Navegando por Autor "Bolfarini, Claudemiro"
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Artigo Consolidation of the Cu46Zr42Al7 Y5 amorphous ribbons and powder alloy by hot extrusion(FapUNIFESP (SciELO), 2012-08-09) Peres, Maurício Mirdhaui; Mellea, Ana Karla; Bolfarini, Claudemiro; Botta, Walter José; Jorge Jr., Alberto Moreira; Kiminami, Claudio ShyintiThe amorphous Cu46Zr42Al7Y5 alloy presents large supercooled liquid region (∆TX = 100 K), with a viscosity of about 106 N.s/m2 where the material can flow as a liquid, making it possible an easy deformation in this temperature region. The aim of this work was to analyze processing routes to produce bulks of metallic glasses. Two kinds of materials were used: amorphous powders and ribbons, both were consolidated by hot extrusion in temperatures inside the range between Tg and Tx, with a ram speed of 1 mm/min and extrusion ratio of 3 : 1. Analysis of X-Ray Diffratometry (XRD), Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM), revealed that the proposed consolidation routes were effective to produce large bulks of amorphous materials, even with the strong decreasing of ∆TX observed after deformation by milling and during extrusionArtigo Nanoquasicrystalline Al–Fe–Cr–Nb alloys produced by powder metallurgy(Elsevier, 2013-11-15) Peres, Maurício Mirdhaui; Audebert, Fernando E.; Galano, Marina L.; Rios, C. Triveño; Kasama, H.; Kiminami, Claudio Shyinti; Botta, Walter Jose; Bolfarini, ClaudemiroNano-quasicrystalline Al–Fe–Cr based alloys produced by rapid solidification processes exhibit high strength at elevated temperatures. Nevertheless, the quasicrystalline particles in these systems become unstable at high temperature limiting the industrial applications. In early works, it was observed that the use of Nb or Ta increases the stability of the Al–Fe–Cr quasicrystalline phase delaying the microstructural transformation to higher temperatures. Thus, these nano-quasicrystalline Al-based alloys have become promising new high strength material to be used at elevated temperatures in the automotive and aero-nautical industries. In previous works, nano-quasicrystalline Al–Fe–Cr–Nb based alloys were obtained by rapid solidification using the melt-spinning technique. In order to obtain bulk alloys for industrial applications other fabrication routes such as powder production by gas atomization followed by compaction and extrusion are required. In the present work, the production of Al–Fe–Cr–Nb based alloys by powder atomization at laboratory scale was investigated. The powders obtained were sieved in different ranges of sizes and the microstructures were characterised by means of X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive of X-ray analysis. Mechanical properties have been measured by compression tests at room temperature and at 250 C. It was observed that a very high temperature is required to produce these alloys by gas atomization; the icosahedral quasicrystalline phase can be retained after the atomization in powder sizes typically under 75 lm, and also after the extrusion at 375 C. The extruded bars were able to retain a very high strength at elevated temperature, around 60% of the yield stress at room temperature, in contrast with the 10–30% typically obtained for many commercial Al alloys