Microstructural Characterization of a Laser Surface Remelted Cu-Based Shape Memory Alloy

Cu-based shape memory alloys (SMAs) present some advantages as higher transformation temperatures, lower costs and are easier to process than traditional Ti-based SMAs but they also show some disadvantages as low ductility and higher tendency for intergranular cracking. Several studies have sought for a way to improve the mechanical properties of these alloys and microstructural refinement has been frequently used. It can be obtained by laser remelting treatments. The aim of the present work was to investigate the influence of the laser surface remelting on the microstructure of a Cu-11.85Al-3.2Ni-3Mn (wt%) SMA. Plates were remelted using three different laser scanning speeds, i.e. 100, 300 and 500 mm/s. The remelted regions showed a T-shape morphology with a mean thickness of 52, 29 and 23 µm and an average grain size of 30, 29 and 23µm for plates remelted using scanning speed of 100, 300 and 500 mm/s, respectively. In the plates remelted with 100 and 300 mm/s some pores were found at the root of the keyhole due to the keyhole instability. We find that the instability of keyholes becomes more pronounced for lower scanning speeds. It was not observed any preferential orientation introduced by the laser treatment

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 w-Al7Cu2 Fe 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.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fed Univ Sao Carlos UFSCAR, Grad Program Mat Sci & Engn, Rod Washington Luiz,Km 235, BR-13565905 Sao Carlos, SP, BrazilState Univ Rio de Janeiro UERJ, Polytech Inst, R Bonfim 25, BR-28625570 Nova Friburgo, RJ, BrazilFed Univ Sao Paulo UNIFESP, Sci & Technol Inst, R Talim 330, BR-12231280 Sao Jose Dos Campos, SP, BrazilFed Univ Sao Carlos UFSCAR, Dept Mat Engn, Rod Washington Luiz,Km 235, BR-13565905 Sao Carlos, SP, BrazilScience and Technology Institute, Universidade Federal de São Paulo (UNIFESP), R. Talim 330, 12231-280, São José dos Campos, SP, BrazilFAPESP: 2011/06497-9Web of Scienc

Analysis of physico-chemical characteristics of two surface treatments in dental mini-implants

Objetivos: A otimização das superfícies de titânio é essencial para acelerar o processo de osseointegração e viabilizar tratamentos reabilitadores em um curto período de tempo. O objetivo deste estudo foi avaliar comparativamente dois tratamentos de superfície do tipo nanométrico em mini-implantes dentários, sendo um comercial e outro experimental, quanto à caracterização morfológica e química. Materiais e métodos: Dois grupos foram avaliados: G1 – mini-implan­tes de titânio com tratamento de superfície Ossean® (Intra-Lock); e G2 – mini-implantes de titânio com tratamento de superfície experimental. Após o tratamento experimental, por meio de ataque com ácido fosfórico seguido de tratamen­to alcalino, os implantes foram avaliados por microscopia eletrônica de varredura (MEV), em dois modos diferentes: SE (elétron secundário), que analisa as alterações topográficas nas amostras, e BSE (elétron retroespalhado), que analisa as alterações ou flutuações de composição na superfície da amostra. A composição química foi verificada por um sistema de espectroscopia de energia dispersiva de raios X (EDS). Resultados: As imagens de MEV confirmaram diferenças nas superfícies G1 e G2, com presença de poros nanométricos no G2, enquanto a análise de EDS demonstrou a incorporação de elementos característicos da estimulação da neoformação óssea. Conclusões: O tratamento de superfície experimen­tal, por ser um processo químico, além de simples, foi eficaz na formação de uma superfície rugosa e com capacidade bioativa. DESCRITORES | Implantes dentais; Microscopia eletrônica de varredura; Osseointegração.Objectives: The optimiza­tion of titanium surfaces is essential to accelerate the process of osseointegration and to enable rehabilitative treatments in a short period of time. The objective of the present study was to evaluate comparatively two surface treatments of the nanometric type in dental mini-implants, being a commercial and another experimental, regarding the morphological and chemical characterization. Material and methods: Two groups were evaluated: G1 – titanium mini-implants with surface treatment Ossean® (Intra-Lock) and G2 – titanium mini-implants with experimental surface treatment. After the experimental treatment, by means of an attack with phosphoric acid followed by alkaline treatment, the implants were evaluated by scanning electron microscopy (SEM), in two different ways, SE (secondary electron) that analyzes the topographic changes in the samples and BSE (back-scattered electrons) that analyzes the composition changes or fluctuations in the sample surface. The chemical composition was analyzed by an X-ray dispersive energy spectroscopy (EDX) system. Results: SEM images confirmed differences in G1 and G2 surfaces, with the presence of nanometric pores in G2, whereas EDX analysis demonstrated the incorporation of elements characteristic of the stimulation of bone neoformation. Conclusions: The experimental surface treatment, as a chemical process, besides being simple, was effective in the formation of a rough surface and with bioactive capacity. DESCRIPTORS | Dental implants; Scanning electron microscopy; Osseointegration

Phase formation, thermal stability and mechanical properties of a Cu-Al-Ni-Mn shape memory alloy prepared by selective laser melting

Selective laser melting (SLM) is an additive manufacturing process used to produce parts with complex geometries layer by layer. This rapid solidification method allows fabricating samples in a non-equilibrium state and with refined microstructure. In this work, this method is used to fabricate 3 mm diameter rods of a Cu-based shape memory alloy. The phase formation, thermal stability and mechanical properties were investigated and correlated. Samples with a relative density higher than 92% and without cracks were obtained. A single monoclinic martensitic phase was formed with average grain size ranging between 28 to 36 μm. The samples exhibit a reverse martensitic transformation temperature around 106 ± 2 °C and a large plasticity in compression (around 15±1%) with a typical “double-yielding” behaviour

Phase Formation, Thermal Stability and Mechanical Properties of a Cu-Al-Ni-Mn Shape Memory Alloy Prepared by Selective Laser Melting

Selective laser melting (SLM) is an additive manufacturing process used to produce parts with complex geometries layer by layer. This rapid solidification method allows fabricating samples in a non-equilibrium state and with refined microstructure. In this work, this method is used to fabricate 3 mm diameter rods of a Cu-based shape memory alloy. The phase formation, thermal stability and mechanical properties were investigated and correlated. Samples with a relative density higher than 92% and without cracks were obtained. A single monoclinic martensitic phase was formed with average grain size ranging between 28 to 36 μm. The samples exhibit a reverse martensitic transformation temperature around 106 ± 2 °C and a large plasticity in compression (around 15±1%) with a typical “double-yielding” behaviour