Study On In Situ Laser Synthesizing Ti-Ti_x (B/C/Si)_y Biocoatings On TC4 Alloy

Biocoatings both have the excellent mechanical property of metal materials and biological properties of coatings materials, they were considered to be the most effective way of developing a biomaterial with excellent combinationpreperty. The most researched biocoating materials were ceramics, which compared with mateal materials, have a big gap in coefficient of heat expansion, thus lead to a bad material compatibility with metal materials. Additionally, traditional technology of fabricate coating, the bond way of coatings with abstrat main in mechanical bond. All of above lead to a bad bond strength with abstract and the coatings have the defect of tendency of crack and spalling. All of these indicated that it is difficult to fabricate a biocoating which satisfied with clinical application.In this paper, with the fact that laser alloyed coatings have a strong bonding with abstract and the purpose of developing new biocoatings materials, we raised a idea that fabricated Ti/TiB,Ti/TiC and Ti/Ti-Si composite biocoatings on biomedical TC4 alloy by laser alloyed technology. By optimize the process parameters, the obtained composite coatings have excellent bonding and perfect surface morphology with abstract and without any defect, such as crack, spalling and pore. The microstructures, phase constitutions, formation mechanismof reinforcement, wear resistance, corrosion resistance and biocompatibility by use of scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), friction-wear test, electrochemical corrosion test and cell proliferation test.After laser-boronizing treatment, the Dendritic and cellular TiB reinfore phase was in situ synthesized in the in the laser alloyed coatings. With the concentration of B increased, the content of TiB increased in the alloyed coatings. Because of good thermal conductivity of TiB, the cooling velocity of alloyed coatings was increased, this lead to grain morphology changed from dendrite to cellular crystal and the micro-hardness of laser alloyed coatings increased, When the alloy powder was B, the micro-hardness of alloyed coating is up to 1550HV0.1.After laser melting of Ti-C coatings, the results showed that the reinforced phase TiC primary in the form of dendrite and with little of cellular crystal. With the increase of C in the alloy powder, the absorption efficiency of alloy powder to laser energy, addition of heat release of in situ laser synthesizing reaction, the cooling velocity of alloyed coatings was decreased, this leading to the microstructure of TiB get bigger and well-distributed. Thus, the results of microhardness test show that the 67%C+33%Ti coating has the highest microhardness, but the distribution of microhardness is not so uniformity, the microhardness of C coating is lower than that of 67%C+33%Ti coating, but its hardness distributions uniformity.After laser melting of Ti-Si coatings on biomedical TC4, silicides reinfore phase were in situ synthesized in the in the laser alloyed coatings, when Si in a low content, the primary phase was Ti5Si3, as the content of Si increase to a certain degree, the toughness phase TiSi2 was appeared, our research showed that with the existence of TiSi2, the brittleness could be mend effectively.The results of friction-wear test showed that after laser alloyed with B,C,Si, the friction coefficient of laser alloyed coatings droped obviously and wear resistance increased 4.35 to 28.89 times, the abrasion mechanism of substrat displayed as adhesive wear, alloyed coatings displayed as abrasive wear because of the reinforce phase TiB,TiC and Ti5Si3 exist in the alloyed coatings. The results of electrochemical corrosion test showed that the corrosion of alloyed coatings primary displayed as galvanic corrosion. In the process of corrosion, Ti corrosion prior to TiB,TiC and Ti5Si3, Since the potential of TiB,TiC and Ti5Si3 more positive than substrat. As the content of TiB,TiC and Ti5Si3 increased, the passivation of laser alloyed coatings get not obvious and the corrosion resistance improved. In the process of laser alloy, the cooling velocity was slow in the mediate layer of laser alloyed coatings, the impurities separate out from crystal boundary, in the process of corrosion, the impurities caused micro-cell effects and then leading to the corrosion resistance of some of the alloyed coatings get worse. The results of cell proliferation test showed that the biocompatibilities of fabricated coatings were improved compare to sand blasted samples.