16 resultados para SMAT


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Titanium and its alloys are excellent candidates for biomedical implant. However, they exhibit relatively poor tribological properties. In this study, a two-step treatment including surface mechanical attrition treatment (SMAT) combined with thermal oxidation process has been developed to improve the tribological properties and biocompatibility of Ti. Ti after two-step treatment shows excellent wear-resistance and biocompatibility among all Ti samples, which can be ascribed to the highest surface energy, well crystallinity of rutile layer on its surface. Overall, the two-step treatment is a prospective method to produce excellent biomedical Ti materials.

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Nanostructured metals are a promising class of biomaterials for application in orthopedics to improve the mechanical performance and biological response for increasing the life of biomedical implants. Surface mechanical attrition treatment (SMAT) is an efficient way of engineering nanocrystalline surfaces on metal substrates. In this work, 316L stainless steel (SS), a widely used orthopedic biomaterial, was subjected to SMAT to generate a nanocrystalline surface. Surface nanocrystallization modified the nature of the oxide layer present on the surface. It increased the corrosion-fatigue strength in saline by 50%. This increase in strength is attributed to a thicker oxide layer, residual compressive stresses, high strength of the surface layer, and lower propensity for intergranular corrosion in the nanocrystalline layer. Nanocrystallization also enhanced osteoblast attachment and proliferation. Intriguingly, wettability and surface roughness, the key parameters widely acknowledged for controlling the cellular response remained unchanged after nanocrystallization. The observed cellular behavior is explained in terms of the changes in electronic properties of the semiconducting passive oxide film present on the surface of 316L SS. Nanocrystallization increased the charge carrier density of the n-type oxide film likely preventing denaturation of the adsorbed cell-adhesive proteins such as fibronectin. In addition, a net positive charge developed on the otherwise neutral oxide layer, which is known to facilitate cellular adhesion. The role of changes in the electronic properties of the oxide films on metal substrates is thus highlighted in this work. This study demonstrates the advantages of nanocrystalline surface modification by SMAT for processing metallic biomaterials used in orthopedic implants.

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利用表面机械研磨处理(SMAT)技术在Zr片状拉伸样品表面施加剧烈变形,获得超细/纳米晶粒组织的变形细化表层,其中Zr板厚度1 mm,两侧变形层厚度均为100μm.拉伸实验结果表明,表层细化组织提高了屈服强度和抗拉强度,使加工硬化能力及伸长率下降.应变速率在10~(-4)~10~(-3)s~(-1)范围时,拉伸强度随应变速率的提高而提高;应变速率增大至10~(-2)s~(-1)量级时,抗拉强度下降.扫描电镜观察显示出韧性韧窝状断裂特征.

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The surface mechanical attrition treatment (SMAT) technique was developed to synthesize a nanocrystalline (NC) layer on the surface of metallic materials for upgrading their overall properties and performance. In this paper, by means of SMAT to a pure zirconium plate at the room temperature, repetitive multidirectional peening of steel shots (composition (wt%): 1C, 1.5Cr, base Fe) severely deformed the surface layer. A NC surface layer consisting of the intermetallic compound FeCr was fabricated on the surface of the zirconium. The microstructure characterization of the surface layer was performed by using X-ray diffraction analysis, optical microscopy, scanning and transmission electron microscopy observations. The NC surface layer was about 25 mu m thick and consisted of the intermetallic compound FeCr with an average grain size of 25 +/- 10 nm. The deformation-induced fast diffusion of Fe and Cr from the steel shots into Zr occurred during SMAT, leading to the formation of intermetallic compound. In addition, the NC surface layer exhibited an ultrahigh nanohardness of 10.2 GPa.

