Parameter Optimization in Cluster Identification Algorithms for Characterizing Nanoclusters in Al-Mg-Si-Cu Alloys.

Optimization of user-defined parameters (Dmax, Nmin, order (K)) in the Density-based Spatial Clustering of Applications with Noise (DBSCAN) algorithm, used to characterize nanoclusters in Al-0.9% Mg-1.0% Si-0.3% Cu (mass %), was conducted. Ten combinations of parameters with a given K were considered for samples naturally aged (NA) and preaged (PA) at 100°C. We confirmed four types of unphysical clusters, artificially formed, by analyzing composition with size, atomic density, and atomic arrangement inside clusters. The optimum combinations minimizing those unphysical clusters were obtained for both NA and PA samples. Meanwhile, to evaluate the reliability of the optimum combination, volume rendering and isosurfacing were performed. As a result, regions of high solute concentration were confirmed, and those regions are in good agreement with the position of the clusters obtained by applying the optimum combination in DBSCAN. Furthermore, by comparing the optimum combinations with the fixed parameters widely used until now, we showed that for each dataset, considering independent parameters obtained in the same method is desirable rather than using fixed parameters. Consequently, an idea of determining the algorithm parameters for characterizing the nanoclusters in Al-Mg-Si(-Cu) alloys was introduced.

In vitrocellular biocompatibility andin vivodegradation behavior of calcium phosphate-coated ZK60 magnesium alloy.

Calcium phosphate (Ca-P) surface coating is a simple but effective way to enhance both corrosion resistance and biocompatibility of ZK60 magnesium alloy. However, cell compatibility on different Ca-P layers coated on ZK60 alloy has seldom been investigated. In this study, the effects of type, morphology and corrosion protection of several Ca-P coatings formed at pH 6.5, 7.8 and 10.2 on cell behavior were examined by using an osteoblastic cell line MC3T3-E1. Furthermore,in vivobehavior in rabbits of the alloy coated with the optimum Ca-P layer was also studied. It was found that the surface factors governed the cell morphology and density. The coating morphology plays a dominant role in these surface factors. The sample coated at pH 7.8 showed the best cellular biocompatibility, suggesting that the hydroxyapatite (HAp) layer formed at pH 7.8 was the optimum coating. In rabbits, this optimum coating enhanced remarkably the corrosion resistance of the alloy. During implantation, the outermost crystals of the HAp coating were shortened and thinned due to the dissolution of HAp caused by the body fluid of the rabbits. It is indicated that ZK60 alloy coated at pH 7.8 can be applied as a biodegradable implant.

Data on atomic structures of precipitates in an Al-Mg-Cu alloy studied by high resolution transmission electron microscopy and first-principles calculations.

The dataset refers to the research article "Precipitation processes and structural evolutions of various GPB zones and two types of S phases in a cold-rolled Al-Mg-Cu alloy" [1]. Transmission electron microscopy (TEM) and density functional theory (DFT) were used to investigate precipitates in an Al-Cu-Mg alloy aged at 443 K for various times. High-angle annular dark-field scanning TEM (HAADF-STEM) images in <100> Al orientations were analyzed. Characteristic contrast and symmetries of columns [2] yielded atoms and positions, used to build precipitate models which could be refined and compared with solid solution reference energies. A calculation cell is an Al supercell compatible with symmetry and morphology of a precipitate, which is fully or partly surrounded by Al, allowing periodicity continuation via neighbor cells. The given crystallographic data include two S-phase variants and Guinier-Preston-Bagaryatsky (GPB) zones, of which the "GPBX" is new.

Enhanced Corrosion Resistance and In Vitro Biocompatibility of Mg-Zn Alloys by Carbonate Apatite Coating.

B-type carbonate apatite (CAp) coatings were formed on as-cast and T4-treated Mg-xZn (x = 1, 5, and 7 wt %) alloys containing various sized Zn-rich second phase to improve the corrosion resistance and biocompatibility. The CAp coating grew uniformly on the alloys with a thickness of 1.1-1.3 µm and did not show cracks or pores on 30 µm-sized second-phase particles. The CAp coating retarded corrosion of Mg-Zn substrates for the first 3-5 days in Hanks' solution. Polarization resistance of the CAp-coated alloys was 10-90 and 1-70 times higher than the uncoated and hydroxyapatite (HAp)-coated alloys, respectively. The corrosion rate of CAp-coated alloys was greatly affected by the substrate alloys once the coatings were partly broken. The CAp-coated alloys showed 40-60 and 25-45% lower 14-day average corrosion rates than the uncoated and HAp-coated alloys, respectively, in the immersion test. The CAp coating significantly enhanced the viability of osteoblastic MC3T3-E1 cells on the Mg-Zn alloys for 72 h compared to the uncoated and HAp-coated alloys. The cell densities on CAp-coated alloys were similar for 72 h regardless of substrate alloys. Therefore, the CAp coating can be a superior coating candidate for corrosion-control and biocompatibility improvement for biodegradable Mg alloys.

In Vitro Corrosion and Cell Response of Hydroxyapatite Coated Mg Matrix in Situ Composites for Biodegradable Material Applications.

