All kinds of degradation rates of materials are accelerated under high temperature environment. In the process of use, it is easy to cause organizational instability, deformation and crack growth under the effect of temperature and stress, and oxidation corrosion of material surface.
1. High temperature and corrosion resistance
The high temperature resistance and corrosion resistance of superalloy mainly depend on its chemical composition and structure. Taking GH4169 nickel base deformed superalloy as an example, it can be seen that the content of niobium in GH4169 alloy is high, and the degree of niobium segregation in the alloy is directly related to the metallurgical process. The GH4169 matrix is a Ni Gr solid solution, which can withstand a high temperature of about 1000 ℃ when the mass fraction of Ni is more than 50%, similar to the American brand Inconel 718. The alloy consists of γ Matrix phase δ Phase, carbide and strengthening phase γ' and γ″ Phase composition. 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 construct its excellent mechanical properties.
2. High processing difficulty
Because of the complex and harsh working environment of superalloy, its machined surface integrity plays a very important role in its performance. However, superalloys are typical difficult to machine materials. Their micro hardening items have high hardness, severe work hardening, high resistance to shear stress and low thermal conductivity, and high cutting force and cutting temperature in the cutting area. In the process of machining, problems such as low machining surface quality and very serious tool damage often occur. Under general cutting conditions, the surface layer of superalloy will produce excessive hardening layer, residual stress, white layer, black layer, grain deformation layer, etc.