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Se realizan dos investigaciones empíricas. El objetivo de la primera consiste en comprobar el efecto de la aplicación de un programa diseñado para mejorar el empleo de estrategias metacognitivas en el aprendizaje de chicos y chicas. En la segunda, el objetivo es comprobar qué grupos del sistema educativo tiene un mayor dominio de las estrategias de aprendizaje. La muestra del primer experimento la conforman 177 adolescentes de dos centros públicos de la Comunidad de Madrid. La muestra del segundo experimento son estudiantes de la Facultad de Educación de la Universidad Complutense de Madrid durante 1996-1997, alumnos de 3õ y 4õ de ESO y alumnos de 3õ de BUP, en total 472. En el primer estudio, se seleccionan tres tipos de variables: la inteligencia general, la motivación hacia el estudio y las estrategias cognitivas y metacognitivas de aprendizaje. Se pretende observar el posible efecto diferencial que ejerce el programa en función de pertenecer a la LOGSE o al anterior sistema educativo. Para satisfacer dicho objetivo se plantea un diseño clásico con medidas en el pre y postest, estableciendo un grupo experimental y otro de control. Las variables independientes son el tratamiento, el sexo y el sistema educativo. El segundo estudio pretende determinar si existe una utilización diferencial de las estrategias de aprendizaje entre estos tres grupos, se identifican aquellos en que difieren y en cuáles no, de modo que aporte una información útil para dirigir futuros programas de intervención sobre estrategias de aprendizaje. Los instrumentos de medida para el primer experimento son las pruebas TIG-2 (Test de Intelegencia General), SMAT (Test de motivación en adolescentes) y ACRA (Escalas de Estrategias de aprendizaje). El segundo experimento utiliza el LASSI (Learning and Study Strategies Inventory) y ACRA. El primer estudio es un diseño cuasi experimental pretest-postest con grupo de control. El segundo, utiliza un análisis de varianza con variable categórica del grupo educativo como factor intersujetos y como factores intrasujetos, las escalas que componen los instrumentos de LASSI y las de ACRA. También se emplea el test de Scheffe para comprobar entre qué grupos de variable independiente se producen las diferencias estadísticas y en qué dirección. Los resultados del primer experimento indican que la participación en el programa no produce diferencias significativas en las estrategias de aprendizaje, el nivel de inteligencia general y la motivación. En cuanto a las hipótesis relacionadas con el sexo, se observa que tras la intervención existen diferencias significativas entre las medias de estrategias de aprendizaje, nivel de inteligencia general y las variables motivacionales. Respecto al efecto del sistema educativo después de la intervención, concluye que no existen diferencias al respecto en cuanto a estrategias de aprendizaje, funciones intelectivas y rasgos motivacionales. No obstante, en el análisis univariante se aprecian diferencias significativas debidas al sistema educativo, en las estrategias de recuperación, en el nivel de inteligencia general y en la asertividad. En cuanto a los efectos intereactivos entre las variables independientes, tras la intervención no se encuentran diferencias significativas en el conjunto de las variables dependientes debidas a la interacción entre el sexo y el Sistema Educativo.Tampoco resultaron significaticas las diferencias entre las medidas del conjunto de variables dependientes, debidas a la interacción entre la participación en el programa y el Sistema Educativo. Respecto al efecto de la interacción entre la participación en el Programa y el Sexo, se concluye que no hay diferencias significativas entre las medias de las estrategias de aprendizaje, el nivel de inteligencia general y la motivación debidas a dicha interacción. Los resultados del segundo estudio confirman parcialmente que los estudiantes universitarios muestran un mayor rendimiento en casi todas las estrategias analizadas. En cuanto a los resultados con la prueba ACRA, los universitarios muestran puntuaciones superiores a los otros dos grupos. Parece que los estudiantes al acceder a niveles superiores dentro del sistema educativo, deben adquirir nuevas herramientas de trabajo que les permitan tener éxito en sus estudios. Es previsible que los alumnos de ESO frente a los de BUP consigan un mayor dominio de los contenidos procedimentales y, por ende, de las estrategias de aprendizaje, a medida que se vayan consolidando sus principios psicopedagógicos en la comunidad educativa.

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In present study, the formation of bioactive anatase on bulk titanium (Ti) by hybrid surface mechanical attrition treatment (SMAT) is reported. A commercial pure Ti plate first underwent SMAT in a vacuum for 1 h to produce a nanocrystalline layer with a thickness of about 30 µm, and then the nanocrystalline Ti (30 nm) was transformed into mesoporous anatase with a grain size 10 nm by chemical oxidation and calcination. The mesoporous anatase showed excellent bioactivity while being soaked in simulated body fluid, which could be attributed to the unique nanostructure on the SMAT Ti surface.