In this study, hydroxyapatite (HAp) coated Mg matrix composites were fabricated for biodegradable implant applications. Spark plasma sintering was employed to fabricate the Mg-10 wt% ZnO composite substrates. HAp was coated on the surface of the sintered composites and pure Mg by a chemical solution treatment. SEM and optical micrographs of coated samples showed that HAp grew homogeneously and formed a layer on the entire surface of both pure sintered Mg and Mg composites. The immersion and polarization test results demonstrated that the HAp coating significantly improved the corrosion resistance of the sintered composites. While the HAp coating layer is not effective in the improvement of the pure Mg substrate, cell culture test results revealed that the HAp coating improved cell adhesion and proliferation on the composites effectively through 72 h, while no cell could survive on the uncoated composites after 72 h. In addition, the corrosion tests and cell culture test results indicated that the composite with longer sintering time has better corrosion resistance and cell viability than those of the composite with shorter sintering time. The findings suggested that the HAp-coated Mg-10 wt% ZnO-2.5 h + 10 min composite is a high-potential candidate for biodegradable implant applications.

Degradation behaviors and cytocompatibility of Mg/ß-tricalcium phosphate composites produced by spark plasma sintering.

Magnesium (Mg)-based materials have shown great potentials for bioresorbable implant applications. Previous studies showed that Mg with 10 and 20 vol % ß-tricalcium phosphate (ß-TCP) composites produced by spark plasma sintering, improved mechanical properties when compared with pure Mg. The objectives of this study were to evaluate the degradation behaviors of Mg/10% ß-TCP and Mg/20% ß-TCP composites in revised stimulated body fluid (rSBF), and to determine their cytocompatibility with bone marrow derived mesenchymal stem cells (BMSCs) using the direct culture method. During the 11 days of immersion in rSBF, Mg/ß-TCP composites showed different degradation behaviors at different immersion periods, that is, the initial stage (0-1 hr), the mid-term stage (1 hr to 2 days), and the long-term stage (2-11 days). The counter effects of mass loss due to microgalvanic corrosion and mass gain due to deposition of Ca-P containing layers resulted in slower Mg2+ ion release for Mg/20% ß-TCP than Mg/10% ß-TCP in the mid-term, but eventually 16% mass loss for Mg/20% ß-TCP and 10% mass loss for Mg/10% ß-TCP after 11 days of immersion. The in vitro studies with BMSCs showed the highest cell adhesion density (i.e., 68% of seeding density) on the plate surrounding the Mg/10% ß-TCP sample, that is, under the indirect contact condition of direct culture. The ß-TCP showed a positive effect on direct adhesion of BMSCs on the surface of Mg/ß-TCP composites. This study elucidated the degradation behaviors and the cytocompatibility of Mg/ß-TCP composites in vitro; and, further studies on Mg/ceramic composites are needed to determine their potential for clinical applications. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2238-2253, 2019.

Influence of Si Addition on Quenching Sensitivity and Formation of Nano-Precipitate in Al-Mg-Si Alloys.

The age-hardening is enhanced with the high cooling rate since more vacancies are formed during quenching, whereas the stable beta phase is formed with the slow cooling rate just after solid solution treatment resulting in lower increase of hardness during aging. Meanwhile, the nanoclusters are formed during natural aging in Al-Mg-Si alloys. The formation of nanoclusters is enhanced with increasing the Si amount. High quench sensitivity based on mechanical property changes was confirmed with increasing the Si amount. Moreover, the nano-size beta" phase, main hardening phase, is more formed by the Si addition resulting in enhancement of the age-hardening. The quench sensitivity and the formation behavior of precipitates are discussed based on the age-hardening phenomena.

Electrochemical processes of nucleation and growth of calcium phosphate on titanium supported by real-time quartz crystal microbalance measurements and X-ray photoelectron spectroscopy analysis.

Real-time, in situ electrochemical quartz crystal microbalance (EQCM) measurements are conducted to better understand the electrocrystallization of calcium phosphates (CaP) on CP-Ti. X-ray photoelectron spectroscopy is used to identify the exact phase deposited, so that reliable estimation of the electrochemical processes involved is made. Analysis of the integrated intensity of the oxygen shake-up peaks, in combination with the determination of Ca/P and O/Ca atomic ratios, enables to determine unambiguously that the octacalcium phosphate (OCP) is formed. Its role as a precursor to hydroxyapatite (HAp) is discussed. After an incubation period, the process by which OCP is formed follows a Faradaic behavior. The incubation time may be related to the need for local increase of pH before precipitation from solution can occur. The standard enthalpy of activation is approximately 40 kJ/mol, which excludes diffusion-controlled processes from being rate determining. The OCP deposit has thickness approximately 0.61 microm, apparent density approximately 0.95 g/cm3, 63.6% porosity, and deposition rate of 23.5 ng/(cm2 s) or 15 nm/min. The low-equivalent weight value of 20.5 g/equiv, and the associated remarkably high number of electrons transferred in the reaction n approximately 24, indicates that most of the current is consumed either by electrolysis of water or by a complex set of parasitic reactions. The low-solubility product allows precipitation of CaP even at relatively low concentrations of calcium and phosphate/hydrogen phosphate ions. It is shown that HAp most likely forms via transformation of precursor phases, such as OCP, rather than directly.

