In the fields of energy, chemical engineering, defense, and shipping, some equipment components have long-term, full-load operation under the harsh environment of high temperature, corrosion, and mechanical wear, making these equipment components vulnerable to damage. All kinds of accidents caused by this are shocking and have seriously affected the development of social economy. How to improve the reliability and service life of these devices has become a key issue for the above industries to improve economic efficiency and enhance core competitiveness. Spraying the metal coating on the surface of the device substrate is one of the methods to solve the above problems.
Compared with stainless steel and ceramics, amorphous alloys do not have defects such as grains, grain boundaries, dislocations, and so on, and thus exhibit many excellent physicochemical properties. Among them, iron-based amorphous alloys are not only inexpensive, but also have excellent wear resistance and corrosion resistance. In recent years, the use of supersonic flame spraying technology to prepare wear-resistant anti-corrosion iron-based amorphous / nanocrystalline coating has become a research hotspot. More than 20 international scientific research institutions have developed a large number of components suitable for the preparation of iron-based amorphous alloy coatings. Among them, the neutron absorption capacity of SAM series alloy is 7 times that of stainless steel and Ni-base superalloy (C22), and it is more than 3 times that of boron steel, and its corrosion resistance is much better than that of high temperature Ni-base alloy. In addition, it also has a low coefficient of friction and thermal expansion coefficient, excellent impact toughness and wear resistance, suitable for corrosion wear protection within a wide temperature range below 650 °C. However, at present, China still lacks the thermal sprayed iron-based amorphous alloy composition with independent intellectual property rights. At the same time, the related patents applied in China are not only inferior to the SAM alloy in terms of performance, but most of the alloy compositions also fall within the scope of foreign patents.
The Amorphous Soft Magnetic Team of the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences has been working on the development and application of amorphous alloys. Recently, the research team has made progress in the design of iron-based amorphous compositions and their coating properties. By replacing the expensive rare earths, W and Mo in the SAM alloy with Ni and P, and adjusting the ratio of Cr and Mo, a series of new iron-based bulk amorphous alloys with an amorphous forming ability of more than 2 mm were obtained. High-quality spherical amorphous powders were prepared using self-constructed gas atomization equipment, and the rate of powder formation (>100 meshes) was over 80%. The study found that the alloy system can achieve excellent corrosion resistance when a small amount of Cr (8 at.%) and Mo (3.5 at.%) are added, which is not only superior to the commonly used 316L and S32750 stainless steel, but also with high Cr (15 At.%) is equivalent to Mo (14 at.%) amorphous steel (SAM1651) and the passivation film is more stable (Mater. Des., 95 (2016) 225-230). Through simple process optimization, a coating with a low oxygen content, low porosity, and high amorphous content with a thickness of 300 μm or more can be obtained. Its corrosion resistance in simulated seawater and dry friction and wear properties at room temperature are comparable to SAM-based amorphous coatings such as SAM1651 and SAM2X5, but raw material costs can be reduced by more than 50% (Surf. Eng., 2016, DOI: 10.1080/02670844.2016.1176718; Mater. Sci. Technol., 2016, DOI: 10.1080/02670836.2016.1160195). Relevant achievements have applied for 2 national invention patents.
The low cost of raw materials, excellent wear and corrosion resistance, and superior thermal stability make it attractive for applications such as hot and humid salt spray, ammonia, or various corrosive media such as acids, seawater, and sewage. In addition, the research team is currently working on the development of ultra-low magnetic and soft magnetic amorphous alloys and their coatings for use in the marine environment, and related work is well under way.
The above work was supported by the National Natural Science Foundation of China (51501210, 51571207) and Ningbo Natural Science Foundation (2015A610002).
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