Production and characteristics of tissue-reinforced ha coats on magnesium with thermal spraying techniques

Magnesium and its alloys are potential biodegradable implant materials due to their attractive biological and mechanical properties. But their poor corrosion resistance may result in sudden failure of the implants. In order to increase corrosion resistance and bone bioactivity of magnesium implant materials, hydroxyapatite (HA: Ca10(PO4)2(OH)6) is often coated on their surface so that real bond with surrounding bone tissue can be formed. In present study, HA and HA+ 10, 20, 30 % wt. TiSZ reinforced coatings were deposited on magnesium substrate as a single and double layer using thermal spray processes. Bioceramic HA and HA+TiSZ coatings were fabricated by plasma spray. Ti buffer layer was produce by high velocity oxy-fuel technique for double layer coatings The coated specimens were characterized by X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (SEM, EDS). The corrosion behaviors in simulated body fluid (SBF) of coatings were investigated by electrochemical corrosion test. Rockwell-C adhesion and scratch test were performed in order to determine adhesion and cohesion properties of the coatings. Microscopic observation show that, dense, continious Ti buffer layer and bioceramic HA, HA+TiSZ coatings were produced successfully. Bioceramic top layer have been traditional plasma sprayed HA microstructure with the micro porous and lamellar structure. In addition, the continuous adhesion between the coating layers and the substrate is obtained. XRD analysis reveal that phase structure of HA coatings is pure HA. Also, TiSZ tetragonal ZrO2 peaks are observed for HA+TiSZ composite coatings. According to corrosion test results, pure hydroxyapatite coating provides excellent corrosion resistance compared to HA+TiSZ composite coatings. In addition, the double layer HA-Ti coating on magnesium substrate is more resistant to corrosion than single layer HA coating. There is no observed phase transformation and microstructural deformation after corrosion tests. Rockwell-C adhesion tests show that adhesion of coatings improve with the addition of TiSZ and Ti buffer layer application. Also, Scratch test results indicate that TiSZ addition is not improved scratch behavior of the coatings.