Comparative investigation into effects of ZrO2 and Al2O3 addition in fluorapatite laser-clad composite coatings on Ti6Al4V alloy

Composite coatings consisting of fluorapatite mixed with 20 wt% yttria (3 mol%) stabilized cubic phase zirconia (c-ZrO 2 , 3Y-TZP) or 20 wt% alumina (α-Al 2 O 3 ) were deposited on Ti6Al4V substrates using a Nd:YAG laser cladding system. The interface morphology, phase composition, micro-hardness and biological properties of the two coatings were examined and compared. The results showed that the fluorapatite/Al 2 O 3 specimen underwent a greater inter-diffusion at the interface between the coating layer and the transition layer than the fluorapatite/ZrO 2 specimen. During the cladding process, the ZrO 2 and Al 2 O 3 components of the coating were completely decomposed or underwent phase transformation. In addition, the fluorapatite was partially decomposed. For both specimens, the coating layers contained fluorapatite, CaF 2 and CaTiO 3 phases. The coating layer of the fluorapatite/ZrO 2 specimen additionally contained TTCP, CaO, CaZrO 3 and m-ZrO 2 (monoclinic phase), while that of the fluorapatite/Al 2 O 3 specimen contained β-TCP, CaAl 2 O 4 and θ-Al 2 O 3 . The average micro-hardness of the fluorapatite/ZrO 2 coating layer (1300 HV) was approximately 200 HV higher than that of the fluorapatite/Al 2 O 3 coating layer (1100 HV). Both specimens generated dense bone-like apatite following immersion in simulated body fluid for 3 days. In other words, both specimens had a good in vitro bioactivity. However, the fluorapatite/ZrO 2 specimen showed a better initial attachment and spread of osteoblast-like osteosarcoma MG63 cells than the fluorapatite/Al 2 O 3 specimen in in vitro biocompatibility tests performed for 24 h.