Development of Hydrothermally Synthesized Hydroxyapatite Coatings on Metallic Substrates and Weibull's Reliability Analysis of its Shear Strength

Hydroxyapatite (HA) and Mg-substituted HA coatings were synthesized on Mg-9Al-1Zn and Ti-6Al-4V by the hydrothermal process. Grazing-incidence X-ray diffractograms showed the formation of calcium–magnesium–phosphate is resulted from the substitution of Mg2+-ions into HA crystal. The chemical state of Mg2+-ions in Mg-substituted HA coatings was examined by X-ray photoelectron spectroscopy. The shear test results showed the Mg-substituted HA coatings deposited on Mg-9Al-1Zn have higher shear strength than those coatings on Ti-6Al-4V. The Weibull model provided a powerful statistical method for assessing failure mechanism of hydrothermal coatings, which is attributed to a wear-out failure model with a Weibull modulus m > 3.