Preparation of the hottest sprayed amorphous alloy

Preparation of thermal sprayed amorphous alloy coating

thermal spraying technology is a very important technology in the field of surface engineering. Its development trend is: equipment (spraying gun) is developing towards high energy, high enthalpy and high speed; In terms of materials, it is developing towards serialization, standardization and commercialization to ensure the needs of multi-functional and high-quality coatings; The process is developing towards mechanization and automation, such as juice calculation and hunger control, manipulator operation, etc With the research and development of amorphous materials and the continuous emergence of various new and high-quality thermal spraying technologies (such as high-speed flame spraying HVOF, high-speed arc spraying HVAS and supersonic ion spraying SPS, which have won time for enterprises), thermal spraying of non structural coatings is becoming an important development direction of thermal spraying technology

compared with traditional coatings, amorphous structure coatings will significantly improve in strength, toughness, corrosion resistance, wear resistance, thermal barrier and thermal fatigue resistance, and some coatings have the above-mentioned properties at the same time. The basic problems of non-metallic coating research in thermal spraying technology include the interface between amorphous coating and substrate; Physical, metallurgical and chemical processes of non-ferrous powder materials in the dynamic preparation of thermal sprayed coatings; Synergistic effect between non-metallic powder materials and other materials in thermal sprayed coatings

I. performance characteristics of amorphous alloys

1. Mechanical properties of amorphous alloys

(1) the strength of common structural materials with high tensile strength, such as magnesium alloy, duralumin, titanium alloy, stainless steel, super strong steel, is significantly different from that of new non-ferrous materials. For example, the strength of Al based and Mg based amorphous alloys with light specific gravity is 2-3 times that of the corresponding crystalline materials. The strength of Mg alloy with low strength can reach more than 1000MPa after obtaining amorphous structure. The maximum strength of Al based amorphous alloy can reach 1200Mpa. If the structure with nano-sized FCC Al particles dispersed on the amorphous matrix can be obtained, the strength can reach about 1550mpa. This high strength Al based alloy makes it possible to obtain new advanced materials with high specific strength

(2) the hardness of high hardness amorphous alloys is significantly higher than that of corresponding crystalline materials, for example, the Vickers hardness of fe-b-based amorphous alloys reaches more than 1200. The relationship between the hardness and strength of amorphous alloys and Young's modulus is basically the same, so amorphous alloys truly reflect the hard and strong properties of materials

(3) low modulus amorphous alloys have lower Young's modulus and better elasticity than the corresponding crystalline metals. At the same time, amorphous alloy fittings have higher elastic elongation and higher elastic energy. In addition, amorphous also has excellent mechanical properties such as high bending strength and fracture toughness

2. Other properties of amorphous alloys

amorphous alloys have long-range disordered structures, but compared with the disorder of liquids, they also have some short-range ordered short-range ordered domains. Unlike ordinary polycrystalline materials, non-metallic alloys have a wide supercooled liquid region before crystallization Δ Tx。 The supercooled liquid phase region is unique to the alloy with the ability to form bulk amorphous. As long as the amorphous forming ability of the alloy is strong, whether it is bulk or low dimensional amorphous ribbon, powder, wire, etc., it will have this region. In the supercooled liquid phase region, before the amorphous alloy is crystallized by heating, it can maintain the "frozen" liquid structure within a certain temperature range, showing properties very similar to oxide glass with a certain viscosity, and Newtonian flow can occur, that is, the strain rate sensitivity index m=1（ σ= K ×ε m)。 Therefore, amorphous alloys are sometimes called metallic glasses, which not only have the characteristics of metals, but also show the performance characteristics of some oxide glasses. The viscous flow of the crystalline alloy in the supercooling temperature range of the oil suction filter and filter element that are changed irregularly makes the alloy have superplastic forming ability

compared with the Superplasticity of ordinary polycrystalline materials, the Superplasticity of amorphous alloys has the following advantages: paper mills have only one card to play because of the shortage of raw materials:

(1) the deformation temperature is low, and the superplastic deformation of amorphous alloys occurs in the supercooling temperature zone, generally below 0.6T

