不同成分DyM(M=Cu、Al)合金粉對燒結NdFeB永磁體晶界擴散及磁性強化效應之研究

Magnetic properties enhancement of sintered NdFeB magnets by using DyM (M=Cu、Al) alloy powders for grain boundary diffusion.

吳政勳(Cheng-Hsun Wu)

指導教授 ： 張文成

國立中正大學/理學院/物理學系/碩士(2015年)

摘要

本實驗探討以不同成分之低熔點DyCu、DyAl合金粉並改變擴散處理溫度及時間，以及透過調變製作粉體時之銅輪轉速(v)，探討合金粉結晶性及粒徑大小對5 mm 厚燒結NdFeB磁石晶界擴散效應及對其磁特性質影響進行研究。第一部分探討不同成分DyM (M=Cu、Al)合金粉(平均〜30 um大小)之效應。結果顯示在同一熱處理條件下，隨著合金熔點下降合金粉流動性增加，擴散效率提升，本質矯頑磁力也隨之提升。其中DyCu 粉之效應高於DyAl粉，而 Dy0.85Cu0.15粉最高可提升磁石iHc達7.4 kOe。第二部分探討低熔點Dy0.7Cu0.3合金粉之熱處理條件，以找尋低熔點合金粉的最佳擴散溫度及條件。結果顯示低溫(840 0C)擴散處理需為高溫(900 0C)的兩倍時間才能獲得相同效果。合金粉利用低溫擴散跟高溫擴散的路徑稍有不同，高溫擴散合金粉的流動性較佳，較多會直接進入晶界沿晶擴散進入磁體內部的晶界。而低溫擴散因合金粉體流動性較差，在磁石表面停留太久而易造成穿晶擴散進入磁體內部，再進行晶界擴散。第三部分探討Dy0.7Cu0.3合金粉的結晶性對NdFeB磁石晶界擴散效應及磁性之影響。透過調變銅輪轉速製作不同結晶度之合金薄帶，再予以粉碎後進行晶界擴散處理。轉速較快所製作之合金粉結晶性較差，擴散處理時需要先經過結晶過程後再進行晶界擴散，擴散效率較差，磁特性也受到影響。而本系列最好的磁特性出現在採用v=15m/s之合金粉，其iHc之提升量為7.1 kOe。第四部份以球磨製做超細粒徑(約6μm)之Dy0.7Cu0.3合金粉來做晶界擴散所用之擴散源，研究粒徑大小是否會影響磁特性之變化。結果顯示磁特性與粒徑大小有關，其Δ iHc約可達5.3 kOe，小於粗合金粉之7.1 kOe。
關鍵字:合金粉、釹鐵硼磁石、晶界擴散

關鍵字

釹鐵硼磁石 ； 合金粉 ； 晶界擴散

並列摘要

The effects of composition of low melting DyCu and DyAl powders, wheel speed, particle size after pulverization and diffusion condition on coercivity enhancement (∆iHc) and microstructure of grain boundary diffusion (GBD) treated NdFeB magnets (5 mm in thickness) were reported. At first, the effect of composition of DyM (M=Cu and Al) powders of about 30μm was investigated. The result showed that ∆iHc was enhanced with the decrease of melting point of the alloy powders due to the increased flow ability during diffusion. DyCu powders display superior effect to that of DyAl powders. The optimal ∆iHc of 7.4 kOe was obtained for the case of Dy0.85Cu0.15 powders. Secondly, the effect of heat treatment condition on low melting Dy0.7Cu0.3 was investigated. Low temperature (840 0C) diffusion treatment requires twice time than the high temperature (900 0C) diffusion to achieve identical effect. The powders with high temperature diffusion have better flow ability which makes them enter the interior of the magnets mainly through the grain boundaries. Nevertheless, most of the powders prefer to enter the magnets through the grains at the beginning followed with the grain boundary diffusion, if low temperature diffusion process was employed. Thirdly, the alloy powders with different crystallinity were prepared by melt spinning followed by pulverization. The powders made by higher wheel speed exhibit worse crystallinity which makes them have inferior diffusion efficiency to those powders with fully crystalline structure. The alloy powders made with v=15m/s lead to the highest ∆iHc of 7.1 kOe. Finally, fine Dy0.7Cu0.3 powders of 〜6μm were adopted for grain boundary diffusion. △ iHc of 5.3 kOe is obtained which is lower than the value of 7.1 kOe achieved for coarser alloy powders, yet it is higher than the effect using DyF3 as the diffusion source.
Key Word: NdFeB、DyM (M=Cu、Al)、Grain boundary diffusion

並列關鍵字

Grain boundary diffusion ； DyM (M=Cu、Al) ； NdFeB

參考文獻

[4] Nesbitt, E. A., Wernick, J. H. & Corenzwit, E. Magnetic Moments of Alloys and Compounds of Iron and Cobalt with Rare Earth Metal Additions. Journal of Applied Physics 30, 365-367 ( 1959).

[5] Hubbard, W. M., Adams, E. & Gilfrich, J. V. Magnetic Moments of Alloys of Gadolinium with Some of the Transition Elements. Journal of Applied Physics 31, S368-S369 ( 1960).

[6] Strnat, K., Hoffer, G., Ostertag, W. & Olson, J. C. Ferrimagnetism of the Rare‐Earth‐Cobalt Intermetallic Compounds R2Co17. Journal of Applied Physics 37, 1252-1253 (1966).

[7] Strnat, K. J. Cobalt, 133 (1967).

[8] Velge, W. A. J. J. & Buschow, K. H. J. Magnetic and Crystallographic Properties of Some Rare Earth Cobalt Compounds with CaZn5 Structure. Journal of Applied Physics 39, 1717-1720 (1968).