Development of bulk Nd9.5Fe75.5 − xMxB15 (M = Mo, Nb, Ta, Ti, and Zr; x = 0–4) magnets by direct casting method

Magnetic properties, phase constitutions and microstructure of directly quenched Nd9.5Fe75.5 − xMxB15 bulk magnets in rod form with a diameter of 0.7 mm have been studied. The substitution of the selected refractory elements can suppress Nd2Fe23B3 and one unknown phase, leading to the presence of the large amount of Nd2Fe14B phase. Besides, the grain size at the centre of the rods is refined from micrometer scale for a ternary magnet to 50–120 nm for the refractory element substituted magnets. Accordingly, the magnetic properties are improved remarkably from Br = 5.1 kG, iHc = 1.0 kOe and (BH)max = 1.7 MGOe for ternary Nd9.5Fe75.5B15 to Br = 6.5 kG, iHc = 10.3 kOe and (BH)max = 8.7 MGOe for Nd9.5Fe72.5Ti3B15 magnet.