Papers by Keyword: Amorphous

Abstract: A new kind of nanocomposite rare-earth magnets of Nd2Fe14B/ α-Fe were prepared by melt-spinning method. Effects of alloying element and processing parameter on the microstructure and magnetic properties of nanocomposite materials have been investigated. Zr is effective to enhance coercivity of alloys because of a refinement of grains, so that in alloy of Zr content with 1.0 at% (Zr1.0) has the smallest grain size of 17 nm and therefore causes the highest intrinsic coercivity . Addition of Zr can also enhance the ability of amorphous-forming. The combination of adding of Zr and using a smaller diameter of the nozzle in the melt-spinning method is effective for the forming of amorphous structure. According to the MFM study, the length of the magnetic contrast in the alloy is much larger than the mean grain size. The large length corresponds to that of interaction domains(ID), which is related to the exchange coupling effect.

Abstract: The Mg65Cu25Gd10-xNdx (x=0 ~ 10) amorphous alloy rods with 3~6 mm in diameter were prepared by Cu-mold injection method. The thermal properties and mechanical properties of these amorphous alloys have been investigated by DSC, SEM with EDS capability, X-ray diffractometry (XRD) and Vickers hardness test. The XRD revealed that these entire as-quenched Mg65Cu25Gd10-xNdx alloy rods exhibit a broaden diffraction pattern of amorphous phase. A clear Tg (glass transition temperature) and supercooled region (about 30~60 K) were revealed for all of those Mg65Cu25Gd10-xNdx alloys. In addition, the single stage crystallization of the Mg65Cu25Gd10 alloy was found to change into two stages crystallization when the Nd element was added into this alloy. In parallel, the crystallization temperature (Tx) and supercooled region (
Tx) presents a decreasing trend with increasing Nd content. The lowest liquidus temperature (Tl, about 721 K) occurs at the Mg65Cu25Gd8Nd2 alloy. In addition, The Mg65Cu25Gd8Nd2 alloy exhibits the high γ value (0.416, defined as γ= Tx/Tg+Tl), a relatively high Trg (0.59, defined as Trg = Tg/Tl) and the highest hardness in these alloys.

Abstract: XAFS measurements of the Cu, Ni and Zr K-edges for the melt-quenched Zr67Cu33 and Zr67Ni33 metallic glasses were curried out using synchrotron radiation at 20K. Fitting calculations for the EXAFS results reveal that local structure around Ni and Zr in Zr67Ni33 is well represented by those for the crystalline Zr2Ni, while local structure around Zr in Zr67Cu33 is better fitted by an icosahedron rather than crystalline Zr2Cu. Such differences of the local structure attribute to the differences of the stability of super-cooled liquid state and glass formability between Zr67Cu33 and Zr67Ni33 metallic glasses.

Abstract: Mg-based composites are fabricated through mechanical alloying (MA) the Mg65Cu20Y10Ag5 amorphous alloy spun and mixed with 1-5 vol.% spherical nano-sized ZrO2 particles in the planetary mill, after then formed by hot pressing in Ar atmosphere under different pressures at the temperature 5 K above the glass transition temperature (Tg). The microstructure characterizations of the resulting specimens are conducted by means of XRD, FEG-SEM, and TEM techniques. It is found that the nano-sized ZrO2 dispersed Mg-based composite alloy powders can reach to a homogeneous size distribution (about 80 nm) after 50-hour mechanical alloying. After hot pressing of these composite alloy powders under the pressure of 1100 MPa at 409K, a 96% dense bulk specimen can be formed. Throughout the MA and hot pressing, the amorphous nature of the Mg65Cu25Y10Ag5 matrix is maintained. The hardness of the formed bulk Mg-based composites (with 3 vol.% nano-sized ZrO2 particles) can reach to 370 in Hv scale. In addition, the toughness of the formed bulk Mg-based composites presents an increasing trend with the content of nano-sized ZrO2 particles and can reach to 8.9 MPa m .

Abstract: Application of TiNi shape memory alloy in biomedical field is rapidly expanding. Some of the applications calls for non-conventional properties, which may require new methods of thermomechanical treatment and surface modification. In the present study, the effect of nanocrystallization/amorphization by various method of severe plastic deformation, such as, shot peening, cold rolling and high pressure torsion, was investigated on properties of TiNi shape memory alloys. Shot peening using iron based metallic glass media was found to be an effective method to obtain the amorphous surface. Surface amorphization improved the corrosion resistance. Nanocrystalline TiNi exhibited peculiar superelastic properties. Correlation between the microstructure and phase transformation in nanostructured TiNi was discussed.

