Magnesium-based alloys are promising materials as next generation biodegradable implants, however low corrosion resistance and inadequate mechanical properties are limiting their application as a ...biodegradable implant material. In this study, Mg-Sr-Ca ternary alloys were prepared in a vacuum/atmosphere controlled furnace and coated by microarc oxidation (MAO) process for 5min to decrease the degradation rate and enhance the biocompatibility. Moreover, Ag doped Hydroxyapatite nano powder (Ag-HA) was also added to alkaline MAO solution by amount of 1 and 10g/l to improve the antibacterial properties while enhancing their bioactivity in a one single process. XRD, SEM-EDS, FTIR spectroscopy, simulated body fluid (SBF) immersion and antibacterial tests were employed for the characterization of the coated alloys. The results showed that, the addition of more Ag-HA increased the HA formation both before and after SBF immersion test and enhanced their antibacterial properties. However, Ag-HA addition decreased the corrosion resistance of the coated alloys in SBF compared to Ag-HA free coating. The results indicated that the present Ag-HA nano powder added MAO coating is a good combination to enhance the corrosion resistance, bioactivity and the antibacterial properties of Mg based biodegradable alloys.
•Silver doped Hydroxyapatite (Ag-HA) addition improved antibacterial properties.•HA morphology is related to Ag-HA content in the electrolyte.•The increase of Ag-HA content in the electrolyte increased the HA formation.•Increasing the Ag-HA concentration resulted in the Ca/P ratio approaching to 1.67.
In this study, oxide coatings produced on commercially pure Al via 40-min microarc oxidation process in electrolytes containing Na
2
SiO
3
, KOH and α-Al
2
O
3
powder were characterized by SEM-EDS, ...profilometry, XRD and microhardness tests. The addition of α-Al
2
O
3
particles into the electrolyte resulted in increased coating thickness and roughness. The coating thickness values of the samples varied between 35 and 135 µm. Increasing the amount of α-Al
2
O
3
particles in the electrolyte resulted in mechanical deposition/encapsulation of α-Al
2
O
3
particles and/or chemical reaction with constituents of the coatings. This chemical reaction increased the microhardness of the coatings and resulted in preferential growth of mullite (3Al
2
O
3
.2SiO
2
) crystal in the outer glassy region of the coatings. Outer regions of the coatings comprised 3Al
2
O
3
.2SiO
2
, γ-Al
2
O
3
and κ-Al
2
O
3
phases with chemically or mechanically bonded α-Al
2
O
3
particles, and in the inner regions were mostly γ-Al
2
O
3
and κ-Al
2
O
3
phases along with α-Al
2
O
3
phase formed through phase transformations.
The aim of this
study was to evaluate the changes in friction between orthodontic brackets and archwires coated with aluminum oxide (Al
O
), titanium nitride (TiN), or chromium nitride (CrN). In ...addition, the resistance of the coatings to intraoral conditions was evaluated.
Stainless steel canine brackets, 0.016-inch round nickel-titanium archwires, and 0.019 × 0.025-inch stainless steel archwires were coated with Al
O
, TiN, and CrN using radio frequency magnetron sputtering. The coated materials were examined using scanning electron microscopy, an X-ray diffractometer, atomic force microscopy, and surface profilometry. In addition, the samples were subjected to thermal cycling and
brushing tests, and the effects of the simulated intraoral conditions on the coating structure were evaluated.
Coating of the metal bracket as well as nickel-titanium archwire with Al
O
reduced the coefficients of friction (CoFs) for the bracket-archwire combination (
< 0.01). When the bracket and stainless steel archwire were coated with Al
O
and TiN, the CoFs were significantly lower (0.207 and 0.372, respectively) than that recorded when this bracket-archwire combination was left uncoated (0.552; p < 0.01). The friction, thermal, and brushing tests did not deteriorate the overall quality of the Al
O
coatings; however, some small areas of peeling were evident for the TiN coatings, whereas comparatively larger areas of peeling were observed for the CrN coatings.
Our findings suggest that the CoFs for metal bracket-archwire combinations used in orthodontic treatment can be decreased by coating with Al
O
and TiN thin films.
•Ni80Si20, Ni70Si30, Ni55Si45 and Ni45Si55 were prepared by arc melting method.•The maximum microhardness value of 1126HV obtained for Ni70Si30 alloy.•The microhardness values decreases with increase ...of Si/Ni ratio.•Ni80Si20 and Ni55Si45 are soft ferromagnetic, Ni70Si30 and Ni45Si55 are paramagnetic.
In the present work, Ni–Si eutectic alloys with nominal compositions of Ni80Si20, Ni70Si30, Ni55Si45 and Ni45Si55 (Ni and Si with the purity of 99.99%) were prepared by arc melting method under vacuum/argon atmosphere. The effects of Si/Ni ratio on the microstructural properties, thermal transformation behavior, micro-hardness and magnetic properties of the Ni–Si eutectic alloys were investigated. These alloys were characterized by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), differential thermal analysis (DTA), Vickers microhardness measurement and Vibrating Sample Magnetometer (VSM). The phases expected according to Ni–Si phase diagram for conventional solidified eutectic Ni–Si alloys are considerably consistent with phase detected by XRD in this study. The quantitative results confirm that the chemical composition of the alloys very close to eutectic compositions and the microstructures are in typical lamellar eutectic morphology. The maximum microhardness value of 1126HV obtained for Ni70Si30 alloy which has highest melting temperature amongst Ni–Si eutectics. The microhardness values decreases with increase of Si/Ni ratio. Ni80Si20 and Ni55Si45 alloys are soft ferromagnetic, Ni70Si30 and Ni45Si55 alloys are paramagnetic with no magnetic saturation.
