Structural and mechanical properties of graded composite Al2O3/Ni obtained from slurry of different solid content

AbstractIn this work, an alumina-nickel graded hollow cylinders were prepared by the centrifugal slip casting. In the paper, the results for samples formed from slurries with different solid content: 45 vol.%, 40 vol.% and 35 vol.% are presented. The structure of the samples after sintering was examined by X-ray diffraction (XRD). The microstructure of the composite, especially the nickel particle size distributions were investigated by using scanning electron microscopy (SEM). An image analyzer has been used for the measurement of volume fraction of the nickel particles in the composites. The hardness was measured by using a Vickers hardness-testing. Based on hardness measurements KIC value were determined. The XRD results confirmed only two phases: Ni and α-Al2O3 in all samples. The preliminary macroscopic observation as well as SEM showed, that the microstructure of the sample cross-section is not homogeneous. Microstructural characterization revealed the gradation of nickel content along the radial direction of hollow cylinder. Three zones were distinguished, from outer surface towards the inner side of the tube. The maximum of volume fraction of nickel particles was obtained at the middle zone of the composites. The results of hardness-testing revealed that the maximum hardness values were observed in region at the inner edge of the casting due to an absence of nickel particles

Magnetization Reversal Processes in the Nanocrystalline Fe-Co-Zr-Ti-Pr-B Magnets

Magnetization reversal processes in the magnets derived from the Fe 60 Co 13 Zr 1 Ti 3 Pr 9 B 14 alloy were investigated. It was shown that the processing technique affects the magnetization reversal processes. For the nanocrystalline ribbon samples pinning of the domain walls arises at low external magnetic fields while nucleation of reversed domains occurs at higher fields. However, the nucleation fields are lower than the pinning fields for the nanocrystalline rod and tube samples produced by suction-casting technique

Magnetic Properties of Nd12Fe82B6Nd_{12}Fe_{82}B_6 and Nd14Fe80B6Nd_{14}Fe_{80}B_6 Powders Obtained by High Temperature Milling

The present paper describes a comparison of magnetic properties of $Nd_{12}Fe_{82}B_6$ and $Nd_{14}Fe_{80}B_6$ powders obtained by a new method of processing of Nd-Fe-B powders - high temperature milling. In this method the milling operation is carried out, entirely or only in the final stage, at high temperatures, so that the destruction of the $Nd_2Fe_{14}B$ phase and its recombination occur simultaneously. In this way a powder with good magnetic properties immediately after milling was obtained. In the present experiments, the powder was subjected to high-energy milling for 17 h (until the material becomes amorphous) and then, the milling was continued for 0.5 h with the powder container being heated to an appropriate temperature or milled at high temperature during whole time of the process. Diffraction examinations have shown that the powder processed in this way contains the $Nd_2Fe_{14}B$ phase. Its magnetic properties appear to depend on the applied temperature or milling time (at optimum temperature). The used method of processing leads to obtaining high-coercivity Nd-Fe-B powders. The magnetic properties of the material thus produced, in particular its coercivity, strongly depend on the milling temperature and milling time

Characterization of Selected Parameters of Organic-Inorganic Hybrid Membranes Based on Various Polymers and Nd-Fe-B Fillers

In this paper magnetic organic-inorganic hybrid membranes based on EC, PPO polymer matrices and various magnetic powder microparticles were synthesized and studied. Constant pressure permeation technique and the Time Lag method were used to obtain the gas transport coefficients. The mechanical, rheological and magnetic parameters of magnetic hybrid membranes were examined. It was found that their separation and gas transport properties (D, P, S and α) were improved with the decrease in powder particle size and the increase of membrane’s remanence, saturation magnetization and magnetic particle filling. The increase of the magnetic powder addition and a decrease of its granulation improved also mechanical and rheological parameters of the tested membranes. This improvement also had a positive effect on their gas separation properties and their potential usage in the future

Characterization of Selected Parameters of Organic-Inorganic Hybrid Membranes Based on Various Polymers and Nd-Fe-B Fillers

In this paper magnetic organic-inorganic hybrid membranes based on EC, PPO polymer matrices and various magnetic powder microparticles were synthesized and studied. Constant pressure permeation technique and the Time Lag method were used to obtain the gas transport coefficients. The mechanical, rheological and magnetic parameters of magnetic hybrid membranes were examined. It was found that their separation and gas transport properties (D, P, S and α) were improved with the decrease in powder particle size and the increase of membrane’s remanence, saturation magnetization and magnetic particle filling. The increase of the magnetic powder addition and a decrease of its granulation improved also mechanical and rheological parameters of the tested membranes. This improvement also had a positive effect on their gas separation properties and their potential usage in the future

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

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

Magnetization Reversal Processes in the Nanocrystalline Fe-Co-Zr-Ti-Pr-B Magnets

Magnetization reversal processes in the magnets derived from the $Fe_{60}Co_{13}Zr_1Ti_3Pr_9B_{14}$ alloy were investigated. It was shown that the processing technique affects the magnetization reversal processes. For the nanocrystalline ribbon samples pinning of the domain walls arises at low external magnetic fields while nucleation of reversed domains occurs at higher fields. However, the nucleation fields are lower than the pinning fields for the nanocrystalline rod and tube samples produced by suction-casting technique