(2) with a high strain rate e, amorphous alloys have a wide Newtonian flow range, so higher strain rates can be obtained

(3) the external force required for deformation is small, and the amorphous is in a viscous flow state when plastic deformation occurs, so the deformation force required is small

(4) there is no cavity in the deformation process. When superplastic deformation occurs in ordinary polycrystalline materials, the grain will slip, rotate, and even move perpendicular to the free surface. Therefore, the generation of cavity is inevitable and is a serious defect, which can be fundamentally eliminated by the Newtonian flow state of non-metallic materials

(5) uniform deformation occurs in both micro and macro

(6) the original properties will remain after deformation. As long as the deformation process is controlled in the supercooling temperature range where Newtonian flow occurs, the alloy will remain amorphous after cooling, and the properties will not change

(7) deformation with extremely complex shape can be carried out. Superplastic deformation of crystalline materials can only be carried out for workpiece with relatively simple shape, while the forming of amorphous alloy is not limited. For structural parts with complex shape, its forming ability will be more prominent

there is no grain boundary, precipitate phase boundary, dislocation and other parts that are easy to cause local corrosion in the non-metallic alloy, and there is no component segregation that is easy to occur in the metallic alloy. Therefore, the amorphous alloy is more uniform in structure and composition than the crystalline alloy, so it has higher corrosion resistance, and its corrosion resistance is 100 times that of the crystalline stainless steel. At the same time, amorphous alloys usually do not have the pinning effect of obstacles such as precipitate particles on the domain walls, so they have excellent soft magnetic properties

3. explosive spraying amorphous alloy coating

h.w.jin et al. Studied the microstructure and wear resistance of explosive spraying Fe-Cr-B alloy coating. The results show that the coating has good anti-wear and anti-corrosion properties. During the sliding wear process, the coating dynamically produces an amorphous surface facial mask, which significantly improves the wear resistance of the coating and significantly reduces the friction coefficient

4. Arc sprayed amorphous alloy coating

the design idea of preparing amorphous alloy coating by arc spraying is: take the selected amorphous alloy powder as the core and the metal as the outer skin to prepare powder core wire for arc spraying, and then obtain the amorphous alloy arc spraying layer. A. I.brisova et al. Successfully prepared fe-b-re amorphous coating by adding rare earth elements into Fe-B by arc spraying process. Guojinhua of Northeastern University in China has prepared two kinds of Fe based amorphous coatings by arc spraying, and the microhardness of the coatings is more than 1000. Beijing University of technology has been committed to the research of thermal spraying materials since the 1980s. The arc sprayed amorphous alloy coating has high hardness (>1000hv), high bonding strength (>55mpa) and good wear resistance. In the wet rubber wheel friction and abrasive test, its relative wear resistance is more than 7 times that of the commercial 3Crl3 coating. In the circulating fluidized bed boiler pipeline heating surface wear-resistant protection, all kinds of induced draft fan and powder exhauster impeller, steel plant converter smoke hood and flue and other high wear-resistant and corrosion-resistant protection have achieved good results. At the same time, it is also the first research institute to apply for the patent of wire for arc spraying amorphous coating (two invention patents have been patented, namely, the preparation of powder core wire for amorphous coating containing CRB by arc spraying (Patent No.: zl.9) and the preparation of powder core wire for amorphous coating containing NIB by arc spraying (Patent No.: zl200 (order.3))

III. problems and development prospects of thermal spraying amorphous alloy coating

due to the short time of research and development, the coating can not meet the design requirements. The amorphous content in the coating is difficult to reach 100%. The prepared coating has poor density, and the coating performance is far from that of bulk amorphous alloy. In this sense, the coating performance has not yet developed, and there is still a lot of room

at present, the domestic research level in this field is still far behind that of developed countries such as the United States. The domestic research on thermal sprayed amorphous alloy materials is still in the stage of experimental research. From the existing research results, the amorphous alloy coating prepared by thermal spraying technology has excellent corrosion resistance and wear resistance, and has a good application prospect. At present, China has also strengthened the research of amorphous nanocrystalline structure coating. It is believed that the thermal spraying amorphous alloy coating technology will play an important role in China's economic construction in the near future. (end)