Rapid solidification technology the first report: laser processing analysis of rapid solidification of metal materials
Rapid solidification processing technology can make microcrystalline, amorphous, quasicrystalline and other non-equilibrium new structures and other functional materials rapidly solidify. This technology can not only improve the material properties of traditional metals, but also tap the properties of existing materials and study other high-performance materials. Nowadays, the theoretical research and technology of rapidly solidified non-equilibrium materials have become one of the key research fields in materials science and condensed matter physics. The basic method to realize rapid solidification of metal materials is laser surface rapid solidification, which is also the fastest method among solidification cooling methods.
Metal materials; Rapid solidification; Laser;
Using laser to melt the surface of metal material, the surface material after rapid solidification can be obtained, and it can also have organizational characteristics. For example, dendrite and microstructure refinement, low segregation or no segregation, quasicrystal, supersaturated solid solution of solute elements, etc. And surface materials with physical, chemical or mechanical properties. In addition, in the process of laser rapid melting the surface of materials, many parts can be obtained by adding alloying elements to the molten pool. These parts are completely different in composition, microstructure and properties, and they are special surface metallurgical coating materials with fine and uniform characteristics.
Rapid solidification laser machining has the characteristics of rapidity, flexibility, easy automation and small heat affected zone, so the application foundation and research of this technology in surface modification of metal materials have developed rapidly. Moreover, laser surface alloying technology based on rapid solidification theory and laser surface engineering technology evolved from it have also become one of the new technologies of modern surface engineering. Both of these technologies can design and synthesize advanced coating materials and high-quality parts. In recent years, with the development of rapid prototyping manufacturing technology, the basic principle of processing rapidly solidified laser materials has been continuously developed, and the laser addition technology of high-performance metal parts has also developed rapidly after the combination of the two. Laser addition technology of high performance metal parts has become the key research object of laser technology, material science, material processing engineering and other disciplines. This technology is a manufacturing technology that combines material design, material synthesis and rapid prototyping of near-net-shape complex metal parts, and has the characteristics of advanced, knowledgeable and digital.
Laser cladding technology for rapid solidification of 1. titanium alloy.
Among metal materials, titanium alloy has the advantages of low density, corrosion resistance, good biocompatibility and high specific strength. And it is in great demand in aerospace, aviation, weapons, ships and other fields, so titanium alloys have been widely used. However, titanium alloy also has some disadvantages, such as low wear resistance, easy adhesion, high friction coefficient, high temperature and high speed friction, flammability and so on. But at the same time, titanium alloys are mostly used as parts of friction and wear motion pairs in these fields, and their own shortcomings can not affect the application effect. In order to improve the wear resistance, flame retardancy and friction coefficient of titanium alloy and achieve the perfect friction and wear effect of sports pair parts, advanced surface engineering technology must be adopted to change the surface defects of titanium alloy. The most economical and flexible way is to combine the base material of titanium alloy parts with solid metallurgy to form a special material with high temperature resistance, wear resistance, corrosion resistance and strong flame retardancy.
The wear resistance of titanium alloy can be greatly improved by combining laser surface alloying with laser cladding technology and surface modification layer of wear-resistant materials. In addition, the rapid solidification laser surface alloying technology is combined with laser cladding technology, and the high-temperature wear-resistant coating on the surface of titanium alloy is strengthened by refractory metal compounds to achieve the effect of rapid solidification. This method can also be applied to the development of intermetallic compound wear-resistant coating materials with high hardness and high wear resistance for titanium alloys such as TC4, BT9, TA 15. In the above coating structure, they are all intermetallic compounds, and their hardness is high, and the relationship between temperature and hardness is abnormal, and there are metal bonds and valence bonds. It is found that the friction coefficient, abrasive wear rate, sliding wear rate and fretting wear rate of these intermetallic compounds are very low at room temperature or high temperature, and their wear resistance can continue to improve, even reaching 100 ~ 700 times that of titanium alloy matrix, while their friction coefficient can be reduced by half. These studies provide a new method for the application of titanium alloy as mechanical parts of friction pairs.
Second, the rapid solidification of metal materials uses lasers to prepare new materials with special coatings.
