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Surface treatment of titanium alloys

Any material has its advantages and disadvantages, in order to further improve corrosion resistance and wear resistance of titanium alloy, the micro wear resistance, high temperature oxidation resistance and other purposes, the titanium alloy surface treatment is an effective way of further expanding the scope of the titanium alloy used, you can say that the current in metal surface treatment methods for almost all applications to the surface treatment of titanium alloy, including metal plating, electroless plating, thermal diffusion, anodic oxidation, thermal spraying, low pressure ion technology, electron and laser surface alloying, unbalanced magnetron sputtering deposition, ion nitriding, PVD legal membranes, ion plating, nano technology and so on.In general, the formation of TiO, TiN, TiC coating and TiAlN multilayer nanofilms on the surface of titanium alloy is still the focus.

Electroplating: nickel plating, hard chromium plating, silver plating on the surface of titanium alloy.The purpose of silver plating is to improve the conductivity and brazing of titanium alloys.Titanium alloy matrix has a layer of dense oxide film, electroplating is not easy, so the surface of titanium alloy must be pretreated before electroplating.

Ac microarc oxidation (MAO) is a new technique for growing oxide ceramic films on metal surfaces.It developed from anodic oxidation, but it applied a high voltage of several hundred volts, breaking the voltage limit of anodic oxidation.This technology directly transforms the matrix metal into oxide ceramics through instantaneous high temperature and high pressure sintering in the micro-arc discharge area, and obtains a thicker oxide film.The micro-arc oxidation film on the surface of titanium alloy was obtained with high hardness and good bonding with the metal matrix.The properties of the surface of titanium alloy such as wear resistance, corrosion resistance, heat shock resistance and insulation have been improved.

Surface oxidation treatment: general titanium and titanium alloy than commonly used biological alloy CoCr alloy and 316L stainless steel wear resistance are poor, and the wear powder produced in the biological body may have adverse effects.Therefore, some newly developed biological titanium alloys in vivo before use in the biological body often need to take appropriate surface treatment to improve its wear resistance.To this end, a newly developed biological titanium alloy Ti29Nb13Ta46Zr(TNTZ alloy for short) was studied by fengqiao university of technology and datong special steel company in Japan.

Ion implantation: ion implantation and other surface treatment techniques

Compared with physical or chemical vapor deposition, the main advantages are:

  1. (1) film and matrix combination, resistance to mechanical, chemical action without peeling ability;

  2. (2) the injection process does not require the increase of the substrate temperature, so as to maintain the workpiece geometric precision;

  3. (3) good repeatability and so on.Many researchers have reported that nitrogen ion implantation can improve the surface composition, microstructure, hardness and tribological properties of Ti6Al4V alloy.

TiC is also a superhard phase, so the surface of titanium alloy can also be strengthened by ion implantation of carbon.However, since plasma-based ion implantation is not a continuous process, sputtering and injection occur when every negative impulse potential is applied, as the impulse potential drops from zero to a valley value and then rises back to zero.If the plasma contains metal or carbon ions, when the impulse potential is zero, a single carbon deposition layer will be formed on the surface under certain conditions. Under a certain impulse voltage (10~30kV), the structure of this single carbon layer is diamond-like carbon (DLC).Thus, the surface modification layer with lower friction coefficient and better wear resistance can be obtained.The single carbon layer on the surface was confirmed as DLC film by experiments.After such treatment, the surface hardness of titanium alloy increased by 4 times, in the same material constituted friction pair, dry friction conditions, friction coefficient from 0·4 down to 0·1, wear resistance than no ion implantation increased by more than 30 times.

Ion beam enhanced deposition (IBED): CrC hard film was prepared by ion beam enhanced deposition (IBED) method, which can be used for fretting wear protection of titanium alloys.The results showed that CrC showed the best fretting fatigue characteristics.The CrC film coated after shot peening showed the highest fretting wear resistance.

Coating technology: coating technology is an effective method to improve the oxidation resistance of titanium alloys.A us company has developed a new method to improve the oxidation resistance of titanium alloys by coating them with a uniform copper alloy.The copper alloy used in the coating can be selected from one of the following three components :1· copper +7% aluminum;2· copper +4·5% aluminum;3· copper +5·5% aluminum +3% silicon.The coating is applied at a substrate temperature below 619℃.

Laser quenching: the fretting wear of titanium alloy TC11 is reported to increase with the increase of normal load and fretting amplitude.After laser quenching, the anti-fretting wear ability of titanium alloy TC11 was improved, the increase range and the fretting range were improved, and the improvement of anti-fretting wear ability was the result of the microstructure refinement and hardness enhancement caused by laser quenching.

Titanium alloy laser cladding: aviation engine nickel-based alloy friction pair of fretting wear is a big problem in aircraft engine use, using laser cladding technology can obtain excellent coating, for gas turbine engine components repair opened a new way of cladding alloy powder is CoCrW and mechanical mixture of WC, improves the high temperature wear resistance and corrosion resistance, the technology is characterized by short preparation time, stable quality, and eliminate the effects due to thermal possible crack problems.

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 with a hardness of 600~800HV.The increase of surface hardness is beneficial to improve the wear resistance of TC11 titanium alloy.

Plasma nitriding and shot peening treatment: use dc pulse plasma power supply system on Ti6Al4V titanium alloy surface nitriding treatment, the shot peening deformation strengthening (SP) to the post-processing of nitriding layer, in the surface of titanium alloy by TiN, Ti2N, Ti2A1N phase composition of the nitriding layer, the modified layer can significantly improve normal titanium alloy wear and fretting wear resistance (FW), but reduces the FF strength of base material.The friction reduction and wear resistance of nitriding layer and the surface residual compressive stress introduced by SP work together to make the FF resistance of titanium alloy exceed that of SP alone.It is very important to improve the FF and FW properties of titanium alloys by increasing the toughness of nitriding layer.

DLC film: composite carbon film has unique physical, mechanical and chemical properties, it has been as a number of research objects.Diamond-like films were prepared by rf plasma-enhanced chemical vapor deposition (CVD), the main purpose of which was to improve the surface hardness and friction resistance of titanium alloys.The results show that when the content of titanium in the membrane exceeds 9%, the hardness of the membrane will decrease, and the strength of the membrane base bonding force is also limited.

Liquid phase deposition: liquid phase deposition of bioceramic coating on the surface of TC4.In recent years, exploratory studies on the preparation of bioceramic coatings on titanium alloy substrates by chemical treatment have been reported.Such as high concentration of NaOH or H2O2 treatment process, the proposed two-step alkali treatment process, and the introduction of preparation such as vinyl triethoxysilane and sodium polyacrylate to obtain the bioceramic coating.After simple acid and base pretreatment, TC4 alloy was immersed in a humoral-like fast calcification solution (FCS) to obtain a gradient-bonded bioactive titania-based HA bioceramic coating composite.The study of this method is of great theoretical significance and potential economic value for the direct use of titanium alloys as hard tissue implant materials.


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