Enhancement in sustained friction and wear resistance of nanoporous aluminum oxide films obtained by controlled electrochemical oxidation process

Comparison of the frictional resistance and optical properties of aluminum oxide and zinc oxide coated nickel titanium archwires – An in vitro study

Objectives:

The friction that appears during sliding mechanics poses a clinical challenge to the orthodontist. The primary focus of an ideal tooth movement is to reduce the friction created at the archwire-bracket interface. Various variables (both biological and mechanical) affect the role of friction during orthodontic tooth movement. One among the variables which play a critical role is the archwire used in fixed mechanotherapy. Nickel-titanium (NiTi) archwires are widely used in clinical conditions due to their properties such as low force delivery and wider elastic working range. Innovations in the field of material science have led to the evolution of nickel titanium archwires with coating and surface modification to enhance the esthetics and decrease friction. Esthetics is of major concern in patients undergoing orthodontic treatment. As the esthetic demand keeps rising, the need for developing an esthetically acceptable material is required and it should not compromise on the clinical performance. The study aimed to evaluate and compare the frictional resistance and optical properties of ALUMINIUM oxide and zinc oxide-coated Ni-Ti archwires.

Material and Methods:

The archwires were divided into three groups (n = 10), respectively: Group 1 – control group of uncoated NiTi archwires, GROUP 2 – zinc oxide coated NiTi archwires, and Group 3 – ALUMINIUM oxide coated NiTi archwires. The frictional resistance test was done using a universal testing machine, Instron, and optical properties were assessed using a colorimeter. The analysis of variance was used to determine whether a significant difference existed between the groups and a further post hoc Tukey test was used to determine the significant difference in the mean (P < 0.05).

Results:

The two coated archwire groups – zinc oxide and ALUMINIUM oxide archwires showed a significant decrease in frictional resistance. Of the three groups, zinc oxide showed the least frictional resistance compared to the ALUMINIUM oxide-coated group and the uncoated group. Optical properties were calculated using the formula ΔE*ab for the three groups. Of which zinc oxide coated archwires were closest to VA1 indicating that it matches the shade of the natural tooth while the other two groups did not match the tooth color implying that it is not much esthetic as that of zinc oxide coated archwires.

Conclusion:

The zinc oxide-coated archwire resembles tooth color as well as has less frictional resistance compared to the other archwires.

Dry Sliding Behavior of an Aluminum Alloy after Innovative Hard Anodizing Treatments

This work evaluates the dry sliding behavior of anodic aluminum oxides (AAO) formed during one traditional hard anodizing treatment (HA) and two golden hard anodizing treatments (named G and GP, respectively) on a EN AW-6060 aluminum alloy. Three different thicknesses of AAO layers were selected: 25, 50, and 100 μm. Prior to wear tests, microstructure and mechanical properties were determined by scanning electron microscopy (VPSEM/EDS), X-ray diffractometry, diffuse reflectance infrared Fourier transform (DRIFT-FTIR) spectroscopy, roughness, microhardness, and scratch tests. Wear tests were carried out by a pin-on-disc tribometer using a steel disc as the counterpart material. The friction coefficient was provided by the equipment. Anodized pins were weighed before and after tests to assess the wear rate. Worn surfaces were analyzed by VPSEM/EDS and DRITF-FTIR. Based on the results, the GP-treated surfaces with a thickness of 50 μm exhibit the lowest friction coefficients and wear rates. In any case, a tribofilm is observed on the wear tracks. During sliding, its detachment leads to delamination of the underlying anodic aluminum oxides and to abrasion of the aluminum substrate. Finally, the best tribological performance of G- and GP-treated surfaces may be related to the existence of a thin Ag-rich film at the coating/aluminum substrate interfaces.

Improving the Tribological Performance of MAO Coatings by Using a Stable Sol Electrolyte Mixed with Cellulose Additive

In this study, micro-arc oxidation (MAO) of aluminum 6061 alloy was carried out within a silicate base electrolyte containing 0.75 g/L of cellulose, and the tribological properties of the coating were investigated. The as-prepared coating was detected by Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), a scanning electron microscope (SEM) and an energy-dispersive spectrometer (EDS), respectively. The results suggested that cellulose filled in the microcracks and micropores, or it existed by cross-linking with Al3+. In addition, it was found that the cellulose had little effect on the coating hardness. However, the thickness and roughness of the coating were improved with the increase in cellulose concentration. Moreover, the ball-on-disk test showed that the friction coefficient, weight loss and wear rate of the MAO coating decreased with the increase in cellulose concentration. Further, the performances of the coatings obtained in the same electrolyte, under different preserved storage periods, were compared, revealing that the cellulose was uniformly dispersed in the electrolyte and improved the tribological properties of the MAO coating within 30 days.