Metastable solidification of NdFeB alloys by drop-tube processing

Abstract

Metastable solidification of small droplets of Nd11.8Fe82.3B5.9 and Nd14Fe79B7 alloys was performed in an 8-m drop tube filled with helium. The results showed that the solidification path of the droplets depends on the alloy composition and on the droplet size. For Nd11.8Fe82.3B5.9 alloy, larger droplets are solidified by primary iron formation and subsequent Nd2Fe14B crystallization from the residual liquid phase, whereas smaller ones tend to be frozen by metastable primary Nd2Fe17Bx growth (x = 0–1). A similar transition of the solidification path from primary iron formation to primary Nd2Fe17Bx formation occurred in Nd14Fe79B7 alloy with reducing droplet size. However, metastable primary growth of Nd2Fe14B was also observed within a wide droplet size range prior to the appearance of the metastable Nd2Fe17Bx phase. Nucleation and growth of different phases were considered to produce an explanation of the observed phase selection phenomena in these two alloys.