Improvement of the biomedical properties of titanium using SMAT and thermal oxidation

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.

Nanocrystalline titanium to mesoporous anatase with high bioactivity

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.

The biomedical application of Ti after severe plastic deformation and thermal oxidation, especially the friction and wear properties of Ti

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.

Improved contact load-bearing capacity of ultra-fine grained titanium : Multilayering and grading

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.

Grain Refinement at the Nanoscale Via Mechanical Twinning and Dislocation Interaction in a Nickel-Based Alloy

A nanostructured surface layer was formed on an Inconel 600 plate by subjecting it to surface mechanical attrition treatment at room temperature. Transmission electron microscopy and high-resolution transmission electron microscopy of the treated surface layer were carried out to reveal the underlying grain refinement mechanism. Experimental observations showed that the strain-induced nanocrystallization in the current sample occurred via formation of mechanical microtwins and subsequent interaction of the microtwins with dislocations in the surface layer. The development of high-density dislocation arrays inside the twin-matrix lamellae provides precursors for grain boundaries that subdivide the nanometer-thick lamellae into equiaxed, nanometer-sized grains with random orientations.

Effect of grain size on corrosion of high purity aluminium

A complete understanding of how grain refinement, grain size, and processing affect the corrosion resistance of different alloys has not yet been fully developed. Determining a definitive 'grain size-corrosion resistance' relationship, if one exists, is inherently complex as the processing needed to achieve grain refinement also imparts other changes to the microstructure (such as texture, internal stress, and impurity segregation). This work evaluates how variation in grain size and processing impact the corrosion resistance of high purity aluminium. Aluminium samples with a range of grain sizes, from ∼100 μm to ∼2000 μm, were produced using different processing routes, including cold rolling, cryo rolling, equal channel angular pressing, and surface mechanical attrition treatment. Evaluation of all the samples studied revealed a tendency for corrosion rate to decrease as grain size decreases. This suggests that a Hall-Petch type relationship may exist for corrosion rate and grain size. This phenomenon, discussed in the context of grain refinement and processing, reveals several interesting and fundamental relationships.

In Situ Synthesis Of Nanocrystalline Intermetallic Layer During Surface Plastic Deformation Of Zirconium

By means of a surface plastic deformation method a nanocrystalline (NC) intermetallic compound was in situ synthesized on the surface layer of bulk zirconium (Zr). Hardened steel shots (composition: 1.0C, 1.5Cr, base Fe in wt.%) were used to conduct repetitive and multidirectional peening on the surface layer of Zr. The microstructure evolution of the surface layer was investigated by X-ray diffraction and scanning and transmission electron microscopy observations. The NC intermetallic layer of about 25 gm thick was observed and confirmed by concentration profiles of Zr, Fe and Cr, and was found to consist of the Fe100-xCrx compound with an average grain size of 22 nm. The NC surface layer exhibited an extremely high average hardness of 10.2 GPa. The Zr base immediately next to the compound/Zr interface has a grain size of similar to 250 nm, and a hardness of similar to 3.4 GPa. The Fe100-xCrx layer was found to securely adhere to the Zr base. (c) 2007 Elsevier B.V All rights reserved.

The main factor influencing the tensile properties of surface nano-crystallized graded materials

The improved mechanical properties of surface nano-crystallized graded materials produced by surface severe plastic deformation ((SPD)-P-2) are generally owing to the effects of the refined structure, work-hardened region and compressive residual stress. However, during the (SPD)-P-2 process, residual stress is produced simultaneously with work-hardened region, the individual contribution of these two factors to the improved mechanical properties remains unclear. Numerical simulations are carried out in order to answer this question. It is found that work hardening predominates in improving the yield strength and the ultimate tensile strength of the surface nano-crystallized graded materials, while the influence of the residual stress mainly emerges at the initial stage of deformation and decreases the apparent elastic modulus of the surface nano-crystallized graded materials, which agrees well with the experimental results. (C) 2010 Elsevier B.V. All rights reserved.

Particle dynamics and heat transfer at workpiece surface in heat treatment fluidised beds

The particle behaviour is studied by the analysis of particle images taken with a high speed CCD digital video camera. The comparison of particle dynamics is performed for the fluidised beds without part, with single part and with multi-parts. The results show that there are significant differences in particle behaviours both in different beds and at different locations at part surfaces. The total and radiative heat transfer coefficients at different surfaces of a metallic component in a high temperature fluidised bed are measured by a heat transfer probe developed in the present work. The principle of the heat transfer probe is to measure the change in temperature of the heated metallic piece with time and, then, to extract the heat flux and heat transfer coefficients. The structure of the probe is optimized with numerical simulation of energy conservation for measuring the heat transfer coefficient of 150~600 W/m2 K. The relationship between the particle dynamics and the heat transfer is analysed to form the basis for future more rational designs of fluidised beds as well as for improved quality control.

Particle dynamics and heat transfer at workpiece surface in heat treatment fluidised beds

The particle behaviour in a heat treatment fluidised bed was studied by the analysis of particle images taken with a high speed CCD digital video camera. The comparison of particle dynamics was performed for the fluidised beds without part, with single part and with multi-parts. The results show that there are significant differences in particle behaviours both in different beds and at different locations of part surfaces. The total and radiative heat transfer coefficients at different surfaces of a metallic part in a fluidised bed were measured by a heat transfer probe developed in the present work. The structure of the probe was optimized with numerical simulation of energy conservation for measuring the heat transfer coefficient of 150-600 W/m2K. The relationship between the particle dynamics and the heat transfer was analysed to form the basis for future more rational designs of fluidised beds as well as for improved quality control.

The effect of conventional mechanical periodontal treatment on red complex microorganisms and clinical parameters in Down syndrome periodontitis patients: a pilot study

Periodontal disease (PD) is induced by a complex microbiota, such as Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola (together called the red complex), which triggers intense inflammatory reaction. Down syndrome (DS) individuals demonstrate a high prevalence of PD compared with those who are otherwise chromosomally normal (euploids). This pilot study aimed to evaluate the effect of non-surgical periodontal treatment in DS chronic periodontitis patients on clinical and microbiological parameters. Patients with chronic periodontitis, 23 DS and 12 euploids (control group), were submitted to non-surgical mechanical periodontal treatment, followed by maintenance for 45 days. Clinical parameters after periodontal treatment were similar in diseased and healthy sites, independent of the genetic background. Diseased sites of DS and control patients harbored similar levels of P. gingivalis and T. forsythia at baseline, but significantly higher levels of T. denticola were found in DS patients. Increased levels of P. gingivalis at healthy sites were found in DS individuals. Non-surgical periodontal therapy decreased the levels of red complex microorganisms and improved the tested clinical parameters of diseased sites in both groups. However, the levels of red complex bacteria were higher in diseased sites of DS patients after the periodontal treatment. We conclude in this pilot study that, although the mechanical periodontal treatment seemed to be effective in DS subjects over a short-term period, the red complex bacteria levels did not decrease significantly in diseased sites, as occurred in controls. Therefore, for DS patients, it seems that the conventional non-surgical periodontal therapy should be improved by utilizing adjuvants to reduce the presence of periodontopathogens.