Abstract

Using scanning electron microscopy (EDS analysis), magnetic force microscopy, and nanoindentation, a metallographic study of the magnetic structure and nanomechanical properties of sintered rare-earth magnets Nd–Dy–Fe–B of the USC-20L brand has been carried out (Ural Strip Casting Technology). The microstructure of the sintered Nd–Dy–Fe–B magnet of the USC-20L grade includes the following components: grains of the Nd₂Fe₁₄B phase are separated by lamellas of the phases enriched in neodymium. Inclusions Nd–29.1% Fe–6.2% C–2.2% O–1.4% Dy are located at the triple junctions of Nd₂Fe₁₄B grains. Inclusions Nd–4.5% Fe–9.1% O–6.7% C–4.5% Fe–2% Dy are along grain boundaries containing Nd and Dy oxides. The chemical composition of grains is Fe–25% Nd–6.9% C–1.6% Dy–1.4% B. It is found that, due to irregular grain growth, the interlayers of the enriched Nd phase are connected to each other in the region of grain junctions, causing a concentration of internal stresses and the appearance of a crack. The crack propagates along the grain boundary from one wetted joint of the grains to another, due to mechanical stresses. The phenomenon of intergranular wetting by a phase of Nd-enriched Nd₂Fe₁₄B/Nd₂Fe₁₄B grain boundaries is observed. It has been established that phases enriched with Nd can pseudo-incompletely (or pseudo-partially) wet such grain boundaries, i.e., form a nonzero contact angle along the grain boundaries and in triple joints. Based on the results of Magnetic Force Microscopy (MFM), a conclusion is made about the presence of a one-dimensional domain structure; domains cross grain boundaries. The presence of pores and inclusions of Nd and Dy oxides localized along grain boundaries is noteworthy. The average transverse domain size of the banded structure is ~1 μm, the energy of the domain wall γ ~ 14 kJ/m², and the width of the domain wall δ ~ 0.6 × 10^–9 m. The nanoindentation method is used to measure the values of nanohardness (H, GPa), elastic modulus (E, GPa), contact stiffness (S, N/m), elastic work (W_e, nJ) and plastic strain (W_p, nJ) in submicrovolumes of Nd₂Fe₁₄B grains. According to the measurement results, the minimum value of Nd₂Fe₁₄B grain adhesion K_int = 0.539 MPa m^0.5 is estimated.

中文翻译：

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烧结永磁体Nd-Dy-Fe-B USC-20L的磁性结构和纳米力学性能

摘要

利用扫描电子显微镜（EDS分析），磁力显微镜和纳米压痕，对USC-20L品牌的烧结稀土磁体Nd-Dy-Fe-B的磁性结构和纳米机械性能进行了金相研究（乌拉尔带钢铸造技术）。USC-20L级Nd-Dy-Fe-B烧结磁体的微观结构包括以下成分：Nd ₂ Fe ₁₄ B相的晶粒被富钕相的薄片隔开。夹杂物Nd–29.1％Fe–6.2％C–2.2％O–1.4％Dy位于Nd ₂ Fe ₁₄的三重结处B粒。夹杂物Nd–4.5％Fe–9.1％O–6.7％C–4.5％Fe–2％Dy沿含有Nd和Dy氧化物的晶界。晶粒的化学成分为Fe–25％Nd–6.9％C–1.6％Dy–1.4％B。发现，由于晶粒的不规则生长，富Nd相的中间层在该区域相互连接晶界处的裂纹，导致内部应力集中和出现裂纹。由于机械应力，裂纹沿着晶粒边界从晶粒的一个润湿的接头传播到另一个。富Nd ₂ Fe ₁₄ B / Nd ₂ Fe ₁₄相引起的晶间润湿现象观察到B晶界。已经确定，富含Nd的相可以伪不完全地（或伪部分地）润湿这种晶界，即，沿着晶界和在三重缝中形成非零接触角。根据磁力显微镜（MFM）的结果，得出关于一维畴结构的结论。区域跨越晶界。值得注意的是，沿晶界分布的孔和Nd和Dy氧化物夹杂物的存在是值得注意的。带状结构的平均横向畴尺寸为〜1μm，畴壁的能量为γ〜14 kJ / m ²，畴壁的宽度为δ〜0.6×10 ^–9 m。纳米压痕法用于测量纳米硬度（H（GPa），弹性模量（E，GPa），接触刚度（S，N / m），弹性功（W _e，nJ）和塑性应变（W _p，nJ）在Nd ₂ Fe ₁₄ B晶粒的亚微体积中。根据测量结果，估计Nd ₂ Fe ₁₄ B晶粒附着力的最小值K _int = 0.539 MPa m ^0.5。