Laser Induced Porosity and Crystallinity Modification of a Bioactive Glass Coating on Titanium Substrates

Functionally graded bioactive glass coatings on bioinert metallic substrates were produced by using continuous-wave (CW) laser irradiation. The aim is to achieve strong adhesion on the substrates and high bioactivity on the top surface of a coating material for load-bearing implants in biomedical applications. The morphology and microstructure of the bioactive glass from the laser coating process were investigated as functions of processing parameters. Laser sintering mechanisms were discussed with respect to the resulting morphology and microstructure. It has been shown that double layer laser coating results in a dense bond coat layer and a porous top coat layer with lower degree of crystallinity than an enameling coating sample. The dense bond coat strongly attached to the titanium substrate with a 10 mu m wide mixed interfacial layer. A highly bioactive porous structure of the top coat layer is beneficial for early formation of a bone-bonding hydroxycarbonate apatite (HCA) layer. The numerical model developed in this work also allows for prediction of porosity and crystallinity in top coat layers of bioactive glass developed through laser induced sintering and crystallization.