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Control of crystallite size in melt spun neodymium(2) iron(14) boron magnet material

Posted on:1995-04-08Degree:Ph.DType:Dissertation
University:Wayne State UniversityCandidate:Im, Jun SuFull Text:PDF
GTID:1471390014990579Subject:Engineering
Abstract/Summary:
The optimum composition for high performance {dollar}rm Ndsb2Fesb{lcub}14{rcub}B{dollar} permanent magnet material (HIREM) has been determined as {dollar}rm Ndsb{lcub}11.4pm 0.4{rcub}Fesb{lcub}82.14pm0.4{rcub}Bsb{lcub}5.44pm 0.4{rcub}{dollar} atomic percent. Using this material the melt spinning process has been studied by changing melt spinning chamber pressure and wheel speed to quantify their interdependencies as they relate to the control of microstructure and yield of HIREM. The experimental results show a significant influence of chamber pressure upon the melt spinning process. The influence of chamber pressure on the thickness of melt spun ribbons led to development of a new empirical relationship for ribbon thickness vs melt flow rate, wheel speed and chamber pressure. X-ray microstructure and magnetic property analysis on magnetically sorted powder material shows a gradual increase of energy product, up to 16.8 MGOe, as average grain size decreases to 200A. The energy product then sharply drops to a minimum value of 2 MGOe as the average grain size further decreases. It confirmed the average grain size for optimum HIREM material as 225 {dollar}pm{dollar} 25A. The best casts (at a 30 m/sec wheel speed with 400mmHg melt spinning chamber pressure) have a narrow average grain size range (206 {dollar}pm{dollar} 2A) and is closest to the optimum HIREM grain size range. The average measured energy product obtained from these casts is 16.78 {dollar}pm{dollar} 0.07 MGOe, with an average 9.9 kOe coercivity, 9 kG remanence, and with a 55.8 {dollar}pm{dollar} 0.54% average yield. Comparison of the estimated solidification thickness and cooling rate from a mathematical model with experimentally obtained ribbon thickness, average grain sizes and energy products indicate that our experimental results fit well on to the mathematical model used for the melt spinning process, except for the casts at 100 mmHg chamber pressure.
Keywords/Search Tags:Melt, Chamber pressure, Material, Size, HIREM
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