Progress on the laser-surface-alloyed carbon-nanotube reinforced hydroxyapatite bioactive composite coating
Carbon nanotubes (CNTs) have been attractive candidates for fundamental research studies since their discovery by Iijima. Several applications were proposed for CNTs many of which are concerned with conductive or high strength composites, in which the inclusion of CNTs in a ceramic matrix is expected to produce composites possessing high stiffness and improved mechanical properties compared to the single-phase ceramic material, because CNTs exhibit excellent mechanical properties and high thermal stability.
Under the financial support of the National Natural Science Foundation of China (Grant No.50471088) and China Postdoctoral Science Foundation (Grant No.2004035073), Dr. Chen Yao, a postdoctor in Institute of Mechanics, Chinese Academy of Sciences, successfully fabricated high-quality carbon nanotube (CNT) reinforced hydroxyapatite composite coatings deposited on the surface of Ti-6Al-4V substrate using laser surface alloying. TEM and HRTEM 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. Furthermore, nanoindentation technique is employed to study the variation of the mechanical properties of laser surface alloyed coatings with different CNT content. It showed that the addition of CNTs has notable effect on the value of hardness of these composite coatings, but has not strong effect on the value of modulus of these as-alloyed coating, which is beneficial to decrease the mismatch of the modulus between the as-alloyed coating and living bone tissues. The reason for this phenomenon results from either the combination-strengthening role of the residual CNTs and the in-situ formation of TiC in the hydroxyapatite matrix, and the notable decrease in the value of modulus of multi-walled carbon nanotubes usually having structural defects.
Abovementioned experimental results strongly illustrate that the remarkable increase in the hardness and slightly increase in the modulus of the CNT reinforced hydroxyapatite coating has a potential contribution toward improving both the bone repair and high-load-bearing implants.
A series of research papers on the Laser-suface-alloyed CNT reinforced hydroxyapatite coating have been published in the Applied Physics Letters (2005,Vol.86，Article No. 251905) and Carbon ( in press).