Enhanced Magnetic Properties of Nd 15 Fe 77 B 8 Alloy Powders Produced by Melt-Spinning Technique
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B magnets have been exploited in several industries including automotive, aerospace, electronics, telecommunication, power plants, etc., owing to their superior features since their discovery. As a recent trend, traditional motors have been replaced with the permanent magnet motors since permanent magnet motors have higher efficiency and consume lower energy.[1,2] Those magnets have excellent magnetic properties due to their tetragonal Nd2Fe14B compound, as it has an anisotropy field of 5.6 MA m1 approximately and a saturation magnetization of 1.6 T.[3] NdFeB magnets attracted many scientists and engineers due to their high coercivity.[1,4–6] The magnetic properties of the Nd-Fe-B magnets are significantly influenced by its microstructure and by the size
_ IN, _ SULTAN O¨ZTU¨RK, KU¨RS¸ AT IC and BU¨LENT O¨ZTU¨RK are with the Department of Metallurgical and Materials Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey. UG˘UR TOPAL is with the TUBITAK-UME, National Metrology Institute, 41470, Gebze-Kocaeli, Turkey. HU¨LYA KAFTELEN ODABAS¸ I is with the Department of Airframe and Powerplant, School of Aviation, _ GO¨BU¨LU¨K is with Firat University, 23180, Elazig, Turkey. METIN the Metin Otomotiv Sanayi 34953, Tuzla, Istanbul, Turkey. O¨MER NECATI_ CORA is with the Department of Mechanical Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey. Contact e-mail: [email protected] Manuscript submitted February 2, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
of the Nd2Fe14B crystallites and of the other coexisting phases.[7] As explained in previous classical studies, the microstructure of magnets may also affect demagnetization characteristics and domain structures.[8–10] It was reported that the individual Nd2Fe14B grains in melt-spin magnets are comparable to single magnetic domain with a 0.3 lm dimension. This dimension is considered critical in terms of hard magnetic properties.[9] This results in a high concentration of grain boundaries to elevate the resistance to domain movement when compared to coarser-grained magnets.[8,11] On the other hand, a-iron is soft phase and it badly affects the hard magnetic properties of Nd-Fe-B magnets.[12,13] It is, therefore, vitally important to understand crystallization behavior of Nd-Fe-B materials to realize the high-energy-product magnets.[14] When Nd-Fe-B ternary alloy phase diagram is analyzed, it can be seen that the magnetically hard Nd2Fe14B phase is formed through peritectic reaction from liquid and the primary a-iron phase. When this reaction occurs, the Nd2Fe14B peritectic phase forms, and this phase surrounds the primary a-iron, and thus prevents from further peritectic reaction.[15] The primary a-iron is always present in the alloy. This leads to decrease in maximum energy product. Therefore, it is crucially important to decrease the primary a-iron phase content in the Nd-Fe-B alloy ingots. Large undercooling is one of the widely used processes to form the peritectic compounds without primary a-iron phase.[16]
Two major commercialized p
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