Casting high temperature alloys

High-temperature alloy materials for which parts are prepared directly by casting methods. According to the alloy matrix composition, it can be divided into 3 types of iron-based casting high-temperature alloys, nickel-based casting high-temperature alloys and cobalt-based casting high-temperature alloys

Cast superalloy
High-temperature alloy materials that are prepared directly from parts by casting method. According to the alloy matrix composition, it can be divided into three types of iron-based cast superalloy, nickel-based cast superalloy and drill-based cast superalloy. According to the crystallization method, it can be divided into 4 types, such as polycrystalline casting high temperature alloy, directional solidification casting high temperature alloy, directional eutectic casting high temperature alloy and single crystal casting high temperature alloy. Most of the casting high-temperature alloys belong to polycrystalline casting high-temperature alloys.

Features Casting high-temperature alloys have the following characteristics.
(1) high degree of alloying. γ' strengthening phase (see high temperature alloy materials metal ask compound phase) formation elements such as aluminum, titanium, niobium, tantalum up to 16%, but also add a certain amount of solid solution strengthening elements tungsten, molybdenum.
(2) Chromium content is low, most are below 10%.
(3) grain boundary strengthening elements boron content are in the O.01% or more.
(4) Most of the carbon content is more than O.1%, some of the carbon content of cobalt-based cast high-temperature alloys up to 1%. (5) Some casting high-temperature alloys are added 1% to 2% hafnium, to improve mid-temperature plasticity, and improve creep strength.
Microstructure characteristics Casting high temperature alloy microstructure (see high temperature alloy material microstructure), in addition to γ' phase, there are γ- γ' eutectic phase, primary carbide phase is also more, along the dendritic intergranular distribution, some alloys and M3B2 boride precipitation. Casting high temperature alloy heat treatment process is relatively simple, and some even do not need to heat treatment can be used.

Casting high-temperature alloys are generally smelted in a large vacuum induction furnace to produce the master alloy, and then remelted and cast into parts in a small vacuum induction furnace using the lost wax precision molding method.
Defects and elimination Casting parts will inevitably produce some microscopic sparse, can be used to reduce or eliminate the hot isostatic treatment, increasing the reliability of the parts. Casting high-temperature alloy parts have a relatively large grain size, which is detrimental to fatigue performance. The surface grain refinement method is usually used to obtain the surface layer of the part fine crystal.
Development direction The use of directional solidification technology can produce no transverse grain boundary of the columnar crystal blade or completely eliminate the grain boundary of the single crystal blade, so that high temperature fatigue life and lasting strength are multiplied, which is the current development direction of casting high temperature alloy.