Preparation Process

1. Foundry metallurgical process

Various advanced casting manufacturing technologies and processing equipment are constantly being developed and improved, such as thermal control solidification, fine-grain technology, laser forming repair technology, wear-resistant casting casting technology, etc. The original technical level is constantly improved to improve various high-temperature alloy castings Product quality consistency and reliability.

High temperature alloys that do not contain or contain aluminum and titanium are generally smelted in electric arc furnaces or non-vacuum induction furnaces. When high-temperature alloys containing high aluminum and titanium are smelted in the atmosphere, element burning is not easy to control, and more gas and inclusions enter, so vacuum smelting should be used. In order to further reduce the content of inclusions and improve the distribution of inclusions and the crystal structure of the ingot, a dual process combining smelting and secondary remelting can be used. The main means of smelting are electric arc furnace, vacuum induction furnace and non-vacuum induction furnace; the main means of remelting are vacuum consumable furnace and electroslag furnace.

Solid solution strengthened alloys and alloy ingots containing low aluminum and titanium (the total amount of aluminum and titanium is less than 4.5%) can be forged to billet; alloys containing aluminum and high titanium generally need to be extruded or rolled. Then hot-rolled into lumber, some products need to be further cold-rolled or cold-drawn. Alloy ingots or cakes with larger diameters need to be forged with hydraulic press or quick forging hydraulic press.

2. Crystallization metallurgy process

In order to reduce or eliminate the grain boundary perpendicular to the stress axis in the cast alloy and reduce or eliminate the porosity, directional crystallization technology has been developed in recent years. This process is to grow crystal grains along a crystalline direction during the solidification of the alloy to obtain parallel columnar crystals without lateral grain boundaries. The first process condition to achieve directional crystallization is to establish and maintain a sufficiently large axial temperature gradient and good axial heat dissipation conditions between the liquidus and solidus. In addition, in order to eliminate all grain boundaries, it is necessary to study the manufacturing process of single crystal blades.

3. Powder metallurgy process

Powder metallurgy technology is mainly used to produce precipitation-strengthened and oxide dispersion-strengthened superalloys. This process can make the generally indeformable cast high-temperature alloy obtain plasticity or even superplasticity.

4. Strength improvement process

⑴Solid solution strengthening

The addition of elements (chromium, tungsten, molybdenum, etc.) with different atomic sizes from the base metal causes the distortion of the base metal lattice, the addition of elements that can reduce the stacking fault energy of the alloy matrix (such as cobalt) and the addition of elements that can slow down the diffusion rate of the matrix elements Elements (tungsten, molybdenum, etc.) to strengthen the matrix.

⑵ Precipitation strengthening

Through aging treatment, the second phase (γ', γ', carbide, etc.) is precipitated from the supersaturated solid solution to strengthen the alloy. The γ'phase is the same as the matrix and has a face-centered cubic structure. The lattice constant is similar to that of the matrix and co-lattice with the crystal. Therefore, the γ phase can be uniformly precipitated in the matrix in the form of fine particles, which hinders the movement of dislocations and produces significant Reinforcement. The γ'phase is an A3B type intermetallic compound. A represents nickel and cobalt, and B represents aluminum, titanium, niobium, tantalum, vanadium, and tungsten, while chromium, molybdenum and iron can be either A or B. The typical γ'phase in nickel-based alloys is Ni3 (Al, Ti). The strengthening effect of γ’ phase can be strengthened through the following ways:

Increase the number of γ'phases;

Make the γ'phase and the matrix have an appropriate degree of mismatch to obtain the strengthening effect of coherent distortion;

Adding niobium, tantalum and other elements to increase the antiphase domain boundary energy of γ'phase to improve its resistance to dislocation cutting;

Adding cobalt, tungsten, molybdenum and other elements to increase the strength of the γ'phase. The γ'phase has a body-centered tetragonal structure, and its composition is Ni3Nb. Due to the large degree of mismatch between the γ'phase and the matrix, it can cause a large degree of coherent distortion, which makes the alloy obtain a high yield strength. But above 700°C, the strengthening effect is significantly reduced. Cobalt-based superalloys generally do not contain γ phase, but are strengthened with carbides.