Overview of thermal spraying technology
Development prospect of thermal spraying materials
After entering the 21st century, with the progress of science and the development of industrial production, people's demand for thermal spraying technology is expanding.This requires the thermal spraying technology to develop at a faster speed and constantly improve.However, the development of thermal spraying technology is restricted by both material and technology.In recent years, there has been a major breakthrough in thermal spraying technology, which has developed supersonic flame spraying, vacuum plasma spraying, supersonic plasma spraying, cold spraying and so on.Relatively speaking, thermal spraying materials have become the decisive factor and driving force of the development of thermal spraying technology due to their outstanding characteristics.These prominent features are mainly reflected in:
(1) a wide variety of spraying materials;
(2) the chemical composition of the spraying material can be easily adjusted;
(3) the composite of various materials can meet the requirements of many working conditions;
(4) multi-layer coating structure can have a variety of functions.
By summarizing the technical literature published in recent years and reviewing the development trend of thermal spraying materials, the following points can be roughly summarized:
1. Continuous expansion of coating function and continuous improvement of performance
With the continuous development of thermal spraying technology, more and more materials can be used in thermal spraying, so that thermal spraying coating function continues to expand, coating performance is also constantly improved.For example, TBC (thermal barrier coating) of high temperature components is one of the main application fields of thermal spraying technology.However, higher temperature and longer service life have posed challenges to thermal barrier coatings. New thermal barrier coating materials must be found or today's thermal barrier coatings must be improved. Therefore, various thermal barrier coatings have been studied.By using the high-efficiency supersonic plasma spraying technology developed successfully in recent years and adopting a new technological method to break the traditional preparation of gradient thermal barrier coating, the gradient thermal barrier coating prepared has higher thermal shock resistance performance and longer service life, showing a good research and application prospect.For another example, in the field of biomedicine, many bio-metallic and bio-activated ceramic coating materials have been applied by thermal spraying technology.Hydroxyapatite coating [HA] was originally deposited by plasma spraying to restore human function and healing.However, HA coating showed low loading capacity and crack fracture tendency.By adding Y-ZeO2 and other hard phase ceramic powders to HA, the bioceramics composite coating obtained can not only significantly improve the strength, fracture toughness and service life, but also have biocompatibility.The results show that the biocoating materials obtained by thermal spraying have great potential in the application of functional restoration, implantation and healing of human bones.
2. Composites have attracted much attention
Composite coatings not only have the properties of single structure coatings, but also can obtain coatings with special properties or multi-function.The main types of composite coatings obtained from various materials include intermetallic composite coatings, metal-based ceramic composite coatings, ceramic composite coatings, multilayer composite coatings, gradient functional composite coatings, etc.For example, Al is a coating material with good corrosion resistance, but pure aluminum has poor wear resistance. By adding hard ceramic phases AlN, Al2O3, SiC, TiC, etc. to aluminum, metal matrix composite coating can significantly improve its wear resistance.MoS2 is an excellent high temperature structural material.Its oxidation resistance, high melting point, stability in a variety of corrosion and oxidation environment, but more brittle at low temperature, in the medium temperature prone to sudden failure, so that its application is greatly limited.These shortcomings can be effectively overcome by the application of plasma spraying in the preparation of layered or gradient structure composite coatings.In short, the intermetallic composites and metal-ceramic composites, bioceramics composites and special functional composites with superior high temperature strength and oxidation resistance have become one of the important aspects in the field of thermal spraying in the future.
3. Fine grade powder has a good future
Generally, the particle size range of spraying powder is -140 mesh ~ +325 mesh, and some ceramic powder can be as fine as 5 microns or so.If the powder is too fine, it will cause burning and flying, which will increase the difficulty of powder delivery and affect the deposition efficiency.In recent years, due to the emergence of HVOF and high-energy and high-speed plasma spraying, the spraying powder is close to the fine level.The reason is that the flame flow and the particle flying speed is very high, which shortens the heating time of the particle in the flame flow, resulting in poor powder melting.However, fine powder gradation can improve the condition.At present, fine grade powder has developed rapidly and will have a better future in the future.
4. The prospect of nanomaterials is promising
In recent years, nanomaterials have become a hot topic in the field of materials science and engineering.Nanomaterials have many excellent properties compared with their corresponding micron - scale materials.With the great breakthrough in the preparation of high quality nanometer powders, the research and application of thermal spraying method to prepare nanometer grain coatings have been widely concerned.Supersonic plasma spraying is an ideal process for preparing nano-structure coatings due to its clean jet, high velocity and controllable temperature.So far, nano coatings such as al2o3-tio2, ZrO2 and 12co-wc have been prepared.The results show that the nano-coating has the characteristics of good bonding with the matrix, obvious increase of microhardness and excellent thermal stability against grain growth.However, the research of thermal spraying nanomaterials is still in the experimental stage.It is believed that the application of nanomaterials in thermal spraying technology will become a very important research direction in the future.
In short, the development of spraying materials is coordinated with the development of thermal spraying technology, with the development of thermal spraying technology and development, not only continuously meet the requirements of thermal spraying technology, but also restrict the development of thermal spraying technology.It is believed that with the application of thermal spraying technology more and more widely, the development prospect of spraying materials is very considerable.