Carbon nanotube (CNT) reinforced hydroxyapatite composite coatings have been successfully fabricated by laser surface alloying. The phase compositions and the microstructure of the composite coatings were studied using X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). TEM observation showed that a large amount of CNTs can be found with their original tubular morphology in the composite coatings, even though some CNTs react with titanium element in the substrate during laser irradiation. Additionally, measurement on the elastic modulus, hardness of the composite coatings by nanoindentation tests indicated that the mechanical properties are affected by the amount of CNTs in the starting precursor materials. Therefore, CNT reinforced hydroxyapatite composite coating is a promising coating material for high-load-bearing metal implants.
Multi-walled carbon nanotubes (CNTs) have been successfully introduced into hydroxyapatite (HA) coatings using laser surface alloying. It is evident from transmission electron microscopy (TEM) observations that the CNTs present in the matrix still keep their multi-walled cylinder graphic structure, although they undergo the laser irradiation. Scratching test results indicated that the as-alloyed HA composite coatings exhibit improved wear resistance and lower friction coefficient with increasing the amount of CNTs in the precursor material powders. These composites have potential applications in the field of coating materials for metal implants under highload-bearing conditions.
Nanoindentation and nanoscratch tests were performed for diamond-like carbon (DLC) coatings on the different steel substrates in order to investigate the deformation and failure behaviors of the coating/substrate systems and their tribological properties. In this work, DLC coatings with a thickness of approximate 500 nm were grown on 9Cr18 and 40CrNiMo steel substrates by vacuum magnetic-filtering arc plasma deposition, respectively. The nanoindentation results show that the indentation response was plasticity-dominated. The peak load on sample, residual indentation depth, hardness, modulus can provide important information of the mechanical resistance of the materials tested. The scratch process with the ramping normal load was analyzed into the three regimes, which are fully elastic recovery, plastic deformation and delamination of coatings. This shows that the scratch response was controlled by plastic deformation in the substrate. The substrate plays an important role in determining the mechanical properties and wear resistance of such coatings. As a consequence, 9Cr18 steel is a better candidate of substrate materials for DLC coatings due to the better load-carrying capacity and scratch/wear resistance of DLC/9Cr18.
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