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Today we come to learn about nickel-based alloys.
Nickel-based alloys are divided into nickel-based heat-resistant alloys, nickel-based corrosion-resistant alloys, nickel-based wear-resistant alloys, nickel-based precision alloys, and nickel-based shape memory alloys. High-temperature alloys are divided into iron-based superalloys, nickel-based superalloys and cobalt-based superalloys according to the different substrates. We have to talk about nickel first. Like iron and copper, nickel has been used in alloys since it entered civilized society. But compared with steel, brass and bronze, nickel alloys are latecomers to the chemical industry. With the continuous progress of metallurgical technology and manufacturing technology, the development of nickel alloys has been promoted, and their wide application in the chemical industry has been promoted. Nickel alloy combines excellent corrosion resistance, strength, toughness, metallurgical stability, workability and weldability. Many nickel alloys also have excellent heat resistance and are ideal for applications requiring high temperature strength and chemical resistance at high temperatures.
In addition to nickel, the roles of various elements in nickel-based alloys are as follows:
1. The role of boron and silicon elements: significantly reduce the melting point of the alloy, expand the temperature range of the solid-liquid line, and form a low-melting eutectic; deoxidation and reduction and slagging functions; hardening and strengthening of the coating; improving the performance of the operation process.
2. The role of copper element: improve the corrosion resistance to non-oxidizing acids.
3. The role of chromium: solid solution strengthening and passivation; improving corrosion resistance and high temperature oxidation resistance; excess chromium is easy to form chromium carbide and chromium boride hard phases with carbon and boron to improve alloy hardness and resistance Abrasive.
4. The role of molybdenum element: large atomic radius, large distortion of the crystal lattice after solid solution, significantly strengthen the alloy matrix, improve the high temperature strength and red hardness of the matrix; it can cut off and reduce the network structure in the coating; improve the resistance Cavitation and erosion ability nickel-based precision alloy.
The first commercially important nickel alloy was Alloy 400, which was developed by the International Nickel Company (later called Inco Alloy Company) in 1905 and introduced to the market under the trademark MONEL. The next important milestone was the nickel-molybdenum alloy B and nickel-chromium-molybdenum-tungsten alloy C, which came out around 1930. Their inventor is Haynes Stellite (now called Haynes International), two of which are registered trademarks HASTELLOY.
The composition and performance of nickel-based superalloys are okay.
Nickel-based superalloys are most widely used. The main reason is that, one is that more alloying elements can be dissolved in the nickel-based alloy, and it can maintain good structural stability; the other is that it can form a coherent and ordered A3B-type intermetallic compound γ[Ni3(Al, Ti)] As a strengthening phase, the alloy can be effectively strengthened and obtain higher high temperature strength than iron-based superalloys and cobalt-based superalloys; thirdly, nickel-based alloys containing chromium have better oxidation and resistance than iron-based superalloys. Gas corrosion ability. Nickel-based superalloys have solid solution strengthened alloys and precipitation strengthened alloys according to their strengthening methods.
Smelting: In order to obtain more pure molten steel, reduce the gas content and the content of harmful elements; at the same time, due to the presence of easily oxidizable elements such as Al and Ti in some alloys, it is difficult to control non-vacuum smelting; it is also to obtain better thermoplasticity , Nickel-based heat-resistant alloys are usually smelted in a vacuum induction furnace, and even produced by vacuum induction smelting plus vacuum consumable furnace or electroslag furnace remelting.
In terms of deformation: forging and rolling processes are used. For alloys with poor thermoplasticity, they are even rolled after extrusion and billeting or are directly extruded with mild steel (or stainless steel) sheathing. The purpose of deformation is to break the casting structure and optimize the microstructure.
Casting: usually use vacuum induction furnace to smelt the master alloy to ensure the composition and control the gas and impurity content, and use the vacuum remelting-precision casting method to make parts.
Heat treatment: Wrought alloy and some cast alloys need to be heat treated, including solution treatment, intermediate treatment and aging treatment. Take Udmet 500 alloy as an example. Its heat treatment system is divided into four stages: solution treatment, 1175℃, 2 hours, Air cooling; intermediate treatment, 1080°C, 4 hours, air cooling; primary aging treatment, 843°C, 24 hours, air cooling; secondary aging treatment, 760°C, 16 hours, air cooling. In order to obtain the required organizational state and good overall performance.
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