Structural, magnetic, and mechanical hardness characterization of the alloy Nd16(Fe76−xNix)B8 with x = 0, 10, 20, and 25

Abstract

In this work, samples of the alloy Nd16 (Fe76−x Nix) B8 with x = 0, 10, 20, and 25 were produced by arc melting under an Ar atmosphere and heat treated at 1073 K during 30 min, and then quenched in ice–water mixture. X-ray diffraction (XRD), Mossbauer spectroscopy (MS), and vibrating sample magnetometry (VSM) were used to characterize the properties of the obtained samples. Microhardness tests were performed too. XRD results found Nd2Fe14B and Nd1.1Fe4B4 as main phases. It is found for x = 0, 10, 20, and 25, lattice parameters a and c, and the volume of Nd2Fe14B and Nd1.1Fe4B4 phases, which decrease with the increase of nickel content. The parameter a of the Nd1.1Fe4B4 phase has a tendency to increase in value compared to the parameter c which has a tendency to decrease with the concentration of nickel; this behavior causes the lattice to dilate in a and it is compressed in c, indicating that Ni atoms are preferably entering along c. The two phases parallel to crystallite sizes are greater than the perpendicular ones, indicating that the crystallite shape is not spherical but elongated in that direction. XRD results for all samples doped with Ni indicate that the crystallite sizes are of the nanometer order and range between 5 and 90 nm. It is evident the addition of this element does not damage the structural formation of Nd2Fe14B phase. MS shows seven magnetic sites (16k1, 16k2, 8j1, 8j2, 4c, 4e, and sb d) and a paramagnetic phase (doublet) corresponding to the phases found by XRD. The mean hyperfine magnetic field of the samples decreases with the increase in the concentration of Ni. According to the decrease of the percentage of the area and the hyperfine magnetic field of 16k2, 8j2, and 4c sites’ phase Nd2Fe14B in Ni-doped samples, preference of nickel atoms to replace iron atoms at these sites was established. It can see also the relative area of the site d (Nd1.1Fe4B4) which decreases with Ni concentration. VSM results showed that the major phase Nd2Fe14B is the hard magnetic phase, while the paramagnetic phase Nd1.1Fe4B4 is the minority phase. There is a general trend of microhardness increase with nickel content, attributable to nickel doping which reduces the lattice parameters and porosities in the sample improving its hardness.