Zależność mikrostruktury i właściwości magnetycznych od grubości magnesów Nd60Fe30Al10 odlewanych w postaci płytek

The hard magnetic Nd-Fe-Al alloys are inferior to Nd-Fe-B magnets as far as the magnetic properties are concerned, but their great advantage is that they need no additional annealing to achieve good magnetic properties. These properties depend on the cooling rate from the melting state, and on the thickness of the sample - the best values are achieved at the quenching rates at which the samples have a thickness of 0.3-2 mm. The present study is concerned with the correlation between the magnetic properties of the plate-shaped Nd60Fe30Al10 samples and their size - thickness. Two casting ways: with the melt stream perpendicular direction and parallel to the surface of the plates were used. The plates were produced by pressure casting and suction casting. The studies have shown that the cooling rates depends on local propagation on liquid metal in the mold resulting in heterogeneity of structure and properties.Stopy Nd-Fe-Al nie posiadają tak wysokich właściwości magnetycznych jak Nd-Fe-B. Ich dużą zaletą jest natomiast możliwość otrzymywania bezpośrednio poprzez odlewanie. Właściwości magnetyczne zależą od szybkości chłodzenia ciekłego stopu, co w praktyce określa się rozmiarem odlewanej próbki. Przy odlewaniu do form metalowych optymalny zakres wymiaru w kierunku odprowadzania ciepła to 0,3-2 mm. W niniejszej pracy zbadano zależność właściwości magnetycznych stopu Nd60Fe30Al10 od grubości próbek w postaci płytek w zależności od sposobu odlewania (wtryskiwanie cieczy pod ciśnieniem i odlewanie z zasysaniem) oraz kierunku strumienia cieczy (prostopadle lub równolegle do powierzchni płytki). Badania wykazały, że szybkość chłodzenia zależy lokalnie od sposobu rozchodzenia się cieczy w formie, co skutkuje niejednorodnością mikrostruktury i właściwości

Wysokokoercyjne proszki Nd-Fe-B otrzymywane przez mielenie w wysokiej temperaturze

The possibility of employing high temperature milling (600°C) for the production of highly coercive Nd-Fe-B powders was examined. The materials were the Nd12Fe82B6, alloy which was subjected to mechanical milling and the powders of the constituent elements of this alloy which were processed by mechanical alloying. The processes were conducted in the two variants: the first variant consisted of mechanical milling performed at a high temperature which was maintained during the entire process, and the other variant included preliminary milling carried out at room temperature and then the milling temperature was increased. All the processes gave nanocrystalline powders with hard magnetic properties. The powders produced by mechanical milling had better properties than those produced by mechanical] alloying as they were more homogeneous and contained smaller amounts of the α-Fe phase.W pracy badano możliwości zastosowania procesu mielenia w wysokiej temperaturze (600°C) do otrzymywania wyso- kokoercyjnych proszków Nd-Fe-B. Mieleniu poddano stop Nd12Fe82B6,. a także zastosowano metodę mechanicznej syntezy stopów tzn. mielono proszki pierwiastków składników stopu. Procesy prowadzono w dwóch wariantach: cały proces odbywał się w podwyższonej temperaturze lub stosowano wstępne mielenie w temperaturze pokojowej, a następnie mielenie w wysokiej temperaturze. We wszystkich procesach uzyskano nanokrystalicze proszki o właściwościach magnetycznie twardych Proszki uzyskane w procesie mielenia stopu miały właściwości lepsze od proszków otrzymanych w procesie mechanicznej syntezy stopów, ponieważ były bardziej jednorodne i posiadały mniejszy udział fazy α-Fe

High-coercivity Nd-Fe-B Powders Obtained by High-Temperature Milling

The possibility of employing high temperature milling (600°C) for the production of highly coercive Nd-Fe-B powders was examined. The materials were the Nd12Fe82B6, alloy which was subjected to mechanical milling and the powders of the constituent elements of this alloy which were processed by mechanical alloying. The processes were conducted in the two variants: the first variant consisted of mechanical milling performed at a high temperature which was maintained during the entire process, and the other variant included preliminary milling carried out at room temperature and then the milling temperature was increased. All the processes gave nanocrystalline powders with hard magnetic properties. The powders produced by mechanical milling had better properties than those produced by mechanical] alloying as they were more homogeneous and contained smaller amounts of the α-Fe phase.W pracy badano możliwości zastosowania procesu mielenia w wysokiej temperaturze (600°C) do otrzymywania wyso- kokoercyjnych proszków Nd-Fe-B. Mieleniu poddano stop Nd12Fe82B6,. a także zastosowano metodę mechanicznej syntezy stopów tzn. mielono proszki pierwiastków składników stopu. Procesy prowadzono w dwóch wariantach: cały proces odbywał się w podwyższonej temperaturze lub stosowano wstępne mielenie w temperaturze pokojowej, a następnie mielenie w wysokiej temperaturze. We wszystkich procesach uzyskano nanokrystalicze proszki o właściwościach magnetycznie twardych Proszki uzyskane w procesie mielenia stopu miały właściwości lepsze od proszków otrzymanych w procesie mechanicznej syntezy stopów, ponieważ były bardziej jednorodne i posiadały mniejszy udział fazy α-Fe