探討以低熔點合金DyM (M=Cu, Al)膜進行晶界擴散對燒結NdFeB磁石之磁特性影響

The Effect of Low Melting Point DyM (M=Cu, Al) Alloys on Magnetic Properties of Sintered NdFeB Magnets by Grain Boundary Diffusion Process

黃辰軒(Chen-Hsuan Huang)

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

本文探討Dy膜、DyCu合金膜、DyAl合金膜、Dy/Cu雙層膜及Dy/Al雙層膜濺鍍層對不同溫度下(800-950 ℃)進行晶界擴散的燒結NdFeB磁石之磁特性與微觀組織的影響。第一部分探討不同來源的Dy進行晶界擴散的效應。結果顯示不管是濺鍍金屬Dy膜或塗佈DyF3層皆可以提升本質矯頑磁力(iHc)，且進入磁體之Dy最大添加量皆為0.5-0.6 wt%Dy，其可使晶界擴散後的磁石之iHc提高6 kOe。第二部分探討不同稀土元素做晶界擴散的效用。結果顯示Tb提升磁體的本質矯頑磁力的能力比Dy來的高，但若考慮稀土元素的成本及所提升本質矯頑磁力的能力，Dy有較高的的性價比。第三部分則探討低熔點合金對於晶界擴散的影響。對於Dy膜、Dy85.6Cu14.4膜及Dy94.5Al5.5膜而言，其每1 wt%Dy所能提高的iHc (ΔiHc/wt%Dy)值，隨著熱處理溫度從800 ℃上升到850 ℃而隨之上升。然而在850-900 ℃時並無再向上提升之效果。與之不同的是，對於Dy/Cu雙層膜而言，其(ΔiHc/wt%Dy)值從Td為800 ℃上升到900 ℃的提升量幾乎是線性提升。又Dy85.6Cu14.4合金膜擁有最佳的ΔiHc/wt%Dy值，可達12.5 kOe/wt%Dy。其原因可歸於Dy85.6Cu14.4膜擁有較低的熔點，使其可以在低溫的擴散條件下擴散至磁體更深處。然而對Dy/Cu雙層膜而言，在800-850 ℃之間ΔiHc/wt%Dy值較低，卻在900 ℃時回復到12.8 kOe/wt%Dy，顯示在初始擴散時，Cu底層造成了Dy擴散的阻礙，當在900 ℃下擴散時，便有足夠的能量使Dy、Cu合金化並擴散至磁體深處。在本研究中可以明顯地觀察到，利用Cu來降低DyCu合金熔點可以有效的提高Dy在NdFeB磁石晶界擴散的效益，使ΔiHc/wt%Dy值可達12.5 kOe/wt%Dy，而僅需要0.4 wt%的Dy用量。

關鍵字

低熔點合金 ； 晶界擴散 ； 燒結釹鐵硼磁體 ； 直流濺鍍

並列摘要

The microstructure and magnetic properties of grain boundary diffusion (GBD) treated sintered NdFeB magnets at various diffusion temperatures (Td), using sputtered Dy, DyCu alloy, DyAl alloy, Dy/Cu bilayer films and Dy/Al bilayer films as the diffusion sources, were studied. At first, it was found that the coercivity of the magnets is effectively enhanced by using all the selected materials. The Dy content needed, for which the maximum coercivity enhancement (ΔiHc) of about 6 kOe is obtained, is 0.5-0.6 wt% by GBD with either Dy fluoride powders or Dy metal film. Secondly, the increment of iHc of the GBD magnets by Tb is higher than Dy. But from the view point of cost-performance ratio, Dy is better than that of the Tb. Finally, for various diffusion sources, ie., Dy, Dy85.6Cu14.4, Dy94.5Al5.5 films, the increment of iHc per wt% Dy (ΔiHc/wt%Dy) of the GBD magnets is increased with increasing Td from 800 oC to 850 oC, and then keeps constant with further increasing Td to 900 oC. Differently, ΔiHc/wt%Dy of the magnet with Dy/Cu bilayer is almost linearly increased with increasing Td up to 900 oC. At lower Td of 800-850 oC, the magnet with Dy85Cu15 alloy film exhibits higher ΔiHc/wt%Dy than that with Dy film due to the higher efficiency of Dy diffusion into the magnet, originated from the lower melting point of Dy85Cu15 than that of Dy. However, a slightly lower ΔiHc/wt%Dy was obtained for the sample with Dy/Cu bilayer at Td of 800-850 oC, reflecting an inferior Dy diffusion into the magnet might has occurred. Nevertheless, the magnets with Dy/Cu or Dy85Cu15 top layers both exhibited high value of ΔiHc/wt%Dy up to 12.4 kOe/wt%Dy at different Td. The above results reflect that adopting proper DyCu alloy film, or DyCu powders, for GBD treatment is a cost effective way in enhancing the coercivity of sintered NdFeB magnets.

並列關鍵字

low melting point alloys ； Grain Boundary Diffusion ； NdFeB

參考文獻

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