Titanium alloy has low hardness and poor wear resistance. When it is used as propeller blades, turbine blades, turbines, tail pipes, pumps, valves and other flow components, it is easy to cause cavitation erosion in the components due to the pressure change area in the fluid. When the cavitation bubble collapses near the solid boundary, the surface of the solid material will peel off, which will reduce the equipment performance, shorten the service life, and even lead to the failure of titanium alloy members. Over the years, new research progress has been made on the protection measures of titanium alloy cavitation damage at home and abroad. The following will be discussed in detail from three aspects: heat treatment of the whole material, surface treatment and adding corrosion inhibitor to fluid medium.
1,Heat treatment
The results show that heat treatment can improve the cavitation resistance of titanium alloy by changing its microstructure. Li Haibin heat treated Ti6Al4V alloy at different temperatures (1020 ℃, 950 ℃, 850 ℃) to obtain the weidler microstructure, two-state microstructure and equiaxed microstructure. After 8 h cavitation test in deionized water, the author found that the cumulative weight loss of all the heat treated samples was less than that of the original Ti6Al4V. Among them, the weidler sample treated by 1020 ℃+ water quenching has the lowest cavitation erosion weight loss (77.9% of the original sample) and the highest cavitation erosion resistance coefficient (1.83 times of the original sample). The results show that the cavitation resistance of Ti6Al4V alloy with different microstructure is also different. The fracture toughness and tensile strength of Ti6Al4V are enhanced by the martensite α 'phase or flake α phase in the weisenberg structure, and the energy of absorbing cavitation collapse is enhanced. The primary α phase in the two-state structure has a strong work hardening ability, while the β transformation structure (secondary α phase) can improve the strength and hardness of the material, and also enhance the energy of Ti6Al4V to absorb the collapse of cavitation. The equiaxed structure also contains secondary α phase, but its content is less, so the improvement of cavitation erosion resistance is not as obvious as that of the two-state structure. In this experiment, the cavitation erosion resistance of the weidler structure is the best, followed by the two-state structure, and the equiaxed structure is the lowest.
2,Surface treatment
As cavitation erosion starts from the surface of the material, surface treatment of titanium alloy naturally becomes an effective measure to improve its cavitation erosion resistance. So far, the surface treatment techniques used to improve the cavitation resistance of titanium alloys at home and abroad include laser texturing, laser gas nitriding, chemical heat treatment, ion implantation, hot dip plating and so on, and some achievements have been achieved.
3,Add corrosion inhibitor
Cavitation damage of titanium alloys in corrosive environment usually involves the synergistic effect of corrosion damage. Therefore, adding corrosion inhibitor can be regarded as an effective way to improve the cavitation resistance of titanium alloys. The cavitation damage behavior of Ti6Al4V alloy in 55% (mass fraction) LiBr solution +1% anodic corrosion inhibitor NaNO2 was investigated. The results show that after hollowing for 1 h in LiBr solution containing corrosion inhibitor, the surface voids are significantly reduced compared with the surface without corrosion inhibitor. After 8 h, the cumulative weight loss was 90.5% without corrosion inhibitor. The NO2- generated by the addition of this corrosion inhibitor will be adsorbed into the voids with strong activity on the surface of passivated film, which makes the passivated film more easily generated and inhibits the electrochemical corrosion of Ti6Al4V, thus reducing the cavitation damage caused by the joint action of mechanical and electrochemical corrosion. However, the electrochemical corrosion of the sample was not completely inhibited after adding corrosion inhibitor.