The effects of mechanical milling on the structural, mechanical, and electromagnetic properties of Cu-8 wt% NdFeB composite alloys

Abstract

In an attempt to develop new materials that combine structural (mechanical) and functional (electrical and magnetic) properties, a copper composite alloy reinforced through the dispersion of fine Nd2Fe14B intermetallic particles has been synthesized by the powder metallurgy route. Composite master alloy was prepared by blending copper and 8 wt% of intermetallic NdFeB in a planetary ball mill working at 250 r/min under argon atmosphere for 10 h. Resulting composite powders were encapsulated in Cu cans and then consolidated by extrusion at 1023 K. Microstructure features of blended powders and consolidated materials were characterized by means of X-ray diffraction, scanning electron microscopy, and electron probe micro analysis. Fitting of the X-ray diffraction patterns with the Rietveld method revealed that during processing, some NdFeB particles reacted with copper and oxygen to form Nd2CuO4. The lower Nb content on the Nd2Fe14B intermetallic phase due to this oxidation causes the dispersion of Fe and Fe2B particles, which also have soft magnetic properties but a higher moment compared to Nd2Fe14B. The extruded alloys showed enhanced mechanical properties (with yield strength ≥ 600 MPa, ultimate tensile strength ≥700 MPa, and 5% elongation to failure) with satisfactory electrical conductivity (46% IACS) and high values of the coercive field (≥30,000 A/m).