Comparative study on torsional strength, ductility and fracture characteristics of laser-welded alpha+beta Ti-6Al-7Nb alloy, CP Titanium and Co-Cr alloy dental castings.

OBJECTIVES: The purpose of this study was to compare torsional strength, ductility and fracture behaviors of Ti-6Al-7Nb, CP Ti and Co-Cr alloy castings after laser welding. METHODS: Dumbbell-shaped castings of three metal alloys (Ti-6Al-7Nb alloy, CP Ti, Co-Cr alloy) were cut in half and laser welded with a Nd:YAG pulse laser-welding machine at either 220V or 260V of laser voltage. After being laser welded, all cast specimens were tested with a multi-axial hydraulic testing machine (MTS 858 Mini Bionix) using a torsional test. The fracture surfaces were investigated with a scanning electron microscope. RESULTS: None of the laser-welded Ti-6Al-7Nb alloy and CP Ti castings was broken within the welded joint, showing torsional strength as high as the unwelded castings. Unlike the other groups, the laser-welded Co-Cr alloy castings exhibited brittle fracture appearance and provided substantially less torsional strength. SIGNIFICANCE: The torsional strength of the laser-welded Ti-6Al-7Nb alloy and CP Ti castings was as high as that of the unwelded castings while this finding could not apply to the Co-Cr alloy castings. This indicates that the mechanical strength of the laser-welded Ti-6Al-7Nb alloy dental casting is sufficient for clinical applications.

Structure and strength at the bonding interface of a titanium-segmented polyurethane composite through 3-(trimethoxysilyl) propyl methacrylate for artificial organs.

The objective of this study was to investigate the structure and strength at the bonding interface of a titanium (Ti)-segmented polyurethane (SPU) composite through (3-trimethoxysilyl) propyl methacrylate (gamma-MPS) for artificial organs. The effects of the thickness of the gamma-MPS layer on the shear bonding strength between Ti and SPU were investigated. Ti disks were immersed in various concentrations of gamma-MPS solutions for several immersion times. The depth profiles of elements and the thickness of the gamma-MPS layer were determined by glow discharge optical emission spectroscopy and ellipsometry, respectively. The bonding stress at the Ti/gamma-MPS/SPU interface was evaluated with a shear bonding test. Furthermore, the fractured surface of a Ti-SPU composite was observed by optical microscopy and characterized using X-ray photoelectron spectroscopy. Consequently, the thickness of the gamma-MPS layer was controlled by the concentration of the gamma-MPS solution and immersion time. The shear bonding stress at the interface increased with the increase of the thickness of the gamma-MPS layer. Therefore, the control of the thickness of the gamma-MPS layer is significant to increase the shear bonding stress at the Ti/gamma-MPS/SPU interface. These results are significant to create composites for artificial organs consisting of other metals and polymers.

Mechanical strength and microstructure of laser-welded Ti-6Al-7Nb alloy castings.

Mechanical properties of laser-welded castings of Ti-6Al-7Nb alloy, CP Ti, and Co-Cr alloy were investigated and compared to the unwelded castings using a tensile test. Dumbbell-shaped specimens were cut at the center, and two halves of the specimens were welded with an Nd:YAG laser welding machine at 220 or 260 V of laser voltage. The mechanical strength of 260 V groups was higher than that of 220 V groups for Ti-6Al-7Nb and Co-Cr alloys except for CP Ti. All 260 V laser-welded castings of Ti-6Al-7Nb alloy and CP Ti, which fractured outside the welded joints, exhibited ductile characteristics, while all laser-welded Co-Cr alloy castings, which fractured within the welded joints, showed brittle characteristics. This study proved that the mechanical strength of laser-welded Ti-6Al-7Nb alloy and CP Ti castings was as high as that of unwelded castings, while the mechanical properties of laser-welded alloy joints were influenced by microstructural changes.

Deformation properties of Ti-6A1-7Nb alloy castings for removable partial denture frameworks.

Ti-6Al-7Nb alloy was cast into three differently designed, removable partial denture frameworks: Palatal strap (PS), Anterior-posterior bar (AP), and Horseshoe-shaped bar (HS). The vertical displacement and local strain of Ti-6Al-7Nb alloy frameworks were investigated to compare against those of Co-Cr alloy frameworks. Vertical loading force of 19.6 N was applied at two locations, 10 and 20 mm, from the distal end of the framework. Although higher vertical displacement and local strain were observed for Ti-6Al-7Nb alloy frameworks than those for Co-Cr alloy frameworks, the PS framework appeared to show the least deformation. In addition, the strain at 10-mm location was higher than that at 20-mm location for AP and HS frameworks. This study thus proved that design had a significant influence on the deformation properties of denture frameworks. The PS design was evaluated to be a suitable design for the removable denture framework with Ti-6Al-7Nb alloy.