Formation of a quasicrystalline phase in Al–Mn base alloys cast at intermediate cooling rates

Al-rich 94Al–6Mn and 94Al–4Mn–2Fe alloys were suction-cast to evaluate thefeasibility of obtaining bulk quasicrystal-strengthened Al-alloys at intermediatecooling rates alloyed with non-toxic, easily accessible and affordable additions.The influence of different cooling rates on the potential formation of a quasicrystallinephase was examined by means of scanning and transmissionelectron microscopy, X-ray diffraction and differential scanning calorimetry.Increased cooling rates in the thinnest castings entailed a change in samplephase composition. The highest cooling rates turned out to be insufficient toform an icosahedral quasicrystalline phase (I-phase) in the binary alloy. Instead,an orthorhombic approximant phase occurred (L-phase). The addition of Fe tothe 94Al–6Mn binary alloy enhanced the formation of a quasicrystalline phase.At intermediate cooling rates of 102–103 K/s, various metastable phases wereformed, including decagonal and icosahedral quasicrystals and their approximants.Rods (1 mm in diameter) composed of I-phase particles embedded in Almatrix exhibited a hardness of 1.5 GPa, much higher than the 1.1 GPa of 94Al–6Mn

Enhancement of Mechanical Properties of Aluminum and 2124 Aluminum Alloy by the Addition of Quasicrystalline Phases

A structural and mechanical characterization of pure aluminum and 2124 T6 aluminum alloy reinforced with quasicrystalline phases of composition Al65Cu20Fe15 and Al70.5Pd21Mn8.5 (%at.) were performed. The quasicrystalline phases were synthesized by arc melting and then milled to produce powder of the alloys, which were then mechanical mixed with the starting powders of aluminum and 2124 aluminum alloy. The composites were produced by hot extrusion of a mechanical mixture containing 20% (%wt.) of the reinforcing phases on the metallic matrix. The structural characterization of the composites was carried out by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Mechanical characterization was carried out by Vickers hardness measurements and torsion tests at room temperature. The pure aluminum/quasicrystal composite showed the presence of the same phases from the starting powder mixture while for the 2124 aluminum alloy/Al65Cu20Fe15 the quasicrystalline phase transformed to the tetragonal ω-Al7Cu2Fe during the solution heat treatment. Mechanical strength of the composites presented a substantial increase in comparison to the original matrix metal. While the equivalent ultimate tensile strength of the Al/quasicrystal composites reached values up to 215MPa and Vickers hardness up to 60HV, the 2124/quasicrystal composites reached values up to 670MPa and Vickers hardness up to 190HV

Práticas baseadas em evidências publicadas no Brasil: identificação e análise de suas vertentes e abordagens metodológicas

Revisão integrativa de estudos brasileiros sobre práticas baseadas em evidências (PBE) em saúde, publicados em periódicos ISI/JCR, nos últimos 10 anos. O objetivo foi identificar as especialidades que mais realizaram estes estudos, seus enfoques e abordagens metodológicas. A partir de critérios de inclusão, foram selecionados 144 trabalhos. Os resultados indicam que a maior quantidade de estudos feitos em PBE foram sobre infância e adolescência, infectologia, psiquiatria/saúde mental e cirurgia. Os enfoques predominantes foram prevenção, tratamento/reabilitação, diagnóstico e avaliação. As metodologias mais empregadas foram revisão sistemática sem ou com metanálise, revisão de protocolos ou síntese de estudos de evidências já disponíveis, e revisão integrativa. Constata-se forte expansão multiprofissional da PBE no Brasil, contribuindo para a busca de práticas mais criteriosas pela reunião, reconhecimento e análise crítica dos conhecimentos produzidos. O estudo contribui também para a própria análise dos modos de fazer pesquisa e novas possibilidades de investigação