Microstructural investigation of porous titanium coatings, produced by thermal spraying techniques, using plasma atomization and hydride-dehydride powders, for orthopedic implants

Abstract

The present study focuses on porous titanium (commercially pure Ti) coatings for future use on medical implants, manufactured by specific thermal spray method. Its objective is to investigate the possibility of Ti porosity to offer room for medication storage in addition to bone growth promotion. Three specimens for each different type of coating were produced by different sets of thermal spray process/feedstock powder, namely, (1) Flame Spray (FS) with spherical Plasma Atomization (PA) powder, (2) Atmospheric Plasma Spray (APS) with spherical PA powder and (3) APS with angular Hydride – Dehydride (HDH) powder. The specific types of specimens along with the two powders produced by the PA and HDH processes were characterized using various techniques, namely (a) Roughness measurements of the coated surfaces and thickness measurements of the coatings, which disclosed the highest values for the FS-PA coating, Ra = 11.19 ± 0.21 μm and average thickness of 281 μm, (b) Optical microscopy and SEM-EDS to study the surface morphology and microstructure of the coatings and discover any possible oxidation or other phases. The porosity percentage was measured and the pore size distribution was also estimated. The porosity percentages of the coatings ranged from 12% on the APS-PA coating to 34% on the FS-PA coating, (c) XRD analyses which showed varying titanium oxide formations for each type of specimen. These oxides may prove to be beneficial for the development of osseous tissue, (d) assessment of biological response of the coatings in vitro that resulted in satisfactory primary response in a physiological environment and the formation of calcium phosphate phases with Ca/P ratio of 1.61 and (e) Vickers microhardness measurements, which resulted in values that fluctuated from 786.6 for the FS-PA coating to 967.6 for the APS-HDH coating. Overall, the produced FS-PA coating is characterized by high porosity content and satisfactory bioactivity, in order to fulfill the objective of the project for biomolecule incorporation and drug storage.