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In this work, the interaction between hydrogen peroxide (H2O2) and a gradient structured Ti was investigated extensively. The gradient structured Ti (SMAT Ti) was produced by surface mechanical attrition treatment (SMAT), and then it was immersed in H2O2 solution for different time until 48 h at room temperature (25 °C). The structure and surface morphology evolution were examined by Raman spectra and scanning electron microscopy (SEM). The formation mechanism of nanoporous titania was discussed based on above results.

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Surface mechanical attrition treatment (SMAT), a novel surface severe plastic deformation method, was carried out for titanium (Ti) to create a gradient-structured Ti (SMAT Ti). The tribological behaviour was studied under different loads and dry sliding conditions. The results showed that the deformation layer of SMAT Ti was about 160 μm. The friction and wear results showed that the wear resistance of SMAT Ti was enhanced compared to the coarse-grained (CG) counterpart. SMAT Ti showed abrasive wear under 1 and 5 N, and exhibited abrasive and adhesive wear under 2 N. While CG Ti showed abrasive and adhesive wear under 1-2 N, and exhibited abrasive wear under 5 N for the work hardening effects.

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A nanocrystalline (NC) layer with the thickness of 30 µm was produced on pure titanium surface by surface mechanical attrition treatment (SMAT). Microstructure observation indicated that the grain size increases with depth from the treated surface. The friction coefficient decreases and the wear resistance increases with the SMAT sample as compared to its coarse-grained counterpart. The improvement of the wear properties could be attributed to the higher hardness of SMAT sample.

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Surface mechanical attrition treatment (SMAT), a novel surface severe plastic deformation method, was carried out for titanium (Ti) to create a gradient-structured Ti (SMAT Ti). The tribological behaviour was studied under different loads and dry sliding conditions. The results showed that the deformation layer of SMAT Ti was about 160 lm. The friction and wear results showed that the wear resistance of SMAT Ti was enhanced compared to the coarse-grained (CG) counterpart. SMAT Ti showed abrasive wear under 1 and 5 N, and exhibited abrasive and adhesive wear under 2 N. While CG Ti showed abrasive and adhesive wear under 1–2 N, and exhibited abrasive wear under 5 N for the work hardening effects.

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Surface mechanical attrition treatment (SMAT) is a mechanical peening process used to generate ultrafine grain surfaces on a metal. SMAT was carried out on pure magnesium using different attrition media (zirconia [ZiO2], alumina [Al2O3], and steel balls) to observe the effect on microstructure, surface residual stress, surface composition, and corrosion. Surface contamination from SMAT was characterized using glow discharge optical emission spectroscopy (GDOES). The SMAT process produced a refined grain structure on the surface of Mg but resulted in a region of elemental contamination extending ~10 μm into the substrate, regardless of the media used. Consequently, SMAT-treated surfaces showed an increased corrosion rate compared to untreated Mg, primarily through increased cathodic kinetics. This study highlights the issue of contamination resulting from the SMAT process, which is a penalty that accompanies the significant grain refinement of the surface produced by SMAT. This must be considered if attempting to exploit grain refinement for improving corrosion resistance.

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The contact load-bearing response and surface damage resistance of multilayered hierarchical structured (MHSed) titanium were determined and compared to monolithic nanostructured titanium. The MHS structure was formed by combining cryorolling with a subsequent Surface Mechanical Attrition Treatment (SMAT) producing a surface structure consisted of an outer amorphous layer containing nanocrystals, an inner nanostructured layer and finally an ultra-fine grained core. The combination of a hard outer layer, a gradual transition layer and a compliant core results in reduced indentation depth, but a deeper and more diffuse sub-surface plastic deformation zone, compared to the monolithic nanostructured Ti. The redistribution of surface loading between the successive layers in the MHS Ti resulted in the suppression of cracking, whereas the monolithic nanograined (NG) Ti exhibited sub-surface cracks at the boundary of the plastic strain field. Finite element models with discrete layers and mechanically graded layersrepresenting the MHS system confirmed the absence of cracking and revealed a 38% decrease in shear stress in the sub-surface plastic strain field, compared to the monolithic NG Ti. Further, the mechanical gradation achieves a more gradual stress distribution which mitigates the interface failure and increases the interfacial toughness, thus providing strong resistance to loading damage. © 2014 Elsevier Ltd.