Residual Stresses in Plasma-Sprayed Hydroxyapatite Coatings

Residual Stresses in Plasma-Sprayed Hydroxyapatite Coatings 7.6.6.1 Stress Analysis by X-ray Diffraction 

Measurements of residual stress and strain, Young s modulus and adhesive bonding strength of the hydroxyapatite coating after immersion in HBSS showed 

Topic et al. (2006) showed that the curvature increased for all as-sprayed and grit-blasted samples as well as for samples incubated up to 28 days whereas incubation for 56 days caused a significant decrease in the radius of curvature, R. Accordingly, a compressive residual stress was induced in the uncoated, grit-blasted Ti6Al4V samples, the as-sprayed HAp coatings and all incubated coatings with the exception of the samples incubated for 28 days (Fig. 7.50). 

Hence in coatings incubated for only up to 28 days the newly formed layer of secondary hydroxyapatite is decoupled from the stress state of the original layer showing essentially zero stress. Increasing the incubation time may also increase the compressive stress state again caused by reorganisation, consolidation and densification of the biomimetically precipitated Ca-deficient bone-like apatite layer (Gotze etal., 2001). 

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Sergo, V., Sbaizero, O., and Clarke, D.R. (1997) Mechanical and chemical consequences of the residual stresses in plasma sprayed hydroxyapatite coatings. Biomaterials, 18 (6), 477-482. 

Yang, Y.C. and Chang, E. (2005) Measurement of residual stresses in plasma-sprayed hydroxyapatite coatings on titanium alloy. Surf. Coat. Technol., 190... 

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