In this work,the microstructure of titania coating fabricated on the surface of hydrostatically extruded titanium grade 4 with the use of the micro-arc oxidation method was studied.The surface topography and microstructure investigations performed with atomic force microscopy and scanning and transmis-sion electron microscopy revealed that,by using an Na2HPO4 electrolyte,a well-adherent porous coating is produced on the top surface and side walls of the extruded rod.The distribution of chemical elements was analyzed by using energy dispersive X-ray spectroscopy.The chemical elements dissolved in the elec-trolyte(Na,P and O)incorporated into the coating.Sodium locates preferentially in the outer part of the coating,while phosphorus and oxygen are distributed throughout the whole coating.The most relevant finding shows that a grain refinement caused by a hydrostatic extrusion provoked an increase in density of high-angle grain boundaries(HAGB),which in turn secured the formation of a continuous amorphous layer close to the substrate.The presence of this layer compensates for the effect of anisotropic substrate,producing a comparable and homogenous microstructure with a large number of micropores.

?.Maj;D.Wojtas;A.Jarz?bska;M.Bieda;K.Trembecka-Wójciga;R.Chulist;W.Kozio?;A.Góral;A.Trelka;K.Janus;J.Kawa?ko;M.Kulczyk;F.Muhaffel;H.?imeno?lu;K.Sztwiertnia

Institute of Metallurgy and Materials Science,Polish Academy of Sciences,Reymonta 25,Krakow 30-059,Poland;Faculty of Physics and Applied Computer Science,AGH University of Science and Technology,Krakow,Poland;Academic Centre of Materials and Nanotechnology,AGH University of Science and Technology,Krakow,Poland;Institute of High Pressure Physics,Polish Academy of Sciences,Warsaw,Poland;Department of Metallurgical and Materials Engineering,Istanbul Technical University,Istanbul,Turkey

材料科学技术（英文版）

[1]?.Maj;D.Wojtas;A.Jarz?bska;M.Bieda;K.Trembecka-Wójciga;R.Chulist;W.Kozio?;A.Góral;A.Trelka;K.Janus;J.Kawa?ko;M.Kulczyk;F.Muhaffel;H.?imeno?lu;K.Sztwiertnia-.Titania coating formation on hydrostatically extruded pure titanium by micro-arc oxidation method)[J].材料科学技术（英文版）,2022(16):224-235

Titania,HAGB

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