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This post was last edited by B0SS on 2018-8-30 at 18:12. Plasma arc surfacing is a surfacing method that uses a plasma arc as a heat source to melt the filler metal, allowing it to bond metallurgically with the base metal. Plasma surfacing technology features energy efficiency, high performance, and stable quality, making it one of the important green manufacturing and remanufacturing technologies. With the rapid development of the domestic manufacturing industry, welding technologies, particularly plasma surfacing technology, have also seen swift progress. This article introduces the principles, applications, and future prospects of plasma surfacing technology. Keywords: plasma surfacing; technical principles; equipment and materials; processes and applications. Plasma surfacing was put into industrial use in the 1960s. It is a surfacing process that utilizes the tungsten electrode of the welding torch as the negative pole of the electric current, and the workpiece base as the positive pole; the plasma generated between them provides heat, which is then transferred to the surface of the workpiece to be welded. Welding powder is fed into this heated area, where it melts and deposits on the surface of the workpiece, thereby strengthening and hardening that surface. This surfacing technology offers advantages such as high productivity, attractive surface finish, and the ease of mechanizing and automating the surfacing process. Compared with tungsten inert gas welding, plasma surfacing features strong controllability of penetration depth, high deposition speed, and high productivity. After surfacing, the interface between the base material and the surfacing material is in a metallurgically bonded state, resulting in high bond strength, low heat input, and a low dilution rate. More importantly, due to the poor ability of the tungsten electrode to carry current, higher currents in TIG welding can cause the tungsten electrode to melt and evaporate; its particles may enter the molten pool and cause contamination. In plasma surfacing, however, the tungsten electrode needs to handle lower currents ； Compared to manual arc welding, it may be slightly inferior in terms of application flexibility and convenience, but it offers a clear advantage in production efficiency. Moreover, manual arc welding involves higher labor intensity, which can affect the welder’s health; the quality of the weld also depends heavily on the welder’s skill level and the quality of the electrodes ； Compared to submerged arc welding, it offers greater flexibility in terms of the welding position. In addition, the plasma arc itself has advantages such as concentrated heat at the arc center, stable arc, and low dilution rate. With the development of automatic control technology, CNC control is being incorporated into an increasing number of surfacing equipment, enabling precise control over key parameters such as arc voltage, current, powder feeding rate, oscillation amplitude, and oscillation frequency. Additionally, the introduction of a CNC system in surfacing systems allows for control over the movement speed of the welding gun and the movement of the workpiece. By adjusting these relevant surfacing parameters, it is possible to freely adjust the thickness, width, and hardness of the surfacing layer within certain ranges ； Compared with other surfacing techniques, less intermelting occurs between the base material and the surfacing material during plasma surfacing, resulting in minimal changes in the properties of the surfacing material ； Furthermore, the use of powder as a surfacing material increases the flexibility in alloy design, making it possible to use refractory materials for surfacing, and thus significantly enhancing the wear resistance, high-temperature resistance, and corrosion resistance of the workpiece. Therefore, plasma surfacing can be widely used in the manufacturing of new products and the remanufacturing of equipment in industries such as petroleum, chemicals, construction machinery, and mining machinery. 1. Principle of plasma surfacing technology: Plasma powder surfacing uses a plasma arc as the heat source. The high temperature generated by the plasma arc is used to rapidly heat the alloy powder and the surface of the substrate, causing them to melt, mix, diffuse, and solidify together. After the plasma beam moves away, self-cooling occurs, resulting in the formation of a high-performance alloy layer that enhances the strength and hardness of the part’s surface. Due to the high arc temperature, high heat transfer rate, good stability, and strong controllability over the depth of melting of the plasma arc, it is possible to freely adjust the thickness, width, and hardness of the surfaced layer by adjusting the relevant surfacing parameters. After plasma powder surfacing, a fused interface is formed between the base material and the surfacing