Titanium alloy has important application value in the manufacturing of key components such as aerospace engine, but the unstable high temperature performance is the main reason that restricts its development prospect. The preparation of high temperature resistant coating on the surface of titanium alloy by laser cladding technology is an important way to give the surface special properties without changing the overall properties of titanium alloy material. At present, the high temperature resistant coatings on titanium alloys include nickel base high temperature coating, TiAl type high temperature coating and high entropy alloy coating.   

Nickel-based alloy coating has high bonding strength, good wear resistance and excellent corrosion resistance. However, due to the difference between the diffusion rate of elements in the coating and the matrix, the coating becomes unstable and the bonding strength between the coating and the matrix decreases

20201119101359429.png

TEM and EDS surface sweep of NiCrAlY/Al composite coating after corrosion for 30 h at 500 ℃

    The high temperature performance of the TiAl basic alloy is similar to that of the nickel-based superalloy with low density, which tends to replace the nickel-based alloy. Al2O3 oxide film can be generated evenly and compact on the surface of the coating. There is little difference in chemical composition between the alloy and the titanium alloy substrate, so there is basically no mutual diffusion phenomenon. However, binary gradation coating of TiAl type coating has strict requirements on the amount of Al, and its antioxidant performance will also be significantly reduced when the application temperature exceeds 850 ℃. Therefore, the addition of X elements (such as Cr, Si, Ni, etc.) in ti-al-X system coating can appropriately reduce Al content, promote the formation of uniform and dense Al2O3 oxide film, effectively prevent the diffusion of oxygen elements to the matrix, and have lower brittleness and better plasticity than binary initial TiAl coating.

20201119101434753.png

Mechanical properties of titanium alloy, TiAl type intermetallic compound and nickel base alloy    

High entropy high temperature alloy coating has many excellent properties. To adjust the content of some one or more of the following elements can be further optimized performance, which has an extremely extensive application prospect in the result. However, it is still in the laboratory research stage. The unreasonable ratio of elements, the matrix elements of the adverse effects of the cladding layer, can be a brittle and mechanical properties of high entropy alloys short of theory, the effect cannot be entered into the phase of real application.

20201119101514253.png

High temperature oxidation was tested after the FeCoCrNiAlx coating of the oxide film for its microstructure     

Using laser cladding technology to prepare high temperature anti-oxidation coating on the surface of titanium alloy is an effective way to solve the instability of high temperature performance of titanium alloy, which significantly improves the performance and service life of titanium alloy under high temperature conditions, which is of great significance for its application in aerospace and other fields. With the continuous development of science and technology, the research on it has been deepened constantly. However, due to the problems of laser technology means, coating design variables and process parameter selection, the research on it still has a long way to go. The following developments concerning the preparation of high-temperature anti-oxidation coatings by laser cladding technology are worthy of special attention:      

1) The quality of cladding layer is closely related to the technological parameters of laser cladding and the properties of cladding material. There are still many limitations and problems in the design of optimum laser cladding process parameters (such as laser power, scanning speed, etc.), which need to be constantly optimized by researchers.     

2) The cladding material system has not been completely established, which limits its development. Therefore, on the basis of satisfying the cladding layer quality, a new cladding material system should be established from the perspective of economic use. In order to further ensure the quality of cladding, in situ analysis and other techniques need to be applied in the preparation of cladding coating.     

3) A comparative analysis was made of the three most widely studied alloy coatings. The difference between the nickel base alloy coating and the matrix due to the different diffusion rates of the elements in the coating and the matrix resulted in the generation of the Kirkendall cavity. Therefore, the instability of the coating is unstable and the reduction of the bonding strength between the coating and the matrix. Although the high entropy alloy coating has great potential, it is still in the laboratory research stage. In comparison, the TiAl high temperature of super alloy coating has a better prospect in engineering application.   

4) The combination of laser cladding technology and computer numerical simulation has become an important means to optimize technological parameters and obtain high-quality cladding layer, which can reduce unnecessary waste, improve economic benefits and broaden its application range in industrial manufacturing.


The introduction on research progress of high temperature oxidation resistant coating on alloy surface

Production Technology