In vitro characterisation of plasma-sprayed apatite/wollastonite glass-ceramic biocoatings on titanium alloys

Some ceramics have the ability to form direct bonds with surrounding tissues when implanted in the body. Among bioactive ceramics, the A/W (Apatite/Wollastonite) glass-ceramic, containing apatite and wollastonite crystals in the glassy matrix, has been largely studied because of good bioactivity and used in some fields of medicine, especially in orthopaedics and dentistry. However, medical applications of bioceramics are limited to non-load bearing applications because of their poor mechanical properties. In this study, A/W powders, obtained from industrial and high grade quality raw materials, were thermally sprayed by APS (atmospheric plasma spraying) on Ti-6Al-4V substrates, in order to combine the good bioactivity of the bioceramic and the good mechanical strength of the titanium alloy base material. The microstructure and the resulting properties were evaluated depending on processing parameters and post-processing thermal treatments. The morphology and the microstructure of the coatings were observed by SEM and the phase composition was examined by X-ray diffraction. The bioactivity of the coatings was evaluated by soaking the samples in a Simulated Body Fluid (SBF) for 1, 2 and 5 weeks. The bioactive behaviour was then correlated with the thermal treatments and the presence of impurities (in particular Al2O3) in the coatings

Role of process type and process conditions on phase content and physical properties of thermal sprayed TiO2 coatings

Thermal spray represents an advantageous technique for depositing large-area titanium dioxide coat- ings that are of interest for both traditional wear-resistant coatings as well as functional applications such as photo- induced decontamination surfaces. Numerous past studies have examined the phase evolution and properties of TiO2 coatings using different thermal spray processes or parameters. In this paper, an integrated study of thermal sprayed TiO2 was conducted with different thermal spray devices and process parameters for a single feedstock powder comprising the metastable anatase phase. The aforementioned variables are correlated with in-flight par- ticle state (particle temperature and velocity), phase evolution, and coating physical properties. The results are represented through the framework of process maps which connect process parameters with material properties. Based on the phase characterization, an initial exploration of the metastable phase evolution during thermal spray deposition of TiO2 is proposed. Furthermore, the sprayed TiO2 coat- ings show varying degrees of electrical conductivity associated with process-induced stoichiometric changes (vacancy generation) in the TiO2. The effects of these stoichiometric changes as well as extrinsic microstructural attributes (pores, cracks, interfaces), contribute to the complex electrical response of the coatings. This integrated study provides insights into the process–microstructure– property relationship with the ultimate goal of tailoring the functionality of spray deposited oxide thick films

Monitoring and Improving the Reliability of Plasma Spray Processes

Monitoring and improving of process reliability are prevalent issues in thermal spray technology. They are intended to accomplish specific quality characteristics by controlling the process. For this, implicit approaches are in demand to rapidly conclude on relevant coating properties, i.e., they are not directly measured, but it is assumed that the monitored variables are in fact suggestive for them. Such monitoring can be performed in situ (during the running process) instead of measuring coating characteristics explicitly (directly) and ex situ (after the process). Implicit approaches can be based on extrinsic variables (set from outside) as well as on intrinsic parameters (internal, not directly adjustable) having specific advantages and disadvantages, each. In this work, the effects of atmospheric plasma spray process variables are systemized in process schemes. On this basis, different approaches to contribute to improved process reliability are described and assessed paying particular attention to in-flight particle diagnostics. Finally, a new test applying spray bead analysis is introduced and first results are presented