In this work, Mg65Ni20Y15–XAgX (X = 1, 2, 3, 5) alloys were manufactured by atmosphere controlled induction system. The effect of Ag ratio on the microstructural properties, micro-hardness, density, ...and homogeneity of the Mg–Ni–Y alloys were investigated. These alloys were characterized by X-ray diffraction (XRD), optical microscopy, scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and Vickers micro-hardness measurement. According to XRD results, Ni3Y and Mg6Ni phases were observed as well as AgY and Ag17Mg54 phases, which were obtained in alloys. The quantitative results of EDX analysis confirm that the chemical composition of the obtained phases is very close and their homogeneities are so high. The average micro-hardness values of the ingot alloys were measured between 208 and 266 HV for matrix. The elastic modulus and densities of the Mg65Ni20Y15–XAgX (X = 1, 2, 3, 5) alloys increased by increasing Ag in the alloys and they were determined in the range of 58.18–68.12 GPa and 3.14–3.53 g/cm3, respectively.
The pure zirconium metal was coated by plasma electrolytic oxidation in silicate containing basic electrolyte for the cumulative periods of 5, 10, 20, 30, 45, 60, 90, and 120min successively for the ...total coating duration of 120min. The phase content, surface morphology and chemical composition of the PEO coating were characterized by XRD, SEM and profilometry after each coating time successively. The equiaxed clusters unique to Zr were formed on the surface of the coating. The number of plasma channels decreased but the sizes and intensities of the sparks increased by increasing the process duration and consequently the amount of materials ejaculated through these channels increased. The thickness and the surface roughness of the coating were increased by the process duration. The presence of cracks and pores resulted in a lower value of microhardness of the coating compared to the theoretical value of ZrO2. The plasma channels containing Si rich and radially grown Zr rich crystals were clearly observed from the cross sectional examination of intentionally created fracture surface. The characterizations carried out upon successive coating and successive removal of this coating confirmed that monoclinic ZrO2/tetragonal ZrO2 ratio was not changing with coating thickness.
•Monoclinic ZrO2 and tetragonal ZrO2 phases were the main constituents of the coating.•Monoclinic ZrO2/tetragonal ZrO2 ratio doesn't depend on PEO coating thickness.•Plasma channels were revealed by cross-sectional fracture surfaces.•The equiaxed clusters unique to Zr were formed on the surface of the coating.
The Al–Si binary alloys were prepared in an atmosphere controlled furnace with the addition of 1, 2, 4, 8, 12, 16 and 32at.% Si. The alloys were coated by microarc oxidation process for 120min in a ...basic electrolyte containing silicate. X-Ray Diffraction, scanning electron microscope-energy dispersive X-ray spectroscopy, profilometry and Vickers microhardness tester were employed for the characterization of the coatings. The coating thickness, average microhardness and surface roughness decreased with an increase of Si content in the substrates. α-Al2O3 phase was formed in the inner region of the coating of Al–Si alloys with 1–2at.% Si while all coatings were composed of mullite and γ-Al2O3 phases along with the amorphous phase. The coating surface became smoother, the glassy regions and number of porosities with finer sizes increased with the increase of Si content in the alloys. The Si concentration was relatively higher at the most outer and inner regions of the coating and it was approximately constant in the other parts of the coatings. The entrapped volume of porosities in the coatings increased with the Si content of the substrates.
•The coating thickness decreased with Si addition into substrate.•The formation α-Al2O3 was suppressed with Si content in the substrates.•The increase in amount of Si in the substrate resulted in a smoother surface.•Mullite and γ-Al2O3 phases existed on all coatings.•α-Al2O3 phase was only detected on coating of alloys with 1–2at.% Si.
► The coating thickness increased with Zn addition into substrate. ► The formation α-Al2O3 was suppressed and consequently hardness value of the coatings decreased with Zn content in the substrates. ...► The increase in amount of Zn in Al, resulted in a rougher surface. ► Mullite and γ-Al2O3 phases existed on all coatings. α-Al2O3 phase was also detected on coated pure Al and Al–Zn alloys with 1–10wt.% Zn.
The synthetic Al–Zn binary alloys were prepared in a vacuum/atmosphere-controlled furnace with the addition of 1, 4, 8, 10, 15 and 33wt.% Zn. The alloys and pure Al were coated by microarc oxidation in the electrolyte containing sodium silicate and potassium hydroxide for 120min. XRD, scanning electron microscope (SEM)–energy-dispersive X-ray spectroscopy (EDS), profilometry and Vickers microhardness measurements were employed for the characterization of the coating. The higher amount of Zn in the substrate promoted the formation of porous coating. The outer regions of all coatings were loose and weak, while the inner regions were relatively denser and harder. The features on the coating surface became coarser with the increase of Zn content in the alloys, which resulted in the increase of surface roughness from 9.3μm to 12.5μm. The coating thickness increased from 80μm to 120μm with the increase of Zn content in the substrates. Mullite and γ-Al2O3 phases were formed on all coatings and α-Al2O3 phase was also formed on coated pure Al and Al–Zn alloys with 1–10wt.% Zn. Increasing amount of Zn in the Al–Zn alloys suppressed α-Al2O3 formation and reduced the microhardness of the coatings. The Zn concentration was constant throughout the coating for the alloys with lower amount of Zn, though it decreased gradually from interface to surface for the alloys containing higher amount of Zn.
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