What are the surface treatment methods for titanium alloys?
titanium alloy are broadly utilized in aviation, chemical industry and biomedical fields. Nonetheless, their low hardness and unfortunate enemy of wear and contact diminishing properties limit their applications. the utilization of surface adjustment innovation to work on a superficial level properties of titanium alloy has drawn in much consideration. Chemical treatment or chemical oxidation is usually the most common method for increasing the bonding force between the substrate and the coating layer and the surface's resistance to corrosion. Notwithstanding, However, the oxide film obtained by chemical oxidation is thin and has poor corrosion resistance and durability. Chemical plating and electroplating on titanium are difficult because of the oxide film on its surface. In contrast, micro-arc oxidation treatment is generally regarded as the most promising titanium alloy surface treatment method at the moment.
Generally, titanium and titanium alloys have poorer wear resistance than the commonly used biological alloys CoCr alloy and 316L stainless steel, and the wear powder produced may have adverse effects in the biological body. Therefore, some newly developed titanium alloys for biological use often require appropriate surface treatment to improve their wear resistance before being used in vivo. In order to further improve the corrosion resistance, wear resistance, fretting resistance, high temperature oxidation resistance, etc. of titanium alloys, surface treatment of titanium alloys is an effective way to further expand the scope of use of titanium alloys. It can be said that the current use of metals Almost all of the surface treatment methods have been applied to the surface treatment of titanium alloys, including metal plating, chemical plating, thermal diffusion, anodizing, thermal spraying, low-pressure ion technology, electronic and laser surface alloying, and non-equilibrium magnetron sputtering coating. , ion nitriding, PVD film production, ion plating, nanotechnology, etc. It seems that the formation of TiO, TiN, and TiC infiltration coatings on the surface of titanium alloys and the surface oxidation treatment of TiAlN multilayer nanofilms to improve their surface wear resistance are still the focus of research.
Liquid deposition: Liquid deposition bioceramic coating on TC4 surface. In recent years, exploratory research on preparing bioceramic coatings on the surface of titanium alloy matrix implants through chemical treatment has been publicly reported. For example, the two-step alkali treatment process proposed by using high-concentration NaOH or H2O2 treatment process, and some people have introduced modulators such as vinyl triethoxysilane and sodium polyacrylate to obtain bioceramic coatings. After simple acid-base pretreatment, TC4 titanium alloy is immersed and deposited in a rapid calcification solution (FCS) that simulates body fluid, in order to obtain gradient-bound titanium-based HA bioceramic coating composites with good biological activity. The study of this method has very important theoretical significance and potential economic value for the direct application of titanium alloys as hard tissue implant materials.
Surface oxidation treatment: Compared with other surface treatment technologies, ion implantation shows many advantages. Compared with physical or chemical vapor deposition, the main advantages are: ① The film is well combined with the substrate, and has strong resistance to mechanical and chemical effects without peeling off; ② Implantation The process does not require an increase in substrate temperature, thereby maintaining the geometric accuracy of the workpiece; ③ The process has good repeatability, etc. Many researchers have reported that nitrogen ion implantation has a good effect on improving the surface composition, microstructure, hardness and tribological properties of Ti6Al4V titanium alloy. TiC is also a superhard phase, so ion implantation of carbon into titanium alloys can also strengthen the surface of titanium alloys. However, since plasma-based ion implantation is not a continuous process, when each negative pulse potential is applied, as the pulse potential drops from zero to the valley value, and then rises back to zero, two processes, sputtering and implantation, occur. If the plasma contains metal or carbon ions, when the pulse potential is zero, a single carbon deposition layer will be formed on the surface under certain conditions. Under a certain pulse voltage (10~30kV), the structure of this single carbon layer will is diamond-like carbon (DLC). As a result, a surface modification layer with lower friction coefficient and better wear resistance than the nitrogen-injected layer can be obtained. The single carbon layer on the surface was experimentally determined to be a DLC film. The surface hardness of the titanium alloy treated in this way is increased by 4 times. When the same material forms a friction pair, under dry friction conditions, the friction coefficient drops from 0·4 to 0·1, and the wear resistance is more than 30 times higher than that without ion implantation. .
Ion beam enhanced deposition (IBED): A CrC hard film was prepared using the ion beam enhanced deposition (IBED) method, which can be used for fretting wear protection of titanium alloys. Research shows that CrC shows the best fretting fatigue characteristics; and the CrC film coated after shot peening shows the highest fretting wear resistance. Ion bombardment: After surface treatment of TC11 titanium alloy by nitrogen ion bombardment, a modified layer composed of TiN and Ti2N can be obtained on the surface, with a hardness of 600~800HV; the increase in surface hardness is conducive to improving the wear resistance of TC11 titanium alloy. Plasma nitriding and shot peening: DC pulse plasma power supply device is used to nitriding the surface of Ti6Al4V titanium alloy, and shot peening deformation strengthening (SP) is used to post-process the nitriding layer. TiN, Ti2N, and Ti2A1N are obtained on the surface of the titanium alloy. A nitrided layer composed of equal phases, this modified layer can significantly improve the conventional wear and fretting wear (FW) resistance of titanium alloys, but reduces the FF resistance of the base material. The friction-reducing and anti-wear properties of the nitrided layer work synergistically with the surface residual compressive stress introduced by SP, making the titanium alloy FF resistance exceed that of SP alone. Improving the toughness of the nitrided layer is very important for improving the FF and FW properties
of titanium alloys. DLC membrane: Composite carbon membrane has unique physical, mechanical and chemical properties, and it has been used as the object of numerous studies. The main purpose of using radio frequency plasma enhanced chemical vapor deposition method to prepare diamond-like carbon films is to improve the surface hardness and friction resistance of titanium alloys. The test results show that if the titanium content in the film exceeds 9%, the hardness of the film will decrease, and the bonding strength of the film base is also limited.
AC micro-arc oxidation: Micro-arc oxidation (MAO) is a new technology for growing oxide ceramic films on metal surfaces. It developed from anodizing, but it applied a high voltage of several hundred volts, breaking through the voltage limitations of anodizing. This technology directly turns the base metal into oxide ceramics through instantaneous high-temperature and high-pressure sintering in the micro-arc discharge zone, and obtains a thicker oxide film. For the micro-arc oxidation film on the surface of titanium alloy, the hardness of the film obtained is high and it is well combined with the metal matrix. It improves the wear resistance, corrosion resistance, thermal shock resistance and insulation properties of the titanium alloy surface, and has application prospects in many fields.
