Nickel Base Alloy Type
The main alloying elements are copper, chromium, and molybdenum. They have good comprehensive properties and are resistant to various acid corrosion and stress corrosion. The earliest application (produced in the United States in 1905) was nickel-copper (Ni-Cu) alloy, also known as Monel alloy (Monel alloy Ni 70 Cu30); in addition, there are nickel-chromium (Ni-Cr) alloy (that is, nickel-based heat-resistant alloy, heat-resistant corrosion alloy in corrosion-resistant alloy), nickel-molybdenum (Ni-Mo) alloy (mainly Hastelloy B series), nickel-chromium-molybdenum (Ni-Cr-Mo) alloy (mainly Hastelloy C series), etc. At the same time, pure nickel is also a typical representative of nickel-based corrosion-resistant alloys. These nickel-based corrosion-resistant alloys are mainly used to manufacture various corrosion-resistant environment parts such as petroleum, chemical industry, and electric power.
Nickel-based corrosion-resistant alloys mostly have austenitic structure. In the state of solid solution and aging treatment, there are intermetallic phases and metal carbonitrides in the austenite matrix and grain boundaries of the alloy. The various corrosion-resistant alloys are classified by composition and their characteristics as follows:
Ni-Cu alloy has better corrosion resistance than nickel in reducing media, and better corrosion resistance than copper in oxidizing media. It is the best material for high-temperature fluorine gas, hydrogen fluoride and hydrofluoric acid in the absence of oxygen and oxidants.
Ni-Cr alloy is also a nickel-based heat-resistant alloy; it is mainly used in oxidizing media. It is resistant to high-temperature oxidation and corrosion by gases containing sulfur, vanadium, etc., and its corrosion resistance increases with the increase of chromium content. This type of alloy also has good resistance to hydroxide corrosion (such as NaOH, KOH) and stress corrosion.
Ni-Mo alloy is mainly used under conditions of reducing medium corrosion. It is the best alloy for hydrochloric acid corrosion resistance, but its corrosion resistance will decrease significantly in the presence of oxygen and oxidants.
Ni-Cr-Mo(W) alloy has the properties of the above-mentioned Ni-Cr alloy and Ni-Mo alloy. Mainly used in oxidation-reduction mixed medium conditions. This type of alloy has good corrosion resistance in high-temperature hydrogen fluoride gas, hydrochloric acid and hydrofluoric acid solutions containing oxygen and oxidants, and wet chlorine gas at room temperature.
Ni-Cr-Mo-Cu alloy has the ability to resist both nitric acid and sulfuric acid corrosion, and also has good corrosion resistance in some oxidation-reduction mixed acids.
The main alloying elements are chromium, molybdenum, tungsten, and also contain a small amount of niobium, tantalum and indium. In addition to wear resistance, it also has good oxidation resistance, corrosion resistance and welding performance. It can be used to manufacture wear-resistant parts, and can also be used as a coating material, which can be coated on the surface of other base materials through surfacing and spraying processes.
Nickel-based alloy powders include self-fluxing alloy powders and non-self-fluxing alloy powders.
Non-self-fluxing nickel-based powders refer to nickel-based alloy powders that do not contain B, Si or have a low content of B and Si. This type of powder is widely used in plasma arc spray coatings, flame spray coatings and plasma surface strengthening. Mainly include: Ni-Cr alloy powder, Ni-Cr-Mo alloy powder, Ni-Cr-Fe alloy powder, Ni-Cu alloy powder, Ni-P and Ni-Cr-P alloy powder, Ni-Cr-Mo-Fe alloy powder, Ni-Cr-Mo-Si high wear-resistant alloy powder, Ni-Cr-Fe-Al alloy powder, Ni-Cr-Fe-Al-B-Si alloy powder, Ni-Cr-Si alloy powder, Ni-Cr-W based wear-resistant and corrosion-resistant alloy powder, etc.
Adding appropriate amount of B and Si to nickel alloy powder forms nickel-based self-fluxing alloy powder. The so-called self-fluxing alloy powder is also called low eutectic alloy, hard-facing alloy, which is a series of powder materials formed by adding alloying elements (mainly boron and silicon) that can form low melting point eutectic to nickel, cobalt and iron-based alloys. Commonly used nickel-based self-fluxing alloy powders include Ni-B-Si alloy powder, Ni-Cr-B-Si alloy powder, Ni-Cr-B-Si-Mo, Ni-Cr-B-Si-Mo-Cu, high-molybdenum nickel-based self-fluxing alloy powder, high-chromium-molybdenum nickel-based self-fluxing alloy powder, Ni-Cr-W-C-based self-fluxing alloy powder, high-copper self-fluxing alloy powder, tungsten carbide dispersion type nickel-based self-fluxing alloy powder, etc.
The role of various elements in the alloy:
● The role of boron and silicon: significantly reduce the melting point of the alloy, expand the solid-liquid phase temperature zone, and form a low-melting eutectic; deoxidation reduction and slag-making functions; hardening and strengthening of the coating; improve the operating process performance
● The role of copper: improve the corrosion resistance to non-oxidizing acids
● The role of chromium: solid solution strengthening and passivation; improve corrosion resistance and high-temperature oxidation resistance; excess chromium easily forms chromium carbide and chromium boride hard phases with carbon and boron to improve the hardness and wear resistance of the alloy
● The role of molybdenum: large atomic radius, large lattice distortion after solid solution, significantly strengthen the alloy matrix, improve the high-temperature strength and red hardness of the matrix; can cut and reduce the network structure in the coating; improve the ability to resist cavitation and erosion.
Include nickel-based soft magnetic alloys, nickel-based precision resistance alloys and nickel-based electric heating alloys. The most commonly used soft magnetic alloy is Permalloy, which contains about 80% nickel. It has high maximum permeability and initial permeability, low coercivity, and is an important iron core material in the electronics industry. The main alloying elements of nickel-based precision resistance alloys are chromium, aluminum, and copper. This alloy has high resistivity, low resistivity temperature coefficient, and good corrosion resistance, and is used to make resistors. Nickel-based electric heating alloy is a nickel alloy containing 20% chromium. It has good oxidation resistance and corrosion resistance and can be used for a long time at 1000-1100℃.
A nickel alloy containing 50 (at)% titanium. Its recovery temperature is 70°C and has a good shape memory effect. By slightly changing the ratio of nickel and titanium, the recovery temperature can be changed within the range of 30 to 100°C. It is mostly used to manufacture automatically opening structural parts used on spacecraft, self-exciting fasteners used in the aerospace industry, and artificial heart motors used in biomedicine.
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