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Plasma-sprayed hydroxyapatite (HAp) coatings are widely used to enhance the bioactivity and osseointegration of metallic implants however, their long-term performance under cyclic loading in physiological environments remains a critical concern [1]. In this study, HAp coatings were deposited via plasma spraying [2] onto cylindrical rod Ti64 substrates (5 mm diameter) and subjected to controlled fatigue loading in simulated body fluid (SBF) at 37 °C to replicate in vivo conditions [3]. The samples were exposed to 150 × 10³, 500 × 10³, and 750 × 10³ fatigue cycles to evaluate the progressive effects of mechanical degradation.
The structural and microstructural evolution of the coatings was systematically investigated. X-ray diffraction (XRD) was employed for phase identification and residual stress analysis, revealing changes in crystallinity and stress state with increasing fatigue exposure. Scanning electron microscopy (SEM), coupled with energy-dispersive spectroscopy (EDS), was used to assess surface morphology and elemental composition, highlighting fatigue-induced microcracking, splat delamination, and localized compositional variations. Furthermore, micro-computed tomography (MicroCT) provided three-dimensional characterization of internal porosity, enabling quantification of pore distribution and its evolution under cyclic loading.
The results demonstrate that increasing fatigue cycles lead to progressive microstructural degradation, including crack initiation and propagation, as well as changes in residual stress and porosity distribution. These findings provide important insights into the durability and failure mechanisms of plasma-sprayed HA coatings under physiologically relevant conditions.
[1] Sun, L., Berndt, C. C., Gross, K. A., & Kucuk, A, ‘Material fundamentals and clinical performance of plasma-sprayed hydroxyapatite coatings: A review ’, J. Biomed. Mater. Res., vol. 58, no. 5, pp. 570–592, 2001.
[2] R. B. Heimann, ‘Thermal spraying of biomaterials’, Surf. Coat. Technol., vol. 201, no. 5, pp. 2012–2019, 2006, doi: https://doi.org/10.1016/j.surfcoat.2006.04.052.
[3] H. M. Kim, T. Miyazaki, T. Kokubo, and T. Nakamura, ‘Revised simulated body fluid’, in Key Engineering Materials, Trans Tech Publ, 2001, pp. 47–50.
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