Effects of PM Processing Parameters and Alloying Elements on the Magnetic Properties of Sintered Iron Powders

乾壓成形與金屬射出成形之純鐵與鐵基合金軟磁零件，已廣泛地應於各項電子產品中，隨著電子產品的小型化，更凸顯粉末冶金製程在製造小型且形狀複雜之零件時，產量較高且成本較低的優勢，但由於製造過程中有添加高分子黏結劑，因此產品的雜質含量需要特別控制以獲得良好的磁性質。本實驗選用四種羰基鐵粉，測量在不同升溫速率、燒結溫度及燒結氣氛的情況下，純鐵燒結後之磁性質表現；本實驗也在純鐵粉中添加數種常用之合金元素，並使用工業界常用之燒結製程參數，以探討製造軟磁零件之可行性。 實驗結果發現，熱脫脂時之升溫速率對羰基鐵粉燒結後的磁性質有很大的影響，以不含SiO2之羰基鐵粉為例，熱脫脂過程中以3 ℃/min速率升溫之乾壓成形試片，於1350℃裂解氨氣氛下燒結一小時後，其磁性質與以5 ℃/min速率升溫之試片相比時，矯頑磁力減少13%且最大導磁率增加45%，分別達到141 A/m與3880。實驗結果也發現，在純鐵中添加合金元素後，對於熱脫脂過程之升溫速率可能變得更加敏感，以Fe-3 wt% Si為例，熱脫脂過程中以3 ℃/min速率升溫之乾壓成形試片，於1350℃裂解氨氣氛下燒結一小時及在真空中燒結兩小時後，其磁性質均不理想，但降低升溫速率至2 ℃/min時，試片之飽和磁束密度提升15%，矯頑磁力減少60%，最大導磁率增加60~70%。 本實驗結果顯示，不含SiO2且粒徑較小(D50=4μm)之羰基鐵粉，以乾壓成形，並以3 ℃/min之升溫速率於裂解氨氣氛中進行熱脫脂，再於1350℃裂解氨氣氛中燒結一小時，其密度達到7.45 g/cm3，以最大外加磁場1990 A/m測量時，飽和磁束密度為1.51 Tesla，殘留磁束密度為1.29 Tesla，矯頑磁力為141 A/m，最大導磁率為3880，為本實驗磁性質最佳之純鐵材料。本實驗也比較了含有2 wt%、8 wt%及50 wt% Ni之鐵鎳合金，以及Fe-49Co-2V合金的磁性質，其中Fe-50 wt% Ni之導磁率最佳為13467，而Fe-49Co-2V之飽和磁束密度最佳為1.86 Tesla。Iron and iron-base alloys made by Press and Sinter (P/S) process and Metal Injection Molding (MIM) process, are now widely used in a variety of electronic applications. The advantages of P/S and MIM parts include high yield and low cost. However, due to the polymeric binder added to the green parts, impurity level could be too high to achieve good magnetic properties. Four kinds of carbonyl iron powders are used in this study. The magnetic properties are measured after sintering in different heating rates, sintering temperatures and sintering atmospheres. Iron-base soft magnetic alloys are also examined in this study. The alloys are sintered using industrial production parameters to demonstrate its practicability. The results showed that magnetic properties are greatly influenced by the heating rate during thermal debinding. For the carbonyl iron powder without containing SiO2, when compacted and then sintered at 1350℃ in cracked ammonia for one hour, the coercivity decreased by 13% and permeability increased by 45% after decreasing the heating rate from 5 ℃/min to 3 ℃/min during thermal debinding, and reached 141 A/m and 3880, respectively. Similar behavior is shown in Fe-3 wt% Si alloys, when P/S Fe-3 wt% Si parts are sintered at 1350℃ in cracked ammonia for one hour and at 1350℃ under vacuum for two hours, the maximum induction increased by 15%, the coercivity decreased by 60%, and the permeability increased by 60~70%, when the heating rate is decreased from 3 ℃/min to 2 ℃/min. The best magnetic properties of P/S iron was obtained using OM powder and using a heating rate of 3 ℃/min for thermal debinding and sintering at 1350℃ in cracked ammonia for one hour. The properties were Bs=1.51 Tesla, Br=1.29 Tesla, Hc=141 A/m, and μmax=3880