A review of the research and application of copper-nickel alloys, including research on the classification, properties and applications, and performance requirements of copper-nickel alloys
Abstract: The rapid development of the marine industry has placed increasing demands on marine engineering application materials, including white copper, which is widely used in ships, some power plants, and seawater desalination. Because it is subject to long-term seawater erosion and corrosion, if the corrosion resistance does not meet the usage requirements, corrosion failure will occur, resulting in huge losses. Therefore, white copper has attracted increasing attention due to its good seawater corrosion resistance (especially good erosion corrosion performance) and corrosion fatigue resistance, excellent cold and hot processing performance, and high tensile strength, yield strength and other properties.
Keywords: white copper; composition; corrosion resistance; application
CTL classification number: TG146.15 Document code: A
With the development of the marine industry, the material selection of seawater cooling systems has evolved from the early TUP copper, aluminum brass, and stainless steel to the current copper-nickel alloy with better resistance to seawater corrosion. White copper uses nickel as the main element and contains a small amount of Fe, Mn and other elements to form a continuous α-single-phase solid solution, giving it good ductility, impact resistance and thermal stability. At the same time, the infinite solid solution of copper and nickel prevents phase transformation during later hot and cold processing, so it has little impact on the mechanical properties and corrosion resistance of the alloy. This article introduces different white copper alloys and their applications, and summarizes the research progress of copper-nickel alloys. Figure 1 shows the offshore platform system, and Figure 2 shows the material performance requirements.
1. Classification of copper-nickel alloys
Table 1 shows the grade and elemental composition of cupronickel alloy. Cupronickel can be divided into manganese cupronickel, iron cupronickel, ordinary cupronickel, aluminum cupronickel and zinc cupronickel. Due to the different content of Ni element, its properties are different, and the application occasions are also different. different. Because of its irreplaceable corrosion resistance and many properties superior to traditional alloys, it has great application potential.
2. Properties and applications of copper-nickel alloys
Ordinary white copper is generally a structural copper-nickel alloy. In addition to its high corrosion resistance, it also has good comprehensive mechanical properties at high and low temperatures, that is, good plasticity and toughness. It is generally used as rods or strips. At the same time, adding some trace alloy elements such as Fe, Mn, Zn and Al on the basis of ordinary white copper can achieve special performance requirements in practical applications and better meet industrial needs. The most widely used iron-nickel copper is BFe10-1-1 (C70600) and
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BFe30-1-1 (C71500), when the mass fraction of Ni is between 30% and 10%, the alloy has a wider passivation range and the best corrosion resistance. The alloy also has super strong resistance to seawater erosion and corrosion, and is called "marine engineering alloy". The main applications of copper and copper alloys in the field of marine engineering are shown in Table 2.
BFe10-1-1 and BFe30-1-1 alloys have the advantages of good resistance to seawater erosion and corrosion, high heat transfer coefficient, excellent mechanical/welding properties, inhibition of marine microbial adhesion, etc., and are widely used in ship main and auxiliary engines. Cooling water pipes, fire protection pipelines on offshore oil production platforms, heat exchangers in power plants, condensers in coastal nuclear power plants, and brine heaters in multi-stage flash evaporation devices for seawater desalination [2-4]. At the same time, BFe30-1-1 alloy has higher strength and is also used in high-strength structural parts such as shafts, fasteners, valve stems and flanges of some marine devices. The BFe30-2-2 alloy, which is resistant to seawater erosion corrosion and sand corrosion resistance, was developed to deal with the problem of high sand content in seawater in the East China Sea [5]. BFe10-1-1
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The mechanical properties of BFe30-1-1 alloy pipes in the hard state should meet: tensile strength ≥ 370MPa, yield strength ≥ 150MPa, elongation ≥ 18%, Vickers hardness ≥ 85; corrosion resistance: corrosion amount (50℃ , 3.5% NaCl seawater) ≤ 0.025mm/a, no pitting corrosion is allowed. Manganese white copper (BMn3-12 alloy) has a moderate resistance coefficient, a small resistance temperature coefficient and is relatively stable. Due to its good electrical properties, BMn3-12 alloy can be used to make standard resistors and resistive components of other precision instruments. With the development of the times, the requirements for the precision of instruments are getting higher and higher, so the research on this alloy cannot stop at changing the alloy composition and content [6]. Through annealing, horizontal extrusion failure and drawing processes, BMn3-12 alloy has special coherent twin boundaries, which can improve the strength of the material without affecting the conductivity of the material. BMn40-1.5 alloy is an electrical copper-nickel alloy that was used earlier than BMn3-12 alloy. Because of its smaller temperature coefficient of resistance, it has better heat resistance and can be used in a wider temperature range. Compared with BMn3-12 alloy, BMn40-1.5 alloy has a higher thermoelectric potential against copper, so it is suitable for precision resistors, sliding resistors, starting and regulating transformers and resistance strain gauges for AC [8]. Aluminum-nickel copper has both high strength and good plasticity and toughness. Among them, BAl13-3 alloy is often used to make higher-strength corrosion-resistant parts, and BAl16-1.5 alloy is used to make flat springs with important uses. For a long time, in order to improve the performance of aluminum-nickel copper, a small amount of trace elements are often added to create a strengthened matrix of aluminum-nickel copper, which has good conductivity while maintaining high strength to meet practical application requirements. Because aluminum-nickel copper has high strength, high electrical conductivity and good wear resistance, it can be used as a potential material for lead frames and wear-resistant parts [9-11].
