Pressless process in route of obtaining sintered Nd-Fe-B magnets

A short review on the pressless process (PLP) involved in the manufacture of sintered Nd-Fe-B magnet is given. Two approaches to increasing the degree of powder alignment with a high filling density ρf in PLP-containers are proposed. (1) An increase in the pulse duration of applied magnetic field from 3.6 to 6.5 ms enhances the magnetic alignment of magnets prepared from the powder with ρf=2.5 g/cm3 and ρf=3 g/cm3 by 3% and 11%, respectively. (2) Addition of internal lubricants such as zinc stearate or esters reduces friction forces between the powder particles and, when the concentration of lubricants is bellow a critical concentration Ccr, increases Br and (BH)max by 5-7%. Simulation of the magnetic alignment of uniaxial particles demonstrates that a decrease in the coefficient of friction between the powder particles from 0.9 to 0.6 caused by the lubricant addition enhances the alignment degree. Contact dilatometry was used to study the anisotropy of densification of PLP-powders upon sintering. It has been shown that the anisotropy of the powder shrinkage is formed at the first stage of sintering at the temperature about 800 °С and is caused by the capillary action in the Nd-rich liquid.