Generally speaking, the application environment of high-temperature motion pair parts is very bad, and most of them are used in aerospace engines, oil collection equipment, power engineering and so on. Therefore, the performance of these high-temperature kinematic pair parts is extremely high, which requires not only high temperature resistance, corrosion resistance, oxidation resistance, low friction coefficient, but also strong biocompatibility. However, the new coating of this multifunctional material requires very high quality coating preparation technology. Therefore, in recent years, many researchers have combined the coating preparation technology with the rapid solidification laser cladding technology to develop powerful new coating materials, which not only greatly improved the properties of these new materials, but also further developed the solidification laser cladding coating preparation technology.
In the engine equipped with advanced technology, many high-temperature and high-speed components are needed, such as aviation devices, aerospace devices, oil collection equipment and so on. The multifunctional new coating material has the characteristics of high temperature resistance, wear resistance, oxidation resistance, low friction and friction compatibility, and is very suitable for advanced equipment such as aero-engines. In addition, a new type of laser cladding coating material with better performance, such as ultra-high carbon, can be obtained by combining the preparation technology of rapid solidification laser cladding coating with the design principle of wear-resistant materials. Its technological performance is good, its carbon content is between 9% ~ 12%, and its internal microstructure is isolated. This new material of laser cladding coating has been used as a key component of high-temperature and high-speed sliding friction pair in China's advanced aero-engines.
With the application environment of high-temperature wear-resistant sports pair parts getting worse and worse, the performance requirements are getting higher and higher. At this time, higher requirements are put forward for the chemical properties of transition metal silicide. Because refractory metal silicide can show many advantages in tribology, wear-resistant materials, surface engineering and other fields, refractory metal silicide has become another research field of new multifunctional coating materials. Through the unremitting exploration of scientific researchers, new multifunctional coating materials, such as, and, have been successfully developed. These metal silicides have excellent high-temperature wear resistance, extremely high heat resistance and corrosion resistance, low friction coefficient and friction compatibility, and they can cooperate with each other to optimize the coating laser cladding preparation technology. In the dry sliding test of normal temperature metal and high temperature metal, metal silicide coating, for example, has the characteristics of abnormal load, abnormal temperature and no friction and adhesion with metal.
Three. Liquid-solid interface structure and facet growth mechanism of metallic materials.
In the study of solidification theory, the liquid-solid interface structure, growth morphology, growth law and growth mechanism of facets have always been the key research topics. When studying the composite coating material of reinforced metal and intermetallic compound, the author studied the differences of liquid-solid interface structure, growth morphology, growth law and growth mechanism of its facets at different solidification cooling rates.
The results show that when the cooling rate is non-equilibrium solidification, the growth morphology of the facet is very graded, and when the fastest solidification condition is not reached, the liquid-solid interface structure of the facet is three-dimensional network dendrite. However, when the fastest solidification condition is reached, the faceted liquid-solid interface structure is faceted petal-shaped branched dendrite. However, no matter whether the solidification cooling rate condition is up to standard or not, even if the solidification morphology is different, the growth interface always has facet characteristics, which shows that the basic characteristics of the liquid-solid interface structure and growth mechanism of high-factor facet crystals similar to crystals will not change with the change of solidification cooling rate in a wide range.
Fourthly, rapid laser forming of high performance metal materials.
Laser rapid prototyping technology of high-performance metal materials is a new technology formed with the continuous development of material science in recent years, and it is also a kind of rapid solidification technology, which is developed by combining new material preparation technology with advanced manufacturing technology. The core of this technology is the preparation and processing technology of rapidly solidified laser materials. Using rapid prototyping manufacturing technology, parts with arbitrary shapes can be rapidly formed without using any molds and tooling. Laser rapid prototyping technology of high performance metal parts has high flexibility, adaptability and quick response, and is widely used.
Concluding remarks
With the application environment of high-temperature wear-resistant sports pair parts getting worse and worse, the performance requirements are getting higher and higher. Using laser to melt the surface of metal material, the surface material after rapid solidification can be obtained, and it can also have organizational characteristics. Rapid solidification laser machining technology is a new technology to prepare new materials by using the rapid solidification effect of metals, and it can also directly form high-performance metal materials. This technology has broad application prospects in the surface modification of many advanced aviation materials, the synthesis of new engine coating materials and the preparation of high-quality coatings.
refer to
Fan Xiong. Application analysis of laser technology in metal material processing technology [J]. Enterprise technology development, 20 13, 15: 23-24.
[2] Tian Yanlong. Application analysis of laser technology in metal material processing technology [J]. Scientific and technological innovation and application, 20 13, (10).
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