material, resulting in high bond strength ； The surfacing layer has a dense structure, offering good corrosion and wear resistance ； The dilution of the base material and the surfacing material is reduced, resulting in minimal changes in the material properties ； Using powder as a surfacing material enhances the selectivity in alloy design, particularly enabling the seamless surfacing of refractory materials and improving the wear resistance, high-temperature resistance, and corrosion resistance of the workpiece. Plasma powder cladding offers high productivity, attractive surface finish, and the cladding process is easy to mechanize and automate. A plasma arc is a high-temperature, high-energy beam, with an arc temperature that can reach 30,000°C and a power density of 1.5×102 to 1.6×104 W/mm2. When plasma arcs with a high degree of compression are used for welding, cutting, and spraying, their performance can be compared to that of laser and electron beam methods ； The surfacing plasma arc with a lower degree of compression is a flexible plasma arc whose compressibility can be adjusted; it can meet the requirements for high-speed deposition in surfacing processes, fulfill the conditions for a low dilution rate, and is less prone to forming dual arcs, making it an ideal heat source for surfacing. The main form of plasma surfacing materials is powder. Since the chemical composition of the powder can be varied flexibly, the composition and properties of the plasma surfacing layer are easier to adjust compared to other surfacing methods that use wire. The most commonly used powder material in plasma surfacing is self-fluxing alloy powder. It is an alloy powder with inherent fluxing properties; no additional flux is required during welding or cladding, as the alloy itself can remove oxygen, form slag, and improve wetting. During use, two or more different types of powders (one of which can be a hard phase) can also be mechanically mixed in certain proportions to obtain surfacing alloy powders with different compositions and properties. This method is often used in experiments to rapidly create alloys with specific properties. The dilution rate of the surfacing layer is one of the most important indicators reflecting the characteristics of a surfacing method. The degree of dilution directly affects the final composition and microstructure of the surfacing layer, and ultimately determines the properties of the surface surfacing layer. Taking advantage of the good controllability of the plasma surfacing heat source, when self-fluxing alloy powders are used for surfacing, the dilution rate of the base metal in the surfaced layer can be kept within a very low range, such as 3–7%. A lower dilution rate can be achieved by using the reverse-polarity plasma surfacing method. However, an excessively low surfacing dilution rate, such as below 3%, is difficult to maintain across the entire deposition interface of conventional components, and there is a risk of incomplete fusion defects occurring. The deposition efficiency of plasma powder surfacing refers to the mass percentage of the deposited metal to the powder material used during the surfacing process; it reflects the utilization rate of the surfacing material. The degree of deposition efficiency is directly related to the production cost of plasma surfacing (especially when surfacing powder alloys with high costs). The deposition efficiency of plasma surfacing is generally around 80–95%, and under certain conditions it can exceed 95%. The deposition rate refers to the mass of weld alloy effectively deposited per unit of time; recent data show that the deposition rate in plasma powder welding can reach 12.5 kg/h or higher. (1) Building materials machinery: brick and tile factories, mixing knives, mixing baskets, counter rollers, hammer crushers, basket crushers. Cement plants, trays, tower tops, teeth, linings, jaws, rock crushers, hammers, drainage vanes, extrusion rollers, grinding rolls, excavators, shovel teeth. (2) Mining industry: coal mines, chutes, electric shovel teeth, drill bit repair. (3) Steel mill: large bell, small bell, funnel. (4) Sugar mills: Mixing and crushing for enterprises such as paper mills, construction firms, and refractory material factories. (5) Agriculture: Plowing blades, corn stalk crushing. 6. Power and cement industries: Hardfacing of turbine blades, grinding rolls, etc. 7. Petroleum and chemical industries: surfacing of drill pipes, drill bits, valves, etc. 8. Steel and coal industries: Cladding of cold (hot) rolling rolls, middle channels, wear-resistant plates, pick teeth, etc. (9) Other industries: Repair of various wear-prone parts, achieving relatively satisfactory results. Features: high hardness, high wear resistance, resistance to scouring and abrasion, etc. It has good weldability and is resistant to wear caused by rock and sand particles, extending the service life of equipment by more than 10 times.