Effect of Ag alloying and trace precipitation on corrosion resistance of Ti-Ta-Ag ternary alloy.

This work systematically analysed the electrochemical and corrosion behaviour of Ti-Ta-Ag ternary alloy samples in Hank's solution. For the samples with 1.5% and 3% Ag content, the sintering temperature increased from 750 to 950°C, and the corresponding corrosion resistance increased by 100 times due to the increased alloying of Ag; meanwhile for the sample with 4.5% Ag content, the sintering temperature increased from 750 to 950°C, and the corresponding corrosion resistance decreased by six times due to the increased precipitation of Ag. These tests prove that the Ag alloying is beneficial to the enhancement of the corrosion resistance of Ti-Ta-Ag ternary alloy, but the Ag trace precipitation has the opposite effect. A series of electrochemical characterizations and density functional theory calculations explain the mechanism of the above phenomenon. Ag alloying can promote the formation of uniform, complete, dense, stable and thick passivation layer on the surface of Ti-Ta-Ag ternary alloy, which makes Ti-Ta-Ag ternary alloy uniformly corroded without pitting. In addition, Ag alloying can effectively reduce the contact resistance of the solid-liquid interface. However, the trace precipitation of Ag plays the opposite role to the above effect.

Study of Ag precipitation and mechanical properties of Ti-Ta-Ag ternary alloy.

Ti-25Ta-xAg alloy samples with different content of Ag were prepared by spark plasma sintering method. X-ray diffraction, microscopic metallographic, scanning electron microscopy, and transmission electron microscopy were used to analyze the phase structure and morphology of the alloy samples. Ti-Ta-Ag can form a stable ternary alloy system. Furthermore, with the increase of Ag content and sintering temperature, Ag will be precipitated at the grain boundary. In order to explore the precipitation mechanism of Ag in the alloy and its influence on the mechanical properties, the crystal structure, electronic structure, and elastic constant under different Ag solid solubility were calculated systematically by using first-principles calculations. The results show that the critical temperature of Ag in Ti-Ta-Ag ternary alloy is about 2200 K, and the high temperature is favorable for the aging precipitation of Ag. The lattice constants and mechanical properties of (Ti1-x Ag x )3Ta solid solution suddenly change when the Ag solid solubility x value is equal to 0.8, and their changes will follow different rules. The internal mechanism of this phenomenon is that the 4d10 electronic states of Ag have changed from obvious local electronic states to mixed local and non-local electronic states. These results provide theoretical guidance for the application of Ti-Ta-Ag ternary alloys in biomedicine.