Microstructure And Properties Of Silver-containning Layer Of Biomaterial TitaniΜm Alloy By FSP

In this paper,friction stir processing was used to fabricate silver-containing layer on TC4(Ti-6Al-4V).Microstructure and morphologies of silver-containing layer were observed by optical microscope,SEM and TEM.Mechanical properties including hardness and modulus were tested by microhardness tester and nanoindentation.The results showed the influence of incorporation of silver into the layer,and discussed the formation mechanism of silver phase in the matrix and the strengthening mechanism as.Bioassay was conducted to access the antibacterial property and toxicity.The observation of microstructure showed that when rotating speed was elvated from 300 rpm to 375 rpm,no big difference was seen in the silver distribution and microstructure.But different depth of the groove did affect the structure,it was likely because the high heat-conductivity of silver increasing the heat output of the stir zone.Microstructure of stir zone with groove depth of 1mm was comprised of complete β transformed phase,while stir zone with groove depth of 2mm was featured by equiaxed α grain with a little bit α/β lamella.Macroscopic observation could see that silver only existed near the surface of the plates in the form of strip-shaped agglomeration.The silver-containing layer was gauged at least 500μm.As we observed someplace in magnified images,well-distributed silver nanoparticles could be seen on the matrix,and some of them were located on the boundaries.Silver took on varied morphologies at different depth: within 70μm from the surface,silver nanocrystalline was found for it was where the rotating shoulder directly contacted with the materials and thus most severe deformation happened here,which induced mechanical crystallization.From 70μm to 700μm in depth,there was no nanocrystalline but mostly nanoparticular silver,and others like squeezed silver on the boundary and needle-like silver in the β grains.No silver was found deeper than 700μm.Results of mechanical tests and bioassay indicated that incorporating silver particles into the surface of TC4 by FSP could enhance the local hardness,especially for 375-2(375rpm,2mm groove depth),in which silver was severely agglomerated but hardened most as well.The results of nanoindentation showed that a quantity of nanoparticular silver was ubiquitously located on the matrix and enhanced the local hardness as well,but had little influence on modulus.The antibacterial property was satisfactory after adding silver on the surface.375-1 samples(375rpm,1mm groove depth)also showed good biocompatibility.However,silver content was so high for the 375-2 samples that osteoblasts cells could hardly survive on its surface.And thus we must strictly control the content of silver nanoparticles and employed the shallow grooves on the plates.