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Abstract:The microstructural evolution and tensile properties of Ti-3Al-8V-6Cr-4Mo-4Zr titanium alloys with various Si contents were investigated. The results revealed that the addition of trace Si and the presence of Zr induced the formation of (TiZr) 6 Si 3 silicides, in the size range from 100 nm to 300 nm. The fine silicide precipitates refined β grains. The tensile strength increased about 40 MPa due to precipitation strengthening and grain refinement, and the ductility of the two alloys was similar. The tensile fracture mode of the alloys was dimple ductile fracture.

Micro-arc oxidation (MAO) coatings with 2 μm, 5 μm and 10 μm in thickness were produced on Ti-6Al-4V titanium alloy by MAO treatment, and the effect of coating thickness on the high cycle fatigue property was investigated. The microscopies and phases of coatings were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The results indicated that the coatings were mainly composed of anatase TiO2. The MAO process generated micro pits at the substrate surface. The micro pits played a role of the notches, which induced the crack initiation during fatigue loading. The fatigue life of samples decreased with the increase of coating thickness. The micro pits were the main factor for the decrease of the fatigue life.