What Is Nickel Based Alloy

Nickel based alloys refer to a type of alloy that has high strength and certain resistance to oxidation and corrosion at high temperatures of 650-1000 ℃. According to their main properties, they 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 high-temperature alloys, nickel based high-temperature alloys, and cobalt based high-temperature alloys according to their different substrates. Nickel based high-temperature alloys are commonly referred to as nickel based alloys.

Representative materials of nickel based alloys include:

1. Incoloy alloys, such as Incoloy800, mainly consist of:; 32Ni-21Cr Ti, Al; belongs to heat-resistant alloys;

2. Inconel alloys, such as Inconel600, mainly consist of:; 73Ni-15Cr-Ti, Al; belongs to heat-resistant alloys;

3. Hastelloy alloy, also known as Hastelloy alloy, such as Hastelloy C-276, mainly consists of:; 56Ni-16Cr-16Mo-4W； Belonging to corrosion-resistant alloys;

4. Monel alloy, also known as Monel alloy, such as Monel 400, has the following main components:; 65Ni-34Cu； Belonging to corrosion-resistant alloys;

The main alloying elements include chromium, tungsten, molybdenum, cobalt, aluminum, titanium, boron, zirconium, etc. Among them, Cr, Ai and other elements mainly play an antioxidant role, while other elements have solid solution strengthening, precipitation strengthening, and grain boundary strengthening effects.

It has high strength and certain anti-oxidation and corrosion resistance at high temperatures of 650-1000 ℃. Due to its sufficiently high high-temperature strength and anti-oxidation and corrosion resistance, it is commonly used in the manufacture of high-temperature components for aircraft engine blades, rocket engines, nuclear reactors, and energy conversion equipment.

Development history

Nickel based high-temperature alloys (hereinafter referred to as nickel based alloys) were developed in the late 1930s. The UK first produced nickel based alloy Nimonic 75 (Ni-20Cr-0.4Ti) in 1941; In order to improve creep strength and add aluminum, Nimonic 80 (Ni-20Cr-2.5Ti-1.3Al) was developed. The United States developed nickel based alloys in the mid-1940s, the Soviet Union in the late 1940s, and China in the mid-1950s. The development of nickel based alloys includes two aspects: the improvement of alloy composition and the innovation of production processes. In the early 1950s, the development of vacuum melting technology created conditions for refining nickel based alloys containing high aluminum and titanium. Most of the early nickel based alloys were deformation alloys. In the late 1950s, due to the increase in working temperature of turbine blades, alloys were required to have higher high-temperature strength. However, as the strength of the alloy increased, it became difficult or even impossible to deform. Therefore, investment casting precision casting technology was adopted to develop a series of casting alloys with good high-temperature strength. In the mid-1960s, directional crystallization and single crystal high-temperature alloys with better performance, as well as powder metallurgy high-temperature alloys, were developed. In order to meet the needs of ships and industrial gas turbines, a batch of high chromium nickel based alloys with good thermal corrosion resistance and stable structure have been developed since the 1960s. During approximately 40 years from the early 1940s to the late 1970s, the operating temperature of nickel based alloys increased from 700 ℃ to 1100 ℃, with an average annual increase of about 10 ℃.

Composition and Performance

Nickel based high-temperature alloys are the most widely used. The main reason is that nickel based alloys can dissolve more alloying elements and maintain good structural stability; Secondly, it can form a coherent ordered A3B type intermetallic compound γ [Ni3 (Al, Ti)] phase as a strengthening phase, effectively strengthening the alloy and achieving higher high-temperature strength than iron-based high-temperature alloys and cobalt based high-temperature alloys; Thirdly, nickel based alloys containing chromium have better oxidation resistance and gas corrosion resistance than iron-based high-temperature alloys. Nickel based alloys contain more than ten elements, among which Cr mainly plays a role in oxidation and corrosion resistance, while other elements mainly play a strengthening role. According to their strengthening mechanisms, they can be divided into solid solution strengthening elements such as tungsten, molybdenum, cobalt, chromium, and vanadium; Precipitation strengthening elements such as aluminum, titanium, niobium, and tantalum; Grain boundary strengthening elements such as boron, zirconium, magnesium, and rare earth elements.

Nickel based high-temperature alloys can be strengthened by solid solution strengthening and precipitation strengthening methods.

Production process

In terms of smelting: in order to obtain purer and purified molten steel, reduce gas content and harmful element content; Meanwhile, due to the presence of easily oxidizable elements such as Al and Ti in some alloys, non vacuum smelting is difficult to control; In order to achieve better thermoplasticity, nickel based heat-resistant alloys are usually melted in vacuum induction furnaces, and even produced by vacuum induction melting combined with vacuum consumable furnaces or electric slag furnaces for remelting.

In terms of deformation, forging and rolling processes are adopted, and for alloys with poor thermoplasticity, extrusion and rolling after billet opening or direct extrusion process with soft steel (or stainless steel) cladding is even used. The purpose of deformation is to break the casting structure and optimize the microstructure.

In terms of casting, the mother alloy is usually melted in a vacuum induction furnace to ensure composition and control gas and impurity content, and the parts are produced by vacuum remelting precision casting method.

In terms of heat treatment, deformed alloys and some cast alloys require heat treatment, including solution treatment, intermediate treatment, and aging treatment. Taking 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 ℃, 4 hours, air cooling; One time aging treatment, 843 ℃, 24 hours, air cooling; Secondary aging treatment, 760 ℃, 16 hours, air cooling. To achieve the required organizational status and good overall performance.

