Effect of microstructural evolution on wettability and tribological behavior of TiO2 nanotubular arrays coated on Ti–6Al–4V

Self-organized TiO2 nanotubular arrays were fabricated by electrochemical anodization of Ti–6Al–4V plates in an NH4F/H3PO4 electrolyte. The effect of microstructural evolutions on the wettability and tribological behavior of the TiO2 nanotubes was investigated. Based on the XRD profiles of the fabricated material, the characteristic TiO2 peaks were not recognized after anodization; however, highly crystalline TiO2 (anatase and rutile) was formed due to crystallization during annealing at 500 C for 1.5 h. The nanotube arrays were converted entirely to rutile at 700 C. From a microstructure point of view, a highly ordered nanotube structure was achieved when the specimen was annealed at 500 C, with a length of 0.72 μm and a pore diameter of 72 nm. Further increasing the annealing temperature to 700 C resulted in the complete collapse of the tubular structure. The results indicate that the improved wettability of the anodized specimens was due to the combination of the effects of both the surface oxide layer and the increased surface roughness achieved after anodization. Moreover, the wear resistance and wettability of the sample annealed 500 C were improved due to the high hardness (435 HV) and low coefficient of friction (0.133–168) of the highly crystalline structure of the TiO2 nanotubes.Ministry of Higher Education, Malaysia with the high impact research grant no. of M.C/HIR/MOHE/ENG/27 and partly sponsored by UM.TNC/IPPP/UPGP/638/PPP/PG121-2012B and UM.TNC2/RC/AET/261/1/1/RP017-2012

Self-organized TiO2 nanotube layer on Ti–6Al–7Nb for biomedical application

In the present study, a self-organized nanotube TiO2 layer on Ti–6Al–7Nb was fabricated. The influence of acidic electrolytes including glycerol (G) and ethylene glycol (EG) on the anodization, microstructural features and surface wettability was explored. The phase compositions and morphological characteristics were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. According to the results, due to the intrinsic amorphous feature of ceramic oxide, the characteristic TiO2 peaks were not detected in the XRD profiles. After annealing in normal atmosphere at 600 °C for 2 h, TiO2 crystallized and consequently, nanotubular TiO2 arrays containing anatase and rutile phases formed. From a microstructural point of view, the average length and diameter of the nanotube array ranged from 2.23 to 4.22 μm and 160 to 170 nm, respectively. Besides, the type of acidic electrolyte and subsequent annealing noticeably affected the surface wettability of the products.University of Malaya, grant Nos.: UM TNC2/RC/261/1/1/RP021C-13AET and HIR UM.C/HIR/MOHE/ENG/2

Vertically oriented ZrO2[sbnd]TiO2[sbnd]Nb2O5[sbnd]Al2O3 mixed nanopatterned bioceramics on Ti6Al7Nb implant assessed by laser spallation technique

Recently, reports on the fabrication of nonstructural configuration have generated scientific interest due to increased awareness of the oxide nanotubes in the biomedical implant field and other industrial approaches. Here, highly ordered ZrO2[sbnd]TiO2[sbnd]Nb2O5[sbnd]Al2O3 nanotube arrays were grown by physical vapor deposition (PVD) of a zirconium layer on titanium-niobium alloy implant (IMPTi67) and succeeding anodic oxidation at a constant voltage (60 V) with exposure times ranging from 30 to 300 min. To crystallize the resulting mixed oxide nanotubes, heat treatment was also applied. The nanotubes were placed in an atmospheric furnace at temperatures ranging from 450 to 800 °C for 2 h. This treatment provided a morphological evolution was strongly influenced by the anodization time, where highly aligned bamboo-shaped oxide nanotubes (161 ± 44 nm in inside diameter and ∼1 μm in length) were formed after 300 min of anodization. After annealing at temperature below 500 °C, the nano-array configuration remained stable and the average inner diameter decreased to around 40 nm. The effects of anodically fabrication time on the adhesion strength of four-phase multilayered mixed oxide nanotubes on anodized Zr/IMPTi67 surfaces assed by microscratch analysis. From the results, increasing the annealing temperature further to 800 °C fully destroyed the nanotubes and consequently the tubular arrangement was converted to a coarse grain structure. It was revealed that annealing at 450 °C for 2 h was the optimum conditions for stable nanotubular array generation, where the highest adhesion strength (shifted from 2595.59 to 2640.12 mN), microhardness (372 HV) and hydrophilicity (15 ± 1°) were recorded. It is notify that the adhesion strength of highly ordered mixed nanotubes was remarkably decreased after thermal treatment at 800 °C (1817.51 mN). Through the laser spallation analysis, the intrinsic adhesion strength of the Zr/IMPTi67 interface was found to be at 63 MPa, while the first stages of failure occurred at a stress state of 35 MPa. The adhesion of the film with the tubular structure proved to have a significantly larger adhesion strength of 246 MPa for the complete failure and 203 MPa for incipient stages of spallation. The considered surface modification can be an effective step in determining the interface strength between biomedical implants and the nanostructured coatings

Effect of Heat Treatment on the Electrochemical and Mechanical Behavior of the Ti6Al4V Alloy

The effects of heat treatment on the hardness and electrochemical behavior of the Ti6Al4V alloy were studied. Two heat treatments were performed: one below (800 °C) and the other above (1050 °C) its beta transformation temperature (T= 980 ± 20 °C) and cooled using three conditions: water quenching, normalizing, and furnace. A microstructure observed using Optical Microscopy showed dependence on the heat treatment temperature applied; mainly three microstructures were obtained: martensitic, globular, and lamellar. Besides, alpha and beta phases were characterized by X-ray diffraction (XRD) technique. The Berkovich tests were performed to measure the hardness and reduced modulus (E). The Ti6Al4V alloy treated at 1050 °C and air-cooled exhibited hardness values closer to those of the Ti6Al4V as-received alloy. Electrochemical tests were carried out to analyze the electrochemical behavior after 7-day immersion in Hank’s solution at 37 °C and pH 7.40. Open Circuit Potentials (E) showed less negative values for Ti6Al4V and Ti6Al4V alloys, suggesting ennoblement of these materials. Furthermore, these alloys exhibited an outstanding electrochemical behavior compared to the Ti6Al4V as-received alloy by Electrochemical Impedance Spectroscopy (EIS) technique.The authors thank David Pérez-Risco for sharing his experience and useful advice on Berkovich Nano-indenter at the National Metallurgical Research Center (CENIM-CSIC Madrid, Spain), allowing this work to be carried out. Mercedes Paulina Chávez-Díaz thanks the National Science and Technology Council (CONACyT) for a doctoral fellowship to hold a research stay at CENIM-CSIC. This work was supported by the Government of Spain, through the Ministry of Economy and Competitiveness [MAT2015-67750-C3-1]. Elsa Miriam Arce-Estrada and Román Cabrera-Sierra wish to thank the National Research System (SNI) for the distinction of its members and the stipend received