Hardness and elastic modulus of TiO₂ anodic films measured by instrumented indentation

Abstract

The aim of this work was to investigate the mechanical properties of the titanium anodic films (TiO2) produced by anodic oxidation under galvanostatic conditions, using a 1.4M phosphoric acid electrolyte, with different current densities (J) on commercially pure titanium (cp-Ti). The morphology of the oxide films were observed by scanning electron microscopy (SEM), whereas the composition of the film was determined by Raman spectroscopy. Porosity, average roughness (Ra) and thickness of the TiO2 films increased with the applied J. Hardness and elastic modulus were measured by instrumented indentation technique, and the influence of the substrate was corrected using analytical models. The anodic films presented higher hardness and lower elastic modulus values compared with the cp-Ti.

Nanomechanical and nanotribological properties of bioactive titanium surfaces prepared by alkali treatment

“…Besides, yield strength is usually determined by its linear relationship with hardness, which we aim to determine in the present work. Soares et al (2008) suggested a relation between yield strength and plasticity index, however, it is valid only for rigid surfaces such as ceramic oxides. Since Kim et al (1997b) reported that the film thickness increases with the alkali treatment period, we employed an alternative method using a thicker film produced by alkali treatment for 72 h and regular heat treatment (AHT-72).…”

Tribo-mechanical characterization of rough, porous and bioactive Ti anodic layers

“…The index f indicates the layer and s indicates the substrate. The above equation is valid for the situation where the layer is harder than the substrate, which is applicable in anodic layers (Santos Jr. et al, 2007;Soares et al, 2008). The Bhattacharya and Nix model has been presented as a satisfactory choice to obtain the layer hardness (Fischer-Cripps, 2004 Since the layer hardness is the concern of this study, a different approach is needed for the layer yield strength Y f .…”

“…The Poisson's ratio for Ti is well known (ν = 0.32). For the titania layers it was assumed that ν = 0.28 (Soares et al, 2008). Calculations were performed for all points constituting the composite profiles, since they lay inside the layer region (depths up to 3 µm).…”

“…Instrumented indentation is an appropriate method to mechanically characterize thin coatings and modified surfaces (Oliver and Pharr, 2004), and it has been used in the study of bioactive layers (Santos Jr. et al, 2007;Soares et al, 2008). However, the determination of the elastic modulus (E) and hardness (H) of the porous anodic layers is not simple.…”

Plasma Sprayed Bioceramic Coatings on Ti-Based Substrates: Methods for Investigation of Their Crystallographic Structures and Mechanical Properties

“…Therefore, the bioceramic coatings and calcium orthophosphates in particular, applied on Ti-based substrates, having a useful combination of biocompatibility, mechanical properties and relative stability in bodily environment, are subjects of an increasing interest for biomedical applications in modern orthopaedics and dentistry (Gaona et al, 2007;Salman et al, 2008;Soares et al, 2008;Thomas, 1994).…”