Page 9 - Дисертація_Борух

9

It is proposed to use hydrogen for sintering powders of neodymium-iron-

boron alloys. The influence of compression pressure of powders and

recombination temperature during their sintering on the properties of sintered

materials is estimated. The sintering in hydrogen of powders with particles with

sizes ≈5-15 m and microstructure crushed to 0.5-3 m is investigated. Pressing is

2
performed at a pressure of 2 and 5 t/cm . Sintering conditions: hydrogen pressure
0.05 MPa, temperature 750°C. In both cases, the powder is sintered. Coarse

particles, up to ≈15 m, are surrounded by thin ones. The sintered material

contains regions with a ratio of components close by composition to stoichiometric

(Nd 2(Fe,Zr) 14B), α-Fe with a small amount of Nd and Zr, as well as a rich Nd

phase. The microstructure of coarse particles is inhomogeneous: the dark gray

layer along the particle boundaries is the products of Nd 2(Fe,Zr) 14B

disproportionation - NdHx, α-Fe and Fe 2B (in coarse particles the Nd 2(Fe,Zr) 14B

phase is partially disproportionated). That is, to obtain a homogeneous
microstructure of the sintered material, the powder must consist of highly

dispersed particles close in size. The material sintered under the same conditions,
2
after pressing at a pressure of 5 t/cm ,contains cavitation voids. It is established

that the microstructure of the products of disproportionation is highly dispersed.
With increasing pressure of the powder, the porosity of the sintered material is

significantly reduced.

The influence of desorption – recombination (DR) conditions on the

properties of sintered materials was investigated at temperatures of 850 and 950 C.
2
The powders were pressed at a pressure of 5 t/cm . After sintering, the materials

had a small number of cavitation voids. It is shown that the recombination

temperature affects the dispersion of the microstructure of the sintered material.

After recombination at a temperature of 850°C, the grain size of the Nd 2Fe 14B

phase is 50-80 nm, and after 950°C - 100-215 nm.

It is shown that with the increase of DR temperature to 950 C the number of

cavitation voids and their size increases to 0.7-1.5 μm. Qualitatively, the phase