Authors: Sung Chul Lim, Kyung Hoon Kim, Heung Bok Lee, Hyo Soo Lee, Hyouk Chon Kwon
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.
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Authors: Ge Wang, Chun Zhang, Yu Ying Zhu, Zhi Gang Chao, Qiang Li
Abstract: Ti50Fe45Sn5 amorphous alloys powder was prepared by mechanical alloying (MA) in a high-energy planetary ball mill. The non-crystallization degree was tested by X-ray diffraction (XRD). It was shown from the XRD results that a higher ball to powder weight ratio (BPR) is advantageous in preparing amorphous alloys powder. The microstructure and shape of the powder was observed by scanning electron microscope (SEM). It was shown from the SEM results that the as-milled amorphous alloys powder is flake shape and assembles together to be agglomeration structure, which is a typical morphology of amorphous powders prepared by MA. Thermodynamic properties and crystallization kinetics behavior of the as-milled amorphous alloys powder were measured by differential scanning calorimeter (DSC). The supercooled liquid region △Tx is broad (up to 119K) and the reduction glass transforming temperature Trg (0.78) is great, which shows that the as-milled amorphous alloys powder has a strong glass-forming ability and the thermal stability of the powder is excellent.
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Authors: Petr Urban, Francisco Gomez Cuevas, Juan M. Montes, Jesus Cintas
Abstract: The amorphization process by mechanical alloying in the Fe-Si alloy system has been studied. High energy ball milling has been applied for alloys synthesis. X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to monitor the structural and phase transformations through the different stages of milling. The addition of amorphous boron in the milling process and the increase of the milling time were used to improve the formation of the amorphous phase. Heating the samples resulted in the crystallization of the synthesized amorphous alloys and the appearance of equilibrium intermetallic compounds.
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Authors: Y.B. Yuan, Rui Xiao Zheng, Su Jing Ge, Han Yang, Chao Li Ma
Abstract: Al86Ni7Y4.5Co1La1.5 (at.%) alloy powder was produced by argon gas atomization process. After high-energy ball milling, the powder was consolidated and extruded by using vacuum hot press sintering under different process conditions, sintering temperature, extrusion pressure, sintering time, etc.. The microstructure and morphology of the powder and consolidated bulk alloy were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The phase transformation of the powder was investigated by differential scanning calorimetry (DSC). Mechanical properties of the consolidated bulk alloy were examined. The results showed that as the milling time increase, the volume fraction of amorphous materials and the hardness and yield strength of the bulk alloy were obvious improved.
281
Authors: F.L. Catto, A.H.G. Gabriel, C. Bolfarini, Claudio Shyinti Kiminami, Conrado Ramos Moreira Afonso
Abstract: Glassy overspray powders of Ni59Nb35Sn6 (at%) bulk metallic glass (BMG) obtained by spray forming were used in order to produce coatings on AISI 1020 mild steel substrate by laser cladding of the pre-placed powders. Different laser parameters, resulting in a variation of the power density, PD (J/mm2), were tested with a Yb fiber laser (up to 500 W). Gas atomized powders, suction cast sample trough copper mold casting and the laser clad tracks were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and coatings were subjected to measurements of Vickers microhardness. Atomized powder obtained showed no crystalline phases formation up to 425 μm, indicating good glass forming ability (GFA) of Ni59Nb35Sn6 (at%) alloy. Microstructure characterization confirmed maximum glassy dimension of tc =1mm for the Ni59Nb35Sn6 (at%). Laser cladding track showed nanocrystalline phases embedded in a glassy matrix with Vickers microhardness ranging from 336 to 1184 HV.
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