Secondary dendrite arm coarsening and peritectic reaction in NdFeB alloys

• Published in: Journal of crystal growth Vol. 311; no. 2; pp. 420 - 424
• Main Authors: Zhong, Hong, Li, Shuangming, Liu, Lin, Lü, Haiyan, Zou, Guangrong, Fu, Hengzhi
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 2009; Elsevier
• Subjects: A1. Coarsening; A1. Dendrites; A1. Directional solidification; A1. Peritectic; A2. Bridgman technique; Alloys; B1. Rare earth compounds; Bridgman method; Coarsening; Cross-disciplinary physics: materials science; rheology; Crystal growth; Dendritic structure; Dissolution; Exact sciences and technology; Furnaces; Growth from melts; zone melting and refining; Materials science; Mathematical analysis; Methods of crystal growth; physics of crystal growth; Peritectic reactions; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Solidification; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation; A2. Bridgman technique; A1. Peritectic; A1. Coarsening; B1. Rare earth compounds; 75.50.Bb; A1. Directional solidification; A1. Dendrites; 81.30.Fb; Directional solidification; Temperature gradients; Iron; Rare earth compounds; Dissolution; Interfaces; Experimental result; Gamma phase; Growth mechanism; Dendrites; Bridgman method; Crystal growth from melts
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2008.11.047

Directional solidification experiments were performed on hyperperitectic Nd
13.5Fe
79.75B
6.75 alloy using a Bridgman type furnace. The relationship between secondary dendrite arm spacing (
λ
2) of primary γ-Fe phase as a function of growth velocity (
V) was established. Experimental results show that
λ
2 decreases with increasing
V and give a constant value
λ
2
V
0.33 of 5×10
−7
m
1.33
s
−0.33. Using arm coarsening theory, secondary arm spacing of γ-Fe dendrites was calculated, during which temperature gradient changing with growth velocity in the experiment was taken into account. The calculation gives a constant value
λ
2
V
0.31 of 8×10
−7
m
1.31
s
−0.31. Theoretical predictions are in reasonable agreement with experimental results. In peritectic reaction, the dissolution rate of γ-Fe dendrite arms varied from 0.0061 to 9.1
μm/s, as the growth velocity increased from 1 to 100
μm/s. The dissolution rate of γ-Fe dendrites was extremely small in low-velocity specimens with plane front peritectic interfaces.