Study On The Process And Properties Of TC4 Titanium Alloy Surface By Molten Salt Electrolytic Boriding

With the purpose of improving the hardness of the TC4 titanium alloy, used a system of FClNaK-Na2B4O7, boronized layer was prepared on TC4 titanium alloy by electrolysis in molten salt.Chose the molten salt of NaCl-KCl-NaF-Na2B4O7 mole ratio 2:2:1:0.04 for molten salt electrolysis boronizing on the sample surface. The effects of current density, duty cycle, electrolytic time and electrolytic temperature on deposition rate, thickness,composition, morphology and phase were studied by weight increase method, GDS, SEM and XRD. Used micro hardness tester and electrochemical workstation to measure the hardness and corrosion resistance. At the same time, studied the boronizing process from the perspective of thermodynamics and kinetics.The results showed that as electrolytic temperature and time increased, deposition rate increased, so did the boronized layer; as current density increased, deposition rate first increased then decreased, so did the boronized layer, thickness and deposition rate reached the maximum when the current density was 60mA/cm2; as duty cycle increased, deposition rate decreased, duty cycle had no effect on thickness. The boronized layer did not contain Al, and the V easily dissolved in the borides. As electrolytic temperature, electrolytic time and duty cycle increased, the surface grain size of the boronized layer became thick and big; as current density increased, the surface grain size of the boronized layer became tiny; alloy layer was not formed on the surface of the substrate when the electrolytic time was 30 min. The boronized layer consists of TiB and TiB2 with( 111) preferred orientation. The TiB phase diffraction peaks of the boronized layer shifted to high angle for smaller atomic radius V element solid solution in larger atomic radius of Ti. Optimal process parameters of molten salt electrolytic boriding: current density 60 m A/cm2, duty cycle 20%, electrolysis time 90 min, electrolysis temperature 840℃, electrolysis cycle1000 s. Hardness and corrosion resistance of matrix were improved after boriding.Reactions of The boronizing process, Ti+2B=TiB2 was preferred; as temperature increased,the diffusion coefficient of boron in TC4 titanium alloy increased, diffusion activation energy was about 68.1KJ/mol.