Residual stress in plasma-sprayed hydroxyapatite coating measured by the material removal method

摘要

Plasma-sprayed hydroxyapatite on titanium alloy implants is being used for orthopedics and dentistry [1,2]. The HA coating is able to form a chemical bond to bone [3,4]. Data from a canine transcortical plug pushout study have confirmed the superior shear strength of a 50μm thick coating when compared to a 200μm coating [5]. It has been suggested that the residual stress might have been involved in the phenomenon [6]. Recently Millet et al. used the X-ray diffractometry to study the residual stress of HA coating on titanium alloy and found that the stress was compressive [7]. The residual stress state in the coating does explain the findings that the bonding strength of the system decreases with increasing compressive residual stress, which has been supported by mechanics of coated surfaces [8.9]. The X-ray diffractometry for stress analysis is a nondestructive and widely accepted method in this regard. Unfortunately the use of this technique is limited by the shallow penetration on the X-ray beam and therefore only the surface residual stress at 10-50μm depth can be obtained [10], the penetration depth of X-ray varying with the materials. Hence the residual stress state at the more crucial HA/metal interface cannot be obtained.