Laser Cladding MgO/HA Coating And Investigation On Its Properties

Ti-6Al-4V alloy is a kind of common used biomaterial. It is often used as bone nail, blade plate, and other bony replacement tissue. However, titanium alloy belong to bio-inert materials, which limited its usage. In order to improve its bioactivity and corrosion resistance, MgO substituted HA coating was obtained via laser cladding technology.Firstly, laser technology was investigated systematically to decide a proper technology for obtaining an excellent coating. The results showed that the proper technology parameters are as following:the electrical current of 80 A, the pulse width of 2.0 ms, the pulse duration of 20 Hz, laser scanning speed of 500 mm/min, laser scanning space of 0.4 mm, and the defocus value in the range of 25 mm to 30 mm. The influences of MgO content on the phase distribution, morphology, and microstructure of the coatings were investigated. The results revealed that the main phases consisted of Ca3HP4O14?Mg3(PO4)2?Ca3Mg3(PO4)4?MgO? CaTiO3 and TiOx. The relative amount of the phases varied with varying MgO content. With increasing of MgO content, the relative amount of CaTiO3 increased first and then decreased, that of Mg3(PO4)2 always increased, while that of Ca3Mg3(PO4)4 decreased, and that of Ca3HP4O14 remained the same. The average grain size decreased with increasing of MgO content from 16.71 Wt.% to 37.57 Wt.%, and remained the same after the content of MgO was over 37.57 Wt.%.The surface of the coating which consisted of MgO content less than 37.57 Wt.% presented a smoother morphology. After the content of MgO is over 37.57 Wt.%, the surface became rougher and rougher. The surface roughness of the sample is about 39.85?m. OM investigation results showed that an excellent metallurgical bonding between the coating and the substrate was obtained. The microhardness in the coating increased first and then decreased with increasing of the MgO content and got a maximum value of 1082 HV0.2 at the content of MgO of 44.52 Wt.%.The wettability of MgO/HA coatings were investigated. The calculation results of surface free energy (SFE) indicated that the SFE decreased with increasing MgO content, indicating that a higher content of MgO does no benefit for improving wettability. The maximum SFE of 62.9 mJ/m2 was obtained at the content of MgO of 16.71 Wt.%, indicating this coating owns a better wettability. The contact angle measurements between the coatings and the SBF solution gave a further proof to assist the above conclusion.The in vitro bioactivity of the samples was carried out by SBF immersion tests. XRD results showed that the peaks corresponding to CaP were observed for all the MgO substituted samples after immersed in SBF for 6 days. Furthermore, the relative peak intensity of CaP phase increased first and then decreased with increasing of MgO content, and got a maximum value when the MgO content was up to 28.67 Wt.%. This indicated that the proper substitution of MgO is benefit for the deposition of CaP phase in the SBF solution. The UV-vis results further indicated that the deposition layer consisted of small amount of OH" group but much of PO43- group. The morphology of the immersed sample can be characterized as dense graphical particle. EDS results revealed that the ratio of Ca to P decreased with increasing MgO content.Corrosion resistance of the coated samples in SBF solution was investigated by electrochemical corrosion tests. It indicated that the corrosion potential of the coatings decreased with increasing MgO content, while the corrosion current increased first and then decreased. It was concluded that the coating substituted by MgO with the content of 16.71 Wt.% possessed a more excellent corrosion resistance.All in all, the coating with a proper substitution of MgO presents a desirable wettability, an excellent ability for CaP deposition, and an improvement of the corrosion resistance in SBF solution.