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Consolidation of Nanocrystalline Nd-Fe-B Powder by Hydrostatic Extrusion at High Temperature

100%

Gizynski T., Kaszuwara W., Kulczyk M., Leonowicz M.

Acta Physica Polonica A

2017

vol. 131

issue 5

1260-1263

Hydrostatic extrusion is a modern method of shaping material microstructure and properties. Hydrostatic extrusion can also be successfully used for consolidation of hard magnetic powders. The effect of extrusion temperature, within the range of 700-800°C, on the magnetic properties of the bulk, final product was studied. A commercial MQU-F42 powder, dedicated to hot pressing, was placed in copper capsules and initially cold compacted up to 60% of the theoretical density. Subsequently, the billet was heated in an oven to temperatures 700 and 800°C, respectively and subjected to hydrostatic extrusion. The extruded product had a form of a copper rod, with the Nd-Fe-B core, having 96% of theoretical density (true strain 1.85 after extrusion at 800°C). The extrusion process led to deterioration of the coercivity, for which coarsening of the Nd₂Fe₁₄B grains was blamed. In order to prove this hypothesis, the starting powder was annealed in a temperature range of 550-900°C for various times. The crystallite size, measured after annealing by the X-ray diffraction method, showed that with extension of time and elevation of the temperature the crystallite size increases, however the dominating parameter is the temperature. Correlation of the crystallite size with temperature indicates that when the crystallites are larger than 80 nm the magnetic properties dramatically decrease. Additionally, after HE at 800°C micrometric size Nd-rich phase appear in the microstructure. The Nd is squeezed from the grain boundary of the Nd₂Fe₁₄B phase leading to non-isolated grains, which also contributes to the deterioration of the coercivity.

Microstructure and Properties of Magnets Obtained by Hydrostatic Extrusion of Nd-Fe-B Powder

76%

Gizynski T., Kaszuwara W., Pawlik P., Kulczyk M., Leonowicz M., Michalski B.

Acta Physica Polonica A

2015

vol. 127

issue 2

626-628

Nd-Fe-B MQ powder was initially densified in a copper capsule to reach about 60% of the theoretical density. Subsequently, three various processes of hydrostatic extrusion were conducted at room temperature. The values of true strain, obtained during the all three stages, were 1.38, 0.89, 0.94, respectively. The investigation performed showed that the coercivity of the material decreases as the strain increases. Decrease of the remanence was observed only for the highest strains. Size of the particles was strongly reduced during the extrusion processes. X-ray diffraction did not show changes in the phase structure of the material. The Mössbauer study, of the sample extruded within all the three stages, showed existence of the Nd₂Fe₁₄B phase and 16% of other phase. Analysis of magnetization versus temperature confirmed that the additional phase was ferromagnetic.

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2 Acta Physica Polonica A

1 2017

1 2015

2 Gizynski T.

2 Kaszuwara W.

2 Kulczyk M.

2 Leonowicz M.

1 Michalski B.

1 Pawlik P.

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Consolidation of Nanocrystalline Nd-Fe-B Powder by Hydrostatic Extrusion at High Temperature

Microstructure and Properties of Magnets Obtained by Hydrostatic Extrusion of Nd-Fe-B Powder