Abstract: Barkhausen noise properties of amorphous and nanocrystallized FINEMET type soft magnetic materials are investigated. It is obtained that the amorphous-nanocrystalline tranformation has a well observable effect on both the root main square, RMS, values and the critical exponents of the probability distributions of peak heights and durations.

Abstract: The magnetic inductance of nanocrystalline Fe73Si16B7Nb3Cu1 and an amorphous FeSiB sheet has been investigated to identify the radiofrequency identification (RFID) performance. Planar flow cast amorphous ribbons were pulverized and classified using a stack of sieve. The powder was mixed with binder and solvent and tape-casted to form 0.6-0.8 mm thick films. The inductance of the sheet was measured to investigate the RFID characteristics of the nanocrystalline and the amorphous materials. Results showed that the atmosphere for annealing significantly influenced on the inductance of the material. The surface oxidation of the particles was the main reason for the reduced inductance. The maximum inductance of Fe73Si16B7Nb3Cu1 alloy was about 88μH at 17.4 MHz, which was about 65% greater compared to the amorphous FeSiB alloy. The higher inductance in the nanocrystalline alloy indicates that it may be used as a potential replacement of current RFID materials.

Abstract: In this study, rod type Cu54Ni6Zr22Ti18 bulk amorphous alloy fabricated by warm extrusion of amorphous powders was investigated. To get bulk type amorphous alloy, the Cu54Ni6Zr22Ti18 amorphous powders which has a particle size below 63( and wide supercooled liquid region of 53K were prepared by a high-pressure gas atomization method. The powders were filled in a Cu can with an inner dimension 20×2×50mm in air, evacuated, sealed and then precompacted in the press. Before extrusion, the billet was heated with heating rate of 50K/min and the holding time was about 5min. The extrusion temperature was 723K and the extrusion ratio was increased from 2 to 5. By warm extrusion of amorphous powders, a fully amorphous Cu54Ni6Zr22Ti18 bulk type alloys were successfully synthesized. The conditions for extrusion were decided based on the time-temperature-transformation curve and DSC analysis. Phase analysis was performed by XRD. The result of the phase analysis indicated that Cu54Ni6Zr22Ti18 bulk rod type samples having fully amorphous phase could be obtained until extrusion ratio of 4 at extrusion temperature of 723K, but partial crystalline phase would be observed in the bulk rod type alloy fabricated at extrusion ratio of 5.

Abstract: Ti-Cu-Ni-Sn quaternary amorphous alloys of Ti50Cu32Ni15Sn3, Ti50Cu25Ni20Sn5, and Ti50Cu23Ni20Sn7 composition were prepared by mechanical alloying in a planetary high-energy ballmill (AGO-2). The amorphization of all three alloys was found to set in after milling at 300rpm speed for 2h. A complete amorphization was observed for Ti50Cu32Ni15Sn3 and Ti50Cu25Ni20Sn5 after 30h and 20h of milling, respectively. Differential scanning calorimetry analyses revealed that the thermal stability increased in the order of Ti50Cu32Ni15Sn3, Ti50Cu25Ni20Sn5, and Ti50Cu23Ni20Sn7.

Abstract: TiO2 nanoparticle was synthesized by the flame method using a metal organic precursor of titanium tetraisopropoxide (TTIP, Ti(OC3H7)4), which was controlled by varying the ratio and flow rate of gas mixtures consisting of oxygen (oxidizer), methane (fuel) and nitrogen (carrier gas). The morphology and the size distribution of nanoparticles were observed with TEM and FESEM, and the phase evolution was analyzed by XRD measurement using a monochromator. The crystalline phases of TiO2 nanoparticle depended strongly on the temperature distribution in the flame, whereas the morphology was not sensitive. During the flame synthesis of TiO2 nanoparticle, anatase TiO2 nanoparticle was predominantly synthesized at the high flame temperature and rapid flame cooling condition. The low flame temperature and long flame length enabled to form almost rutile TiO2 nanoparticle (>95%). The anatase nanoparticle was formed by a homogeneous nucleation and has finally kept the anatase phase without the phase transformation any more in the flame. However, the rutile TiO2 nanoparticle was not formed directly and homogeneously in flame, and was manufactured by the phase transformation such as amorphous
anatase
rutile. It was proved that the rutile phase was nucleated heterogeneously from the amorphous or anatase particles.