Method used for forming of thick plate blanks from high-temperature direct forging of TiAl alloy powder

Abstract

The invention relates to a method used for forming of thick plate blanks from high-temperature direct forging of TiAl alloy powder, and belongs to the technical field of hot working of TiAl alloy. Themethod used for forming of the thick plate blanks from high-temperature direct forging of the TiAl alloy powder comprises the following steps: firstly, filling to-be-machined jackets with the alloy powder, sequentially conducting treatment of vacuumizing, heating and heat preservation, and vacuumizing to obtain powder ingot blanks, and conducting soldering and sealing on air vents; then placing the powder ingot blanks into a high-temperature furnace, conducting heating to elevate the temperature to 1400-1440 DEG C, and then conducting heat preservation; then conducting forging by adopting a forging machine in radial directions of the powder ingot blanks, and maintaining pressure for 20-30 s after forging is conducted, wherein under the binding action of an upper die and a lower die of theforging machine and the jackets, the alloy powder in the powder ingot blