Residual stress analysis in implant coatings using X-ray and neutron diffraction techniques

Abstract

During clinical use of an implant, the mechanical stresses are added to preexisting residual stresses. The magnitude of these stresses affects the hydroxyapatite coating's performance. We intended to study in this work, by neutron diffraction and conventional X-ray diffraction methods, the macrostresses induced by a plasma-spraying process in the coating and at the interface. Neutron diffraction is a suitable technique to study the strain distribution in a bulk material. X-ray diffraction has been used to determine residual stress in the hydroxyapatite coating. Using neutron diffraction method, we calculate the stress on the titanium alloy but see no real difference between the stress on the coated and the non-coated samples. With X-ray diffraction method, it appears that the stress level is compressive on every sample.

The major interest of neutron diffraction method is that measurements can be done on a thick coating, in a non-destructive way with the disadvantage of a large gauge volume that we had to use. Polishing is necessary for measurements inside the material when using X-ray method. This destructive method may alter the stress field of the deposit.

Key Words:

• Implant
• Hydoxyapatite coatings
• Stress
• Strain
• Neutron diffraction
• X-ray diffraction