Composition performance
Nickel-based superalloys are the most widely used. The main reason is that, firstly, more alloying elements can be dissolved in the nickel-based alloy, and better structure stability can be maintained; secondly, a coherent and ordered A3B type intermetallic compound γ[Ni3(Al, Ti)] can be formed As a strengthening phase, the alloy can be effectively strengthened and obtain higher high-temperature strength than iron-based superalloys and cobalt-based superalloys; third, 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 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.
Nickel-based superalloys have solid solution strengthening alloys and precipitation strengthening alloys according to their strengthening methods.
Production Process
Smelting: In order to obtain more pure molten steel, reduce the gas content and the content of harmful elements; at the same time, due to the presence of easily oxidizable elements such as Al and Ti in some alloys, it is difficult to control non-vacuum smelting; it is also to obtain better thermoplasticity , Nickel-based heat-resistant alloys are usually smelted in a vacuum induction furnace, and even produced by vacuum induction smelting plus vacuum consumable furnace or electroslag furnace remelting.
In terms of deformation: forging and rolling processes are used. For alloys with poor thermoplasticity, they are even rolled after extrusion and billeting or are directly covered with mild steel (or stainless steel). The purpose of deformation is to break the casting structure and optimize the microstructure.
Casting: usually use vacuum induction furnace to smelt master alloy to ensure composition and control gas and impurity content, and use vacuum remelting-precision casting method to make parts.
Heat treatment: Wrought alloy and some cast alloys need to be heat treated, including solution treatment, intermediate treatment and aging treatment. Take 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°C, 4 hours, air cooling; primary aging treatment, 843°C, 24 hours, air cooling; secondary aging treatment, 760°C, 16 hours, air cooling. In order to obtain the required organizational state and good overall performance.