Ni-base corrosion resistant alloy

The main alloying elements are copper, chromium, and molybdenum. Has good comprehensive performance and can withstand 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) alloys (also known as nickel based heat-resistant alloys and corrosion-resistant alloys), nickel molybdenum (Ni Mo) alloys (mainly referring to Hastelloy B series, with professional corrosion-resistant alloy production companies including Beijing Iron and Steel Research Institute, Shanghai Kangsheng Special Alloy Co., Ltd., Beijing Rongpin Technology Co., Ltd., Baotai Group Rare Metal Materials Co., Ltd.), nickel chromium molybdenum (Ni Cr Mo) alloys (mainly referring to Hastelloy C series, with professional corrosion-resistant alloy production companies including Beijing Iron and Steel Research Institute, Beijing Rongpin Technology Co., Ltd., Baotai Group Rare Metal Materials Co., Ltd.), 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 in the manufacturing of various corrosion-resistant environmental components such as petroleum, chemical, and power.

Category: Nickel based corrosion-resistant alloys often have austenitic structures. In the solid solution and aging treatment states, there are still intermetallic phases and metal carbonitrides present on the austenite matrix and grain boundaries of the alloy. Various corrosion-resistant alloys are classified by composition and their characteristics are as follows.

Ni Cu alloy: It 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 resistance to fluorine gas, hydrogen fluoride, and hydrofluoric acid under anaerobic and oxidizing conditions (see metal corrosion).

Ni Cr alloy: also known as nickel based heat-resistant alloy; Mainly used under oxidative medium conditions. Its resistance to high temperature oxidation and corrosion by gases containing sulfur, vanadium, etc. increases with the increase of chromium content. This type of alloy also has good resistance to corrosion by hydroxides (such as NaOH, KOH) and stress corrosion.

Ni Mo alloy: mainly used under corrosive conditions in reducing media. It is the best alloy resistant to hydrochloric acid corrosion, but its corrosion resistance significantly decreases in the presence of oxygen and oxidants.

Ni Cr Mo (W) alloy: It combines the properties of the aforementioned Ni Cr and Ni Mo alloys. Mainly used under conditions of oxidation-reduction mixed media. This type of alloy has good corrosion resistance in high-temperature hydrogen fluoride, hydrochloric acid and hydrofluoric acid solutions containing oxygen and oxidants, and wet chlorine gas at room temperature.

Ni Cr Mo Cu alloy: It has the ability to resist both nitric acid and sulfuric acid corrosion, and also has good corrosion resistance in some oxidation-reduction mixed acids.

Nickel based wear-resistant alloy

The main alloying elements are chromium, molybdenum, tungsten, and also contain small amounts of niobium, tantalum, and indium. In addition to its wear resistance, it also has good oxidation resistance, corrosion resistance, and welding performance. It can be used to manufacture wear-resistant components and also as a coating material, which can be coated on the surface of other substrate materials through welding and spraying processes.

The main alloying elements are chromium, molybdenum, tungsten, and also contain small amounts of niobium, tantalum, and indium. In addition to its wear resistance, it also has good oxidation resistance, corrosion resistance, and welding performance. It can be used to manufacture wear-resistant components and also as a coating material, which can be coated on the surface of other substrate materials through welding and spraying processes.

Nickel based alloy powders include self melting alloy powders and non self melting alloy powders.

Non self melting nickel based powder refers to nickel based alloy powder that does not contain B, Si, or has low B and Si content. This type of powder is widely used in plasma arc spraying coatings, flame spraying coatings, and plasma surface strengthening. Mainly including: 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 an appropriate amount of B and Si to nickel alloy powder forms nickel based self melting alloy powder. The so-called self melting alloy powder, also known as low melting point alloy or hard surface alloy, is a series of powder materials formed by adding alloy elements (mainly boron and silicon) that can form low melting point eutectic in nickel, cobalt, and iron-based alloys. The commonly used nickel based self melting 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 melting alloy powder, high chromium molybdenum nickel based self melting alloy powder, Ni-Cr-W-C based self melting alloy powder, high copper self melting alloy powder, tungsten carbide dispersed nickel based self melting alloy powder, etc.

Nickel based shape memory alloy

Nickel alloy containing 50 (at)% titanium. Its recovery temperature is 70 ℃, and its shape memory effect is good. A small change in the nickel titanium composition ratio can cause the recovery temperature to vary within the range of 30-100 ℃. It is commonly used in the manufacturing of automatic opening structural components for spacecraft, self-excited fasteners for aerospace industry, and artificial heart motors for biomedical applications.

The role of various elements in alloys

The role of boron and silicon elements: significantly reducing the melting point of alloys, expanding the solid-liquid phase line temperature range, and forming low melting eutectic; Deoxygenation reduction and slagging function; The hardening and strengthening effect on the coating; Improve operational process performance.

The function of copper element: to enhance its corrosion resistance to non oxidizing acids.

The role of chromium element: solid solution strengthening effect, passivation effect; Improve corrosion resistance and high temperature oxidation resistance; Excess chromium easily forms hard phases of chromium carbide and chromium boride with carbon and boron, thereby improving the hardness and wear resistance of the alloy.

The role of molybdenum element: With a large atomic radius, it causes significant lattice distortion after solid solution, significantly strengthening the alloy matrix and improving its high-temperature strength and red hardness; Can cut and reduce the mesh structure in the coating; Improve the resistance to cavitation and erosion of nickel based precision alloys.

Including nickel based soft magnetic alloys, nickel based precision resistance alloys, and nickel based electric heating alloys.

The most commonly used soft magnetic alloy is BOMO alloy containing about 80% nickel, which has high maximum and initial magnetic 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 electrical resistivity, low temperature coefficient of resistivity, and good corrosion resistance, and is used to make resistors. Nickel based electric heating alloy is a nickel alloy containing 20% chromium, which has good oxidation and corrosion resistance and can be used for a long time at temperatures of 1000-1100 ℃.