen Wang (1987b). 

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