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Effect of pulse laser treatment at different process variables on mechanical behavior of carbon nanotubes electrophoretically deposited on titanium alloy

Majkowska-Marzec Beata, Staszewski Kacper, Sypniewska Joanna

Acta of Bioengineering and Biomechanics

2023

Vol. 25, no. 2

157--168

Titanium and its alloys are widely used as biomaterials for long-term implants, but they are usually surface-modified due to their weak bioactivity and wear resistance. Laser processing was used to modify the surface layer, and elemental carbon was a component of the deposited coatings. This research aims to use a combination of both methods based on preliminary electrophoretic deposition of multi-wall carbon nanotubes (MWNCTs) followed by pulse laser treatment. Carbon nanotubes were chosen due to their mechanical and chemical stability as well as their tubular shape, resulting in enhanced mechanical properties of laser-modified layers. Methods: The pulse laser power and laser scanning speed were defined as variable process parameters. The microstructure, roughness Ra, nanohardness H, Young’s modulus E, and indent depth values were measured, and the H/E, H 3 /E2 , and relative changes of all these values in comparison to MWCNTs-coated and non-coated surfaces, were calculated. Results: The obtained results show that the best mechanical properties of MWCNTs-coated and laser-treated specimens are obtained at a laser power of 900 W and laser feed of 6 mm/s. The observed relations can be explained considering processes occurring on the surface such as deposition of carbon nanotubes, melting and re-crystallization of the surface layer, formation and possible partial decomposition of titanium carbides, and associated changes in local chemical composition, phase composition, and a level of residual stresses beneath the surface. Conclusions: The developed process can substitute the time and money-consuming carbonization of titanium and its alloys.

Microstructure and mechanical properties of laser surface-treated Ti13Nb13Zr alloy with MWCNTs coatings

Majkowska-Marzec Beata, Sypniewska Joanna

Advances in Materials Science

2021

Vol. 21, nr 4(70)

5--18

Laser surface modification of titanium alloys is one of the main methods of improving the properties of titanium alloys used in implantology. This study investigates the microstructural morphology of a laser-modified surface layer on a Ti13Nb13Zr alloy with and without a carbon nanotube coating deposited by electrophoretic deposition. Laser modification was performed for samples with and without carbon nanotube coating for two different laser powers of 800 W and 900 W and for different scan rates: 3 mm/s or 6 mm/s at 25 Hz, and the pulse duration was 2.25 ms or 3.25 ms. A scanning electron microscope SEM was used to evaluate the surface structure of the modified samples. To observe the heat-affected zones of the individual samples, metallographic samples were taken and observed under an optical microscope. Surface wettability tests were performed using a goniometer. A surface roughness test using a profilograph and a nanoindentation test by NanoTest™ Vantage was also performed. Observations of the microstructure allowed to state that for higher laser powers the surfaces of the samples are more homogeneous without defects, while for lower laser powers the path of the laser beam is clearer and more regular. Examination of the microstructure of the cross-sections indicated that the samples on which the carbon nanotube coating was deposited are characterized by a wider heat affected zone, and for the samples modified at 800 W and a feed rate of 3 mm/s the widest heat affected zone is observed. The wettability tests revealed that all the samples exhibit hydrophilic surfaces and the samples with deposited carbon nanotube coating increase it further. Surface roughness testing showed a significant increase in Ra for the laser-modified samples, and the presence of carbon nanotubes further increased this value. Nanoindentation studies showed that the laser modification and the presence of carbon coating improved the mechanical properties of the samples due to their strength.