Development and Application of Nickel-Based Superalloys
High-temperature alloy refers to a type of metal material based on iron, nickel, and cobalt that can work for a long time at a high temperature above 600°C and certain stress. And has high-temperature strength, good oxidation and corrosion resistance, good fatigue performance, fracture toughness, and other comprehensive properties. The superalloy is a single austenitic structure, which has good structure stability and service reliability at various temperatures. Then, the high-temperature alloy with nickel as the matrix (the content is generally greater than 50%) in the range of 650-1000℃ has high strength and good oxidation resistance, and gas corrosion resistance is called nickel-based superalloy (hereinafter referred to as “nickel Base alloy”).
The development of nickel-based superalloys includes two aspects: the improvement of alloy composition and the innovation of production technology. Nickel-based superalloys were developed in the late 1930s. Britain first produced nickel-based superalloy Nimonic 75 (Ni-20Cr-0.4Ti) in 1941; in order to increase the creep strength, aluminum was added, and Nimonic 80 (Ni-20Cr-2.5Ti-1.3Al) was developed. The United States in the mid-1940s, the Soviet Union in the late 1940s, and China in the mid-1950s also developed nickel-based alloys. 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 superalloys were deformed alloys.
In the late 1950s, due to the increase in the working temperature of turbine blades, alloys were required to have higher high-temperature strength. However, when the strength of the alloy was high, it was difficult to deform or even unable to deform. Therefore, investment casting technology was used to develop a series of excellent Cast alloys with high-temperature strength. In the mid-1960s, oriented crystallization and single crystal superalloys and powder metallurgy superalloys with better performance were developed.
In order to meet the needs of ships and industrial gas turbines, a number of high-chromium nickel-based alloys with better thermal corrosion resistance and stable structure have been developed since the 1960s. In about 40 years from the early 1940s to the late 1970s, the working temperature of nickel-based superalloys increased from 700°C to 1100°C, an average annual increase of about 10°C.
Nickel-based superalloys are the most widely used and the highest high-temperature strength alloys in superalloys. The main reason is that more alloying elements can be dissolved in the nickel-based alloy and the structural stability can be maintained; the second is that it can form a coherent and ordered A3B type intermetallic compound g [Ni3(Al, Ti)]
As a strengthening phase, the alloy is effectively strengthened to 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 alloys contain more than ten elements, of which Cr mainly plays an anti-oxidation and anti-corrosion role, and other elements mainly play a strengthening role.
According to their strengthening action mode, 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, etc. According to the strengthening method of nickel-based alloys, there are solid solution strengthened alloys and precipitation strengthened alloys.