Microstructure evolution of peritectic Nd14Fe79B7 alloy during directional solidification

• Published in: Journal of crystal growth Vol. 310; no. 14; pp. 3366 - 3371
• Main Authors: Zhong, Hong, Li, Shuangming, Lü, Haiyan, Liu, Lin, Zou, Guangrong, Fu, Hengzhi
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier 01-07-2008
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; General studies of phase transitions; Growth from melts; zone melting and refining; Materials science; Methods of crystal growth; physics of crystal growth; Nucleation; 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; Nucleation; Directional solidification; Growth interface; Ternary alloys; 75.50.Bb; Rare earth compounds; Phase transitions; B1. Rare earth compounds; Dendrites; Bridgman method; Iron base alloys; Solidification front; A1. Directional solidification; A1. Nucleation; Neodymium alloys; Boron alloys; 81.30.Fb; A2. Bridgman technique; 64.60.-i; Solidification rate; A1. Morphological stability; A1. Peritectic; Growth mechanism; Microstructure; Crystal growth from melts
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2008.04.022

Bridgman type directional solidification experiments were carried out in Nd14Fe79B7 alloy. Microstructure evolutions along with growth velocities were investigated. At low velocities from 1 to 200 mum/s, the microstructures consisted of leading -Fe dendrites and peritectic Nd2Fe14B phase in the interdendritic region. At medium velocities of 425 and 500 mum/s, an incomplete banded structure formed, containing circles of -Fe/Nd2Fe14B-Nd2Fe14B dendrites. At high velocities of 1, 3 and 5 mm/s, a transition from gamma-Fe dendrites to Nd2Fe14B dendrites occurred. Phase selection phenomena were theoretically studied using the extremum criterion which assumes growth-controlled phase selection. The theoretical results are in agreement with experimental results at low velocities of 1-200 mum/s and high velocities of 3 and 5 mm/s. The incomplete dendritic bands at 425 and 500 mum/s were explained by nucleation of Nd2Fe14B phase at the gamma-Fe dendritic interface, and growth competition between gamma-Fe and the nucleated Nd2Fe14B phase. Phase transition from gamma-Fe to Nd2Fe14B at 1 mm/s was interpreted by abundant nucleation and quick growth of Nd2Fe14B phase at the gamma-Fe dendritic interface.