Surface treatment of titanium alloy

Any material has its advantages and disadvantages. In order to further improve the corrosion resistance, wear resistance, fretting wear resistance and high temperature oxidation resistance of titanium alloy, surface treatment of titanium alloy is an effective way to further expand the application range of titanium alloy. It can be said that almost all the surface treatment methods of metal are applied to the surface treatment of titanium alloy, It includes metal plating, electroless plating, thermal diffusion, anodizing, thermal spraying, low-pressure ion process, surface alloying of electron and laser, unbalanced magnetron sputtering coating, ion nitriding, PVD coating, ion plating, nanotechnology and so on. In general, the formation of TiO, tin, TiC coating and TiAlN multilayer nano film on the surface of titanium alloy is still the focus.

Electroplating: nickel plating, hard chromium plating and silver plating on the surface of titanium alloy. The purpose of silver plating is to improve the conductivity and solderability of titanium alloy. There is a dense oxide film on the titanium alloy substrate, which is difficult to be electroplated. Therefore, the surface of titanium alloy must be pretreated before electroplating.

AC micro arc oxidation: micro arc oxidation (MAO) is a new technology for growing oxide ceramic films on metal surfaces. It developed from anodic oxidation, but it applied a high voltage of several hundred volts, breaking through the limitation of anodic oxidation on voltage. In this technology, the base metal is directly transformed into oxide ceramics by the instantaneous high temperature and high pressure sintering in the micro arc discharge zone, and the thick oxide film is obtained. The micro arc oxidation film on the surface of titanium alloy has high hardness and good bonding with metal matrix. It can improve the wear resistance, corrosion resistance, heat shock resistance and insulation properties of titanium alloy surface, and has application prospects in many fields

Surface oxidation treatment: the wear resistance of general titanium and titanium alloy is worse than that of CoCr alloy and 316L stainless steel, and the wear powder produced may have adverse effects in organism. Therefore, some newly developed titanium alloys for biological use should be treated properly before they are used in vivo to improve their wear resistance. Therefore, a newly developed β – type titanium alloy ti29nb13ta46zr (TNTZ alloy for short) was developed by Toyohashi University of technology and science and Datong special steel company. The surface oxidation treatment was adopted to improve the surface wear resistance.

Ion implantation: compared with other surface treatment technologies, ion implantation shows many advantages. Compared with physical or chemical vapor deposition, the main advantages are as follows:

• ① The film is well bonded with the substrate, and has strong resistance to mechanical and chemical action;
• ② It is not necessary to increase the substrate temperature during the injection process, so that the geometric accuracy of the workpiece can be maintained;
• ③ The process has good repeatability. Many researchers have reported that nitrogen ion implantation can improve the surface composition, microstructure, hardness and Tribological Properties of Ti6Al4V alloy.

Therefore, the surface of titanium alloy can also be strengthened by ion implantation of carbon. However, due to the fact that plasma based ion implantation is not a continuous process, when each negative pulse potential is applied, as the pulse potential decreases from below zero to the valley value, and then rises to zero, there are two processes of sputtering and implantation. If the plasma contains metal or carbon ions, a single carbon deposition layer will be formed on the surface under certain conditions when the pulse potential is zero. Under a certain pulse voltage (10 ~ 30 kV), the structure of the single carbon layer is diamond-like carbon (DLC). Thus, the surface modified layer with lower friction coefficient and better wear resistance can be obtained. A single carbon layer on the surface was determined to be DLC film by experiments. The results show that the surface hardness of the titanium alloy treated in this way is increased by 4 times, and the friction coefficient decreases from 0.4 to 0.1 under dry friction condition, and the wear resistance of titanium alloy is increased by more than 30 times than that without ion implantation.
Ion beam enhanced deposition (IBED): CRC hard films were prepared by ion beam enhanced deposition (IBED), which can be used for fretting wear protection of titanium alloys. The results show that the CRC shows the best fretting fatigue property, while the CRC film coated after shot peening shows the highest fretting wear resistance.

Coating technology: coating technology is an effective method to improve the oxidation resistance of titanium alloy. An American company has developed a new method to improve the oxidation resistance of titanium alloy by adding a uniform copper alloy coating on the titanium alloy substrate. The copper alloy used in the coating can be selected from the following three components:

• 1. Copper + 7% aluminum;
• 2. Copper + 4.5% aluminum;
• 3. Copper + 5.5% aluminum + 3% silicon. The coating was applied when the substrate temperature was lower than 619 ℃.

Laser quenching: it is reported that the fretting wear of TC11 titanium alloy increases with the increase of normal load and Fretting Amplitude. After laser quenching, the fretting wear resistance of titanium alloy TC11 has been improved. The improvement of fretting wear resistance is the result of microstructure refinement and hardness improvement.
Laser cladding: the contact wear of titanium alloy and nickel base alloy friction pair of aeroengine is a big problem in the use of aeroengine. The excellent coating can be obtained by laser cladding technology, which creates a new way for the repair of gas turbine engine parts. The cladding alloy powder is the mechanical mixture of CoCrW and WC, which improves the high temperature wear resistance and corrosion resistance, The technical features are short preparation time, stable quality and elimination of cracks due to thermal effect.
Ion bombardment: after the surface treatment of TC11 Titanium Alloy by nitrogen ion bombardment, the modified layer composed of tin and Ti2N can be obtained, and the hardness is 600 ~ 800hv; the improvement of surface hardness is conducive to improving the wear resistance of TC11 titanium alloy.
Plasma nitriding and shot peening: the surface of Ti6Al4V titanium alloy was nitrided by DC pulse plasma power supply, and the nitriding layer was treated by shot peening deformation strengthening (SP). The nitriding layer composed of tin, Ti2N, ti2a1n and other phases was obtained on the surface of titanium alloy. The modified layer can significantly improve the resistance of conventional wear and fretting wear (FW), but reduce the FF resistance of the substrate. The friction reducing and antiwear properties of nitriding layer and the surface residual compressive stress introduced by SP synergistically make the FF resistance of titanium alloy exceed that of SP alone. Increasing the toughness of nitriding layer is very important to improve the properties of FF and FW of titanium alloy.
DLC film: composite carbon film has unique physical, mechanical and chemical properties, it has been used as a number of research objects. The main purpose of diamond-like carbon (DLC) films prepared by RF plasma enhanced chemical vapor deposition is to improve the surface hardness and friction resistance of titanium alloys. The results show that if the content of titanium in the film is more than 9%, the hardness of the film will decrease, and the adhesion strength of the film to substrate is also limited.
Liquid deposition: bioceramic coating was deposited on TC4 surface. In recent years, the exploratory research on Preparation of bioceramic coating on titanium alloy implant surface by chemical treatment has been reported publicly. For example, high concentration NaOH or H2O2 treatment process, the two-step alkali treatment process proposed, and some modulators such as vinyl triethoxysilane and sodium polyacrylate were introduced to obtain bioceramic coating. TC4 alloy was pretreated by acid and alkali, and then immersed in a kind of fast calcification solution (FCS) simulating body fluid to obtain titanium matrix ha bioceramic coating composite with good bioactivity by gradient bonding. The research of this method has very important theoretical significance and potential economic value for titanium alloy as hard tissue implant material.

Source: China Titanium Flanges Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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