Structural, magnetic and mechanical properties of Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 nanocrystalline hard magnet

Abstract

Microstructural, magnetic and mechanical properties of Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 nanocrystalline hard magnets produced by rapid solidification technique and subsequent thermo-magnetic annealing have been investigated in this study. X-ray diffraction analysis revealed that the as-cast Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 magnet has 60% Nd2Fe14B, 16% α-Fe, 9% Fe3B and 15% amorphous phases, whereby, Nd2Fe14B being the majority phase. Thermomagnetic annealing induces a complete crystallization of Nd2Fe14B, α-Fe, Fe3B and amorphous phases and establishes ideal volume fractions between phases leading to improvement in magnetic properties. Scanning and transmission electron microscopy show nano-scaled hard Nd2Fe14B grains surrounded with soft α-Fe and Fe3B grains. The Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 magnet annealed at 993 K for 15 min shows values of coercivity iHc, remanence Br and maximum energy product (BH)max up to 861 kA/m, 0.68 T and 81.9 kJ/m3, respectively. Compressional stress strain measurements elucidated that mechanical properties of alloys are affected by the morphology of phases as well as crystal structure. As-cast Nd6.8Fe63.3Nb4.0Co1.3Cr1.1Zr0.9B22.6 magnet demonstrates the hardness (Hv) of 960 ± 20 and compressive stress (σf) of 1270 ± 10 MPa, which tend to decrease by thermo-magnetic annealing process.