Superalloys are key materials in the manufacture of aviation, aerospace, ship engines and gas turbines for thermal power plants. Taking aero-engine as an example, it is the key to improve and improve the performance level of the engine to improve the air inlet temperature, increase the thrust-to-weight ratio, reduce the engine weight, and improve the safety and durability of the engine. The realization of these goals depends directly on the production and use of superalloys with excellent microstructure and properties. Among a wide variety of superalloys, niobium as the main strengthening element plays an important role. This kind of alloy can precipitate out a large number of "(Ni3Nb) phase with higher coherent stress with the matrix, and the strengthening effect is significant, so it has the characteristics of high strength.
As a representative of high niobium reinforced superalloys, IN718 alloys can be used in both as-cast and morphologic conditions. Compared with the variable shape IN718 alloy, the cast IN718 alloy has a lower strength, but it can avoid the low strength points caused by welding or various connections, and it also has the advantage of being hard to replace for the abnormity parts. Various attempts have been made to improve the performance of IN718 alloy castings. For example, the rapid solidification method is used to refine the grain structure of the cast IN718 alloy to improve the strength and toughness of the alloy. However, rapid solidification leads to a large number of voids in the alloy castings, which has harmful effects on the performance of the alloy castings. In order to eliminate these defects in the casting process of cavity, the alloy casting hot isostatic pressing technology is adopted for processing, although hot isostatic pressing treatment can make the hole closed, but usually need to retain some casting polycrystalline IN718 alloy Laves phase as a strengthening phase at grain boundaries, so you can't eliminate dendritic dry and interdendritic segregation. In addition, the Nb content of Laves phase is relatively high, so the retention of part of Laves phase must reduce the content of "Ni3Nb enhanced phase. Therefore, the strength potential of IN718 alloy cannot be fully developed. Other high niobium enhanced alloys, such as Inconel 625 and Inconel 725, have about 3.5wt. % Niobium content and serious segregation tendency. Therefore, how to eliminate the solidification segregation of high niobium alloy is the key to give full play to the performance potential of this alloy.
It can be seen that by using the special heat treatment system of the invention, the tensile strength of K718 alloy at room temperature has been greatly improved, the yield strength has been increased by 189.1mpa, the fracture strength has been increased by 347MPa and the plasticity has also been improved to some extent.
