Laser cladding of HA/Ti composite coating on NiTi alloy

Abstract

To accelerate the bone growth around a metallic implant and to achieve the mechanical characteristics needed for biomedical applications, a hydroxyapatite/pure titanium (HA/Ti) composite coating was produced on NiTi alloy substrate by laser cladding. The experimental results showed that an excellent metallurgical bonding between the coating and the substrate was obtained. Owing to decomposition of HA under irradiation of high power laser, the microstructures of coating were mainly composed of CaO, CaTiO 3 , titanium phosphide and HA phases. In vitro experimental result demonstrated that HA/Ti composite coating made the bioactivity of NiTi alloy improved remarkably while restraining Ni ion from releasing.

Research Progress Regarding Interfacial Characteristics and the Strengthening Mechanisms of Titanium Alloy/Hydroxyapatite Composites

“…Recently, there have been two research methods that have been used on Titanium alloy/Hydroxyapatite composites: (1) Various coatings such as Hydroxyapatite, HA-Ti(C,N)-TiO 2 , HA-Ti, graphene-HA, etc. are coated on Titanium or Titanium alloy substrates using sol-gel method, laser cladding method, plasma spray method, plasma electrolytic oxidation, micro-arc oxidation method, and other methods [ 11 , 14 , 15 , 17 , 40 , 43 , 44 , 45 ]. Figure 1 shows the morphology and schematic view of Plasma electrolytic oxidation (PEO) method.…”

“…The oxygen originated from water vapor, which was from electrolyte and decomposition reaction of HA [ 40 ]. In HA/Ti composite coating prepared by laser cladding, it was found that decomposition products of HA floated into upper layer [ 17 ], so that a clear interface between alloy area and coating would appear [ 17 ]. Besides, phosphorus resulting from decomposition reaction of HA reacted with Titanium and formed Titanium phosphorus compound, which could have been reserved in the alloy area, but calcium-phosphate compound floated into upper coating layer [ 17 ].…”

“…In HA/Ti composite coating prepared by laser cladding, it was found that decomposition products of HA floated into upper layer [ 17 ], so that a clear interface between alloy area and coating would appear [ 17 ]. Besides, phosphorus resulting from decomposition reaction of HA reacted with Titanium and formed Titanium phosphorus compound, which could have been reserved in the alloy area, but calcium-phosphate compound floated into upper coating layer [ 17 ]. In graphene-HA composite coatings using electrochemical deposition method, it was found there is the existence of TiC produced by the reaction between graphene and Titanium, which resulted in the reaction bonding between Titanium and coating [ 46 ].…”

“…Similar conclusions are reported elsewhere [ 16 ]. Yang et al found a thick apatite layer on the surface of coated HA/Ti composite compared with substrate alloy, suggesting the improvement of bioactivity [ 17 ].…”

“…However, there are some main defects concerning the interface between the substrate and the coating in the coated materials, such as lower fracture toughness of HA, interface cracks in the deposition process, low interface adhesion at the interface between metal substrate and the ceramic, and uneven thickness distribution [ 9 , 13 , 14 , 17 , 18 ]. As an example, triclinic apatite coating on the Titanium substrate prepared by chemical deposition gradually occurred during plastic deformation, which separated from the matrix when a load was continuously improved.…”