Zinc cupronickel (BZn18-18BZn15-20 alloy) is also called "German silver" [12]. Because zinc-nickel copper has the advantages of good tensile strength, fatigue resistance and corrosion resistance, it is mainly used as shells of components or crystals, medical equipment, construction materials, and wind instrument shells [13].
3. Copper-nickel alloy performance requirements
With the rapid development of my country's marine shipbuilding industry, offshore oil and gas industry, marine mining, marine power and seawater desalination industries, the requirements for materials are becoming higher and higher [16]. Among them, copper-nickel alloy pipes are mostly used. Copper alloy condenser pipes for ships have long been working in high temperature, high pressure and highly corrosive cooling medium - seawater environment. Therefore, it is no longer enough for the chemical composition, mechanical properties, and seawater corrosion resistance of the product to meet the requirements. Strict requirements must also be placed on geometric dimensional accuracy, process performance, internal organization and other indicators. At the same time, copper-nickel alloy pipes are also required to have good corrosion resistance. , high heat transfer coefficient, large diameter, high precision, excellent mechanical welding technology, and good ability to inhibit the adhesion of marine microorganisms [17] and other characteristics. At present, due to problems with processing equipment in China, large-diameter copper tube alloys are still unable to be mass-produced and mainly rely on foreign imports. Therefore, the production difficulties of large-diameter copper pipes still need to be overcome.
4. Research progress of copper-nickel alloys
4.1 Corrosion mechanism of copper-nickel alloy
Figure 4 shows the various processes of the corrosion reaction of cupronickel in oxygenated seawater. The AB line in the figure is the cathode reaction process of cupronickel in seawater, which can be expressed as:
1/2[O2]+[H2O]+2e−=2[OH−] (1)
The CD line in Figure 4 is the anode reaction process of white copper without passivation in seawater. It can be expressed as:
Cu=Cu++e−(2)
T1, T2, T3 in Figure 4
The curve is the anodic reaction process of passivation of white copper in seawater. The EF line is a hydrogen evolution reaction process of white copper due to lack of oxygen, so neither passivation nor corrosion products are formed during this process.
Cu(orCu2O)=Cu2++2e−(3)
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2[Cu2+]+3[OH−]+[Cl−]=Cu2(OH)3Cl (4)
4.2 Research on corrosion resistance of copper-nickel alloy
In order to meet the performance requirements of marine industry materials, a lot of research has been done to improve the corrosion resistance of copper-nickel alloys. Deng Chuping[19] found that the tensile strength and elongation of white copper added with rare earth Ce were improved, and the grain structure was denser. Moreover, adding rare earth Ce could improve the typical denickel corrosion of the alloy in sulfur-containing media. tendency. Jiang et al. [20] studied the effects of different Fe contents on the structure and properties of B10 alloy, and found that as the Fe content increased, the corrosion resistance showed a trend of first increasing and then decreasing, but did not further explore the corrosion resistance mechanism. Research. Beijing Nonferrous Metals Research Institute
Zhang Jianing [21] found the best alloy ratio to improve the corrosion resistance of B10 by controlling the Fe/Mn ratio. The study found that when Fe/Mn=3:2, the corrosion resistance of the alloy is the best. Ma et al. [22] of the Chinese Academy of Sciences found that the use of solid solution + cold rolling deformation + recrystallization annealing process can increase the number of grain boundaries and twin boundaries, thereby obtaining an alloy with better corrosion resistance.
5 Conclusion
This article mainly takes copper-nickel alloy as the starting point, explains the chemical composition and application scenarios of different copper-nickel alloys, introduces the leading copper condenser tube production factories at home and abroad, and the performance of copper-nickel alloy tubes for domestic marine system pipelines. demand and future trends in the development of copper-nickel alloys. The main research progress of copper-nickel alloys is summarized. At present, the main progress is from adding trace amounts of rare earth elements to adding different contents.
Fe element, changing the ratio of matrix alloy elements and grain boundary engineering to improve the corrosion resistance of copper-nickel alloys.
