Definition and Properties for High Temperature Alloy

High temperature alloy definition

High-temperature alloy refers to a type of metal material based on iron, nickel, and cobalt that can work at high temperatures above 600°C and under certain stress for a long time; and has high high-temperature strength, good anti-oxidation and anti-corrosion properties, Good fatigue performance, fracture toughness and other comprehensive properties. High-temperature alloys have a single austenite structure and have good structural stability and service reliability at various temperatures.

Based on the above performance characteristics and the high degree of alloying of high-temperature alloys, they are also called "superalloys" and are an important material widely used in aviation, aerospace, petroleum, chemical industry, and ships. According to the matrix elements, high-temperature alloys are divided into iron-based, nickel-based, cobalt-based and other high-temperature alloys. The service temperature of iron-based high-temperature alloys can generally only reach 750~780°C. For heat-resistant parts used at higher temperatures, nickel-based and refractory metal-based alloys are used. Nickel-based high-temperature alloys occupy a particularly important position in the entire field of high-temperature alloys. They are widely used to manufacture the hottest components of aviation jet engines and various industrial gas turbines.

High temperature alloy properties

Various degradation rates of materials are accelerated in high-temperature environments. During use, tissue instability, deformation and crack growth under the action of temperature and stress, and oxidative corrosion of the material surface are prone to occur.

1.High temperature resistance and corrosion resistance

The high temperature resistance, corrosion resistance and other properties of high temperature alloys mainly depend on its chemical composition and organizational structure. Taking the GH4169 nickel-based deformed high-temperature alloy as an example, it can be seen that the niobium content in the GH4169 alloy is high, and the niobium segregation in the alloy is directly related to the metallurgical process. The matrix of GH4169 is Ni-Gr solid solution, and the mass fraction of Ni containing more than 50% can be tolerated. At a high temperature of about 1 000°C, it is similar to the American brand Inconel718. The alloy is composed of γ matrix phase, δ phase, carbide and strengthening phase γ' and γ″ phases. The chemical elements and matrix structure of GH4169 alloy show its strong mechanical properties. The yield strength and tensile strength are several times better than 45 steel, and the plasticity is also better than 45 steel. The stable lattice structure and a large number of strengthening factors contribute to its excellent mechanical properties.

2.High processing difficulty

Due to its complex and harsh working environment, the integrity of the processed surface of high-temperature alloys plays a very important role in its performance. However, high-temperature alloys are typically difficult-to-machine materials. They have high microhardness, severe work hardening, high resistance to shear stress and low thermal conductivity. The cutting force and cutting temperature in the cutting area are high, which often occurs during processing. The machined surface quality is low and the tool is severely damaged. Under normal cutting conditions, the surface layer of high-temperature alloy will produce excessive problems such as hardened layer, residual stress, white layer, black layer, and grain deformation layer.