Effects Of Pretreatments On Microstructures And Performances Of Micro-arc Oxidation Coatings On Pure Titanium Surfaces

This paper studies titanium micro-arc oxidation process and growth rules of its oxide coatings, analyzes reaction mechanisms of micro-arc oxidation on titanium matrix and establish the models of coating growth and treatment process using JEOL JEM-2100High Resolution Transmission Electron Microscope (HRTEM), HITACHI SU-70Field Emission Scanning Electron Microscopy (FE-SEM), MicroNano Multi-mode Scanning Probe Microscopy (MSPM), Rigaku D/max-rc X-ray diffraction (XRD), FTIR-8400Fourier Transform Infrared Spectrometer (FTIR), EG&G Princeton PAR2273Electrochemical Workstation and etc. advanced research tools;to discuss the effects of different pretreatments on the complex preparations in micro-arc oxidation, the paper also systematically studies sandblasting, etching, sandblast-etching (blast-etching) surface pretreatments on titanium samples and their micro-arc oxidation coatings through the "Design-of-complex-preparation-optimization-of-process-condition" methods, deeply analyzes the surface microstructures, phase compositions, bonding strength, mechanical properties, wettability and corrosion resistance of the sandblasted, etched, blast-etched titanium specimen surfaces and their micro-arc oxidation coatings as well as the samples prepared by assistant conditions of ultrasound and low temperature, comparing the hydroxyapatite (HA)-inducing ability and the animal in vivo/vitro test. The achieved conclusions include:The titanium micro-arc oxidation coating surfaces’morphology, microroughness, hardness, weigh, thickness, phase and element composition vary with different oxidation time correspondingly, and the micro-arc oxidation coatings finish growing on pure titanium at20min. The models of titanium micro-arc oxidation process indicate certain links between the microstructures or phase compositions of oxide coatings and the process parameters, in which the treatment time t is the most necessary one, and it determines the intensity of oxidation process, affecting the coatings’ microstructures and the other parameters. In addition, titanium micro-arc oxidation coating also exhibits a capacitive effect.The surface of sandblasted titanium substrate performs a better combination of microroughness and hardness at the blasting intensity of45s. The titanium substrate and its oxide film are etched in the mixed HF-HCI-solution, being influenced on its microstructure and mechanical properties, and the surface of etched titanium substrate shows a distinct combination of α-β-phase structure at the etching intensity of90s. Afer titanium substrates are pretreated with complex preparations, the micro-arc oxidation coating on sandblasted substrate completes in25min, while it on acid-etched substrate completes in15min. The micro-arc oxidation coatings on differently pretreated titanium substrates perform varied surface microstructures, mechanical properties, coating thicknesses and weights as well as varied phase structures and elemental compositions, and especially perform bonding strength, wettability, corrosion resistance or other properties describing that the pretreatments has a significant influence on the titanium samples.Blast-etching mainly produces a compound function on the titanium samples. When the substrate is sandblasted for45s and etched for120s, its so-prepared surface synthesizes a complex effect of the combined sandblasting and acid-etching, being got rid of the sandblasting residuals. The test results of characterization and properties of the coatings prepared in different assistant conditions show that the micro-arc oxidation coating on blast-etched titanium substrate in ultrasonic assistant condition has a more uniform surface microstructure, bigger micropore size, higher contents of Ca3(PO4)2and Ca, P elements together with a higher wettability and bonding strength, indicating it suitable for the contact with bone tissues; while the micro-arc oxidation coating on blast-etched titanium substrate in low-temperature assistant condition has a smaller surface microroughness and micropore size, improving corrosion resistance without reduced wettability and bonding strength, therefore indicating it suitable for the contact with soft tissues.When the titanium micro-arc oxidation samples which are prepared by different pretreatments and assistant conditions soak in simulated body fluid (SBF) and are mineralized biomimetically, they deposit varied morphologies and weights of HA layers, in which the blast-etched titanium substrate exhibits the best HA-inducing ability. It is found favourable bioacivities and biocompatibilities that L929fibroblast adhesion, morphology of filopodia and its proliferation on prepared titanium samples, as well as the appearance of their subcutaneous implantation and soft tissue biopsies in rats.