ABSTRACT New techniques for manufacturing of biomaterials using additive/substrate manufacturing such as melting laser sintering (SLM) or CAD/CAM milling use micrometric metal powders to build custom parts. CoCrMo alloys are commonly used as biomaterials due to biocompatibility, high corrosion resistance and good mechanical properties. In this work, Cr-Co-based powder was obtained by mechanical alloying of Cr-Co-Mo-W alloy, using different Ball/Powder-Ratios (BPR) and thermal treatments. The powders were deagglomerated and characterized by X-ray diffraction (XRD) and Scanning electron microscopy (SEM). Based on SEM micrographs, the particle size analysis was used to compare the particles spheroidizing degree, using Feret’s diameter. The XRD patterns shown Co(solid-solution) as crystalline phase. The results of particles size indicates a decrease of Feret’s diameter in BPR (Ball/Powder-Ratio) from 4:1 to 6:1 understanding that from this ratio there is no significant decrease of this relation but there is an average size increase with losses in morphological aspect. The comparison between atomized powders and powder developed in this work indicates that atomized products present relation close to one which indicates there is uniformity in the particles spherical shape. Comparing ground powders from 6:1 ratio (before and after thermal treatment) there is a considerable decrease of Feret’s diameter being it decreased from 1.75 to 1.4, an increase of about 46% in particles spheroidizing.

Abstract In this work, CoCrMo-base alloys specimens were produced by additive manufacturing using selective laser melting (SLM) as well as CAD/CAM milling. For SLM specimens, spherical particles were laser processed at 1320°C under argon atmosphere and submitted to thermal stress relieving at 750°C–45min. Specimens from CoCrMo blocks were milled by CAD/CAM machining and sintered at 1300°C–60min. The materials from both techniques were characterized by relative density, dilatometry, SEM/BSE, OM and XRD analysis. The mechanical properties were determined by Vickers hardness and tensile tests. The specimens from both techniques exhibited single phase γCo (FCC) and CTE of 14 x10-6 °C-1. Relative density of 95.4%/ 85.6%, hardness values near 400HV/ 350HV and UTS of 905MPa/ 780MPa were measured for SLM and CAD/CAM specimens, respectively. Higher relative density is the main factor for increased mechanical properties of SLM specimens. On the other hand, both SLM and CAD/CAM specimens present properties in accordance with ISO-22674 recommendations, compatible with dental applications such as bridges containing four or more elements as well as fully dense pontics.

The microstructural alterations suffered during the process of drawing deformation and subsequent annealing of pearlitic steel wires, were evaluated by scanning electron microscopy and atomic force microscopy. The deformed material showed the curling structure in cross section while, in the longitudinal section, the lamellae was aligned with the drawing direction. The microstructural characterization of deformed samples also allowed observing an interlamellar spacing reduction and the intermediate lamellae alignment process. After the heat treatment at 1000ºC for 5 min the microstructure was restored, however, few recrystallized grains were observed. The recovery was the dominant phenomenon, due to factors associated with curling structure that inhibited recrystallization.

In this work the theoretical solutions based upon the upper-bound theorem recently proposed by Pérez and Luri [Mech. Mater. 40 (2008) 617] for the equal channel angular extrusion process (ECAE) are analyzed by performing a 25 central composite factorial analysis. The uniaxial mechanical properties of commercial pure aluminium are considered by assuming isotropic nonlinear work-hardening combined to von Mises and Drucker isotropic yield criteria to predict the ECAE load and the effective plastic strain. From the proposed 25 factorial analysis, the main parameters affecting the ECAE pressure may be ranked as: (1) Friction factor, (2) die channels intersection angle, (3) outer and (4) inner die corners fillet radii and lastly, (5) plunger velocity. Alternatively, the effective plastic strain is mainly controlled by the die channels intersection angle and, in a less extent, by the outer and inner die corners fillet radii.

O presente trabalho reporta os resultados da caracterização microestrutural realizada em bandas de cisalhamento adiabáticas induzidas num aço IF estabilizado ao titânio, visando a avaliar a formação e o crescimento de danos. O material foi deformado via compressão dinâmica sob altas taxas de deformação (> 5,0×10(4) s-1) numa barra de impacto de Hopkinson a -196ºC. A observação detalhada das regiões de cisalhamento e das superfícies de fratura foi realizada via microscopia eletrônica de varredura (MEV). A recristalização dinâmica no interior das bandas de cisalhamento adiabáticas foi o evento precursor, que permitiu um caminho para a propagação das fissuras. Pode-se concluir que a fratura do material foi o resultado de um processo de clivagem dirigido por maclas de deformação e bandas de deslizamento.

The present work reports the results of microstructural characterization performed in adiabatic shear bands forced in titanium-stabilized IF steel to evaluate damage formation and growth. Dynamic compression tests were done at -196ºC under large strain rates (> 5.0×104 s-1) with the aid of a Split Hopkinson Bar. Scanning electron microscopy (SEM) was employed to investigate the shear regions and the fracture surfaces in detail. The dynamic recrystallization within ASB was the precursor event and provided a path for crack propagation. It can be concluded that the failure of the material was the result of the cleavage process driven by the presence of deformation twins and slip bands.

O presente trabalho visa a investigar o efeito da deformação plástica severa introduzida pelo processo de embutimentos sucessivos, seguidos de forjamento rotativo, trefilação e do subseqüente recozimento a 950°C por 1 hora na microtextura de um compósito nanoestruturado de Nb-30%Cu em volume. A caracterização microestrutural foi realizada com o auxílio das técnicas de microscopia ótica (MO), microscopia eletrônica de varredura (MEV) e difração de elétrons retroespalhados (EBSD). Após o recozimento, a matriz de cobre exibia uma microestrutura totalmente recristalizada com uma textura do tipo fibra-gama. Os filamentos de Nb, após o processamento termomecânico empregado, exibiram uma fraca textura do tipo fibra-alfa. Os resultados mostraram que ocorreu um processo de recristalização parcial em várias áreas dos filamentos de Nb, em virtude de uma competição microestrutural.

The effect of severe plastic deformation introduced by the bundling-and-drawing process and the subsequent annealing in vacuum at 950°C for 1 hour on the microtexture of Nb-30%Cu (in vol%) nanostructured composite has been investigated. The microstructural characterization was carried out using light optical microscopy (LOM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The microstructure of the Cu matrix was completely recrystallized, displaying a gamma-fiber texture after annealing. A weak alpha-fiber texture arises in the Nb filaments after the employed thermomechanical process. Results showed that in several areas of the multifilamentary niobium, a partial recrystallization developed, indicating microstructural competition.