Wear-resistant Surface Modification and Coating Technology of Titanium

Thermal Spray

Ion Implantation

Ion implantation technology began in the 1960s. This technology rapidly injects high-energy charged ions into the near surface of the metal under vacuum and low temperature, causing a series of complex reactions between the ions and the matrix to form a new surface-modified alloy layer. The newly formed alloy layer has a strong bonding force with the substrate, and the wear resistance is improved significantly. The outstanding advantage of the process is that it can maintain the performance of the metal matrix itself, does not change the macroscopic size of the material. It is environmentally friendly and pollution-free, and can greatly improve the corrosion resistance and oxidation resistance of the surface of the material. The ion source can be a non-metal ion such as B, C, N, etc., or a metal ion such as Zr, Mo, Re. In the case of non-metal ion implantation, when B, C, O, etc. are implanted into the surface of the titanium alloy, corresponding hard compounds (TiB, TiC, TiO) are formed, so that the surface hardness and wear resistance of the material are improved. Scientists injected N3- into the surface of Ti6Al4V substrate to improve the mechanical properties of the material. The TiN film formed significantly improved the microhardness of the titanium alloy surface, and the average hardness increased by about 25%, and the wear resistance was 2.5 times that of the titanium alloy matrix.

Ion Implantation

Electroless Plating

Electroless plating is also called autocatalytic plating. It is a surface plating technique using the autocatalytic action of metal and reducing the free metal ions to metal by means of a reducing agent in the plating solution without uniform current to deposit a film on the surface of the part to be plated. At present, in terms of wear modification of titanium alloys, electroless plating has been gradually developed from the initial single electroless Ni plating to various metal and alloy and composite electroless plating surface treatment processes, such as electroless plating of Cu, Ag, Au and Sn. The composite electroless plating is based on the original plating solution to add solid hard particles such as Al2O3, Cr2O3, SiC, etc., so that it can co-deposit with the metal under external force, thereby obtaining better mechanical properties than the coating without particles.

Scientists have tried to make Ni-P-polytetrafluoroethylene (PTFE) composite coating on the surface of titanium alloy by electroless plating technology, and studied the influence of plating solution concentration, temperature and surfactant concentration on the formation of coating, and also explored Friction and wear characteristics of the sample. The results show that the co-deposition of Ni-P and PTFE can significantly reduce the friction coefficient of the coating, reduce the wear and improve the lubrication performance.

Compared with electroplating, the electroless plating layer has the advantages of uniform density, no need for external current supply, simple operation process, deposition of plating on non-conductors such as plastics, and the like, and the electroless plating has low pollution and low cost. At present, electroless plating can be widely used in aerospace, automotive, machinery, chemical and other fields because it can prepare a film layer with good corrosion resistance and wear resistance.

Laser Cladding

Laser cladding technology is a surface modification technology that combines laser technology with metal heat treatment technology. This technique forms a good metallurgical bonding layer on the base metal by spraying or bonding the powder material on the surface of the substrate in advance, or by feeding the powder synchronously with the laser beam, and then irradiating the surface of the material with a high energy density laser beam. Due to the small amount of melting of the substrate during laser cladding, there is substantially no effect on the performance of the substrate. At present, there are not many cladding materials that have been used to improve the wear resistance of titanium alloys. Commonly used are hard ceramics (SiC, TiC, Al2O3, TiN and TiB2, etc.), nickel-based self-fluxing alloys and ceramics/alloys. Among them, the single hard ceramic laser cladding layer has high brittleness and does not match the thermal expansion coefficient of the titanium alloy, resulting in high residual stress, which may cause cracks or even fall off of the cladding layer. Therefore, ceramics/alloys are commonly used to improve the wear resistance of titanium alloys, in which the alloys are mostly self-melting NiCrBSi alloys.

Laser cladding

The researchers laser-clad different amounts of SiC on the surface of TC4 titanium alloy. During the whole process, SiC reacted with the matrix to form Si5Si3 and TiC. The formation of the reactant significantly improved the hardness and wear resistance of the matrix titanium alloy. The experimental results show that the hardness of the coating after laser cladding SiC of titanium alloy reaches 1200 HV, which is more than three times the hardness of the substrate, and the wear resistance of the coating is also increased by 18.4~57.4 times; and with the increase of SiC addition content (low At 20% (mass fraction), the hardness of the coating is gradually increased to 1300~1600 HV, and the wear resistance is further improved.

Thermal Spray

Thermal spraying uses a certain heat source to heat the spray material. After the material to be sprayed is in a flowable state, it is accelerated by the flame flow, and then sprayed onto the surface of the pretreated substrate to deposit a processing method with a specific functional coating. The commonly used spray materials for titanium alloy wear-resistant modification are generally non-metallic materials such as nickel-coated graphite, elemental metal materials such as Al, Ni, and alloy materials such as TiN, NiCrAl, and MCrAlY. After the thermal spraying treatment, the interface between the coating and the substrate is straight and the bonding is good, and in the subsequent high-temperature oxidation process, the spraying material and the substrate mutually diffuse to form a metallurgically bonded diffusion layer, so that the wear resistance is greatly improved. Scientists introduced that a thermal sprayed aluminum coating on the surface of a titanium alloy can deposit a protective layer on the surface of the substrate, but the protective layer is hard and brittle at low temperatures, and is prone to flaking due to mismatch in thermal expansion coefficient.

Thermal Spray

Physical Vapor Deposition

Physical vapor deposition technology is a technique in which a material source (solid or liquid) surface is vaporized into a gaseous atom, a molecule or a part of ionized into an ion under vacuum and transported to a surface of a substrate to form a solid phase film. Physical vapor deposition techniques mainly include evaporation, sputtering, and ion plating, and can be used to prepare metal films as well as compound films. Related: Aluminum Titanium Sputtering Target

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