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Abstract
The thermal stability of milling Fe86Zr11-xNbxB3 (x = 5.5, 6) melt-spun strip powders and the influence of high-pressure sintering conditions on phase component and grain size of bulk alloys were investigated by X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The results show that milling melt-spun powder remains in the amorphous state, and the crystallization temperature of which is 480-530°C, the apparent activation energy Ep of crystallization process is 294.1-219.5 kJ/mol. The increasing Nb content can increase crystallization temperature and decrease Ep. Under the sintering conditions of 5.5 GPa/3 min, when Pw is 1150 W, single phase α-Fe nanocrystalline (20.6-26.7 nm) bulk alloy with relative density higher than 99.0% can be obtained. Under the sintering conditions of 5.5 GPa/1150 W/3 min, the magnetic properties of these nanocrystalline bulk alloys are Fe86Zr5.5Nb5.5B3 alloy, Bs = 1.15 T, Hc = 5.08 kA·m-1; Fe86Zr5Nb6B3 alloy, Bs = 1.26 T, Hc = 4.27 kA·m-1.
Global demand for bone grafts has been increasing rapidly in recent years. In particular, an increase in the elderly population worldwide at an annual rate of more than 5% has led to a rapid increase in the bone-diseased population because the elderly suffer easily from osteoporotic fractures, degenerative scoliosis, and degenerative spondylolisthesis [1]. Bone is a complex biomineralized organ with an intricate hierarchical microstructure assembled through the deposition of apatite minerals on collagenous matrix [2], and is able to self-heal a small defect. However, the self-healing is less effective for a large defect. For this, bone grafting is required in orthopaedic surgery. Bone grafting is a surgical procedure that introduces new bone or a substitution material (bone graft) into defects in bone or around broken bone to help bone healing. Depending on the source of bone grafts, they may be roughly divided into autologous bone grafts (autografts), allografts and artificial (synthetic) bone grafts. These bone grafts have their own particular advantages and drawbacks. Theoretically, an autograft should be the best choice because the bone graft is the patient's own bone, taken frequently from his/her hip bone or pelvis, which renders clear advantages such as a mechanical match with the damaged bone, excellent osteogenic potential, and immune safety [3]. Nevertheless, the principal disadvantage of using autograft bone is that the patient needs to bear additional chronic pain at the incision site, runs potential risks such as infection, additional blood loss, and morbidity, and must bear a longer operation duration and higher costs [4]. Therefore, the other approaches are becoming popular.
Glass-coated amorphous FeCuNbSiB microwires were prepared by Taylor-Ulitovsky technique. X-ray diffractometry and scanning electron microscopy were used to investigate the microstructure and morphology of the glass-coated microwires respectively. The vibrating sample magnetometer and vector network analyzer were used to study the magnetostatic and microwave properties of glass-coated microwires. The experimental results show that the effective anisotropy of an array of 150 microwires of 10 mm in length is large than that of one microwire of 10 mm in diameter and an array of 150 microwires of 1 mm in diameter. The natural ferromagnetic resonance takes place as the microwave magnetic component is perpendicular to the microwires axis, and the electric dipole resonance takes place as the microwire is long or the short microwire concentration is moderate. The natural ferromagnetic resonance shifts to higher frequency with the larger microwire concentration. The electric dipole resonance is governed by the microwires length and concentration. The glass-coated FeCuNbSiB microwires can be used to design EMI filters and microwave absorbing materials.
Due to large grain sizes, the biological properties of the conventional calcium phosphate (Ca–P) bioceramics are limited to a great extent. Progresses in nanotechnological approaches now allow the fabrication of nanocrystalline Ca–P bioceramics. In this article we first review current methodologies of the Ca–P nanocrystal syntheses and nanoceramic processes. In particular, we emphasize in this article the fabrication of porous Ca–P nanoceramics using a modified co-precipitation synthesis and its microwave sintering. Subsequently, the biological properties of the three-dimensional porous Ca–P nanoceramics, involving protein adsorption, cell adhesion, bone repair, osteoconductivity and osteoinductivity, are introduced in detail on the basis of the in vitro protein adsorption and cell adhesion, and in vivo intramuscular and bone implant experiments. Because of high specific surface area, nano-level surface topography, high surface defects and interconnecting macropores with abundant micropores, the Ca–P nanoceramics can well initiate and regulate a cascade of gene activities of cells, thereby resulting in higher in vivo osteoconductivity and osteoinductivity than the conventional ones. Finally, the degradability, potential risk, and anticancer activity of the nanoceramics are discussed. In summary, because of the chemical and macro-/nanoscale structural similarities with bone, the Ca–P nanoceramics are hopeful of becoming a new generation of biomaterials for hard tissue repair.
Amorphous (Fe0.99, Mo0.01)78Si9B13 alloys were annealed for 30min at a temperature between 600K and 930K under pressures of normal pressure to 7GPa. It was found that precipitation temperature of their crystallization products of α-Fe (Mo, Si), Fe3B and Fe2B alloys are related closely to the pressure used. Crystallization temperature of amorphous alloy and precipitation temperature of the metastable phase Fe3B decrease with increasing pressure at the present pressure condition. At certain temperature and pressure, the Fe3B alloy will transform into a stable phase Fe2B and its transition temperature change with pressure. A thermodynamic mechanism on the crystallization of the amorphous (Fe0.99, Mo0.01)78Si9B13 alloy and the phase transition of the Fe3B to the Fe2B was discussed, and an equation of the phase transition from the Fe3B to the Fe2B was given.
Fe73.5Cu1Nb3 Si13.5B9 soft magnetic alloy powders and its bulk alloys were prepared by the mechanical alloying (MA) method and cryogenical high pressure solidification process. Phase components, average grain size, thermal stability of powders and relative density of bulk alloys of the samples were analyzed by XRD, DSC, SEM and TEM. The results showed that (1) after MA for 70 hours, bcc single phase α-Fe nanocrystalline supersaturate solid solution powders with average grain size 9.5 nm can be obtained; (2) four exothermal peaks with different intensity appeared in DSC heating-up curves, these peaks corresponded to structural relaxation of distorted nanocrystalline supersaturate solid solution, crystallization of small quantity amorphous and phase precipitation of supersaturate solid solution, respectively. Phase precipitation of supersaturate solid solution included two stages; (3) under the sintering conditions of P = 5.5 GPa, t = 5 min and PW = 980 W, single phase α-Fe nanocrystalline bulk alloys with 98.4% relative density and about 12.5 nm average grain size can be obtained, soft magnetic properties of the bulk alloys were specific saturation magnetization Ms = 1.71 × 10-7 Wb·m/g, coercive force Hc = 8.22 × 103 A/m.
Fe65Co10Ga5P12C4 B4 glassy alloy powders were produced by high pressure Ar gas atomization of Fe65Co10Ga5P12C4 B4 alloy ingot prepared by induction melting. The glass transition temperature (Tg), supercooled liquid region (ΔTx (=Tx-Tg)) of the glassy alloy powders are 730K and 50K. The glassy alloy powders have ferromagnetism with a Curie temperature (Tc) of 640 K and exhibits saturation magnetization (I2) of 1.18T. No appreciable difference in the thermal stability and magnetic properties is seen between the glassy alloy powders and the melt-spun ribbon. By spark-plasma-sintering (SPS) these glassy alloy powders under the pressure of 80 MPa and at the temperature of 723 K below Tg, a bulk glassy Fe65Co10Ga5P12C4 B4 alloy with a size of 20 mm in diameter and 5 mm in thickness was synthesized. Its relative density was about 96%. There was also no appreciable difference in the thermal stability between the bulk glassy alloy and the glassy alloy powders. This bulk glassy alloy exhibited saturation magnetization (I2) of 1.19T and coercivity (Hc) of 115 A/m.
Nanocrystalline bulk Fe90Zr7B3 alloys with grain sizes of 20 to 30 nm were prepared by spark-plasma sintering of amorphous powders and subsequent annealing. The bulk alloys sintered at the temperature (Ts) between 673 and 723 K are composed of a mostly single amorphous phase and the alloy sintered at Ts of 873 K is composed of a mostly single bcc-Fe phase in as-sintered state. The former alloys show better soft magnetic properties in spite of porous consolidated state than the latter alloy after annealing at 923 K. For the bulk alloy sintered at Ts of 723 K, the effective permeability (μc) increases by accelerating the heating rate (α) in sintering and the density becomes higher by increasing the sintering pressure (Ps). The nanocrystalline alloy sintered at Ts of 723 K, Ps of 780 MPa and α of 1.7 K/s shows the maximum permeability of 29800, effective permeability of 3430 at 100 Hz and coercivity of 12 A/m with a relative density of 97 %.
Dynamic compaction of amorphous Fe//8//0P//1//6C//4 powder produced by rapid quenching water atomization was performed using a gun accelerator. The effect of shock duration time on magnetic properties has been investigated by means of X-ray diffraction analysis, microhardness tests, optical microscopy, scanning electron microscopy and magnetic measurements. The results indicate that the magnetic properties can be described by a change in the atomic short-range order which is caused by shock pressure and temperature.
A bulky Fe84Nb7B, alloy was obtained by extruding the powders ground from amorphous ribbon, at temperatures T(e) between 563 K and 723 K at pressures P(e) between 824 MPa and 1208 MPa and at a speed of 5 mm s-1. The bulk Fe84Nb7B9 alloy extruded at T(e) = 698 K and P(e) = 1208 MPa is in a fully consolidated state and has a density of about 99%. The bulk alloy is composed of a mostly single b.c.c. phase with a grain size of about 10 nm after annealing for 3.6 ks at temperatures between 873 K and 973 K, and its soft magnetic property tends to be better for the bulks extruded at lower pressures. The bulk alloy extruded at T(e) = 698 K and P(e) = 824 MPa exhibits a high saturation magnetization B(s) of 1.40 T and a low coercive force H(c) of 64 A m-1 after annealing at 698 K.
Improvement in warm extrusion processing have been made to prepare bulk amorphous alloys from amorphous alloy powders. Flake-form amorphous alloys of Fe78B13Si9 and Co69Fe4Ni1Mo2B12Si12 were used. When a billet of powder, packed into a cylindrical container, was extruded, a completely homogeneous bulk amorphous alloy was not obtained. However, when a core of suitable material and diameter was placed along the central axis of the container, a homogeneous bulk amorphous alloy was obtained by extruding the billet under certain specific conditions. The compacts obtained, moreover, had a density equal to 99.9% that of ribbon, and the magnetic properties were the best so far reported for bulk amorphous alloys. In this paper, the effects of different process conditions on compactibility are also discussed.
Until now, there have been no reports in which bulk amorphous alloys of the same densities as those of the corresponding ribbons had been successfully prepared from the amorphous alloy powders by static pressure. Because of the fact that the crystallization temperature Tx of amorphous alloys increased under a high pressure, measurements of Tx on Fe78B13Si9 alloy under pressure were carried out, and it was confirmed that Tx for the alloy rose at a rate of about 10 K GPa−1. Using this phenomenon, amorphous alloy powder of Fe78B13Si9 was compacted at temperatures just below Txh (Tx under a high static pressure) at 5.4 GPa. As a result, we could prepare bulk amorphous alloys with the same densities as those of the corresponding ribbons; it was not possible to prepare these alloys by high pressure compaction below Txo (Tx under ordinary pressure). Most of the physical properties of the compacts were similar to those of the ribbons.