Diffusion of Fe, Co, Nd, and Dy in R-2(Fe1-xCox)(14)B where R = Nd or Dy

Transition metal and rare earth diffusion coefficients at 1323 K in Dy2-yNd y(Fe1-xCox)(14)B were determined by field emission energy dispersive spectr oscopy compositional analysis of diffusion couple specimens. Various arrang ements of component materials and temperatures were examined in order to un derstand the mechanisms affecting diffusion of the components and to predic t the stability of functionally graded microstructures consisting of a dysp rosium-rich (Dy2-yNdy(Fe1-xCox)(14)B) outer layer and a neodymium-rich (Nd- 2(Fe1-xCox)(14)B) interior. Estimates of the mutual interdiffusion coeffici ents of Dy, Nd, Fe, and Co in this system were obtained from the preparatio n of arc melted and annealed polycrystalline specimens, assuming that the d iffusion coefficients were independent of concentration (Grube solution). F ifteen diffusion couples were prepared and heat treated at 1323 K for vario us times in order to provide data for calculation of the diffusion coeffici ents. The results indicate that the diffusion coefficients of Fe and Co (D- Fe = 3.28 x 10(-10)cm(2)/s and D-Co = 7.63 x 10(-10)cm(2)/s) were significa ntly higher at 1323K in this system than those for Dy and Nd (D-Nd = 2.3 x 10(-12)cm(2)/s and D-Dy = 2.9 x 10(-12)cm(2)/s). (C) 2001 Elsevier Science B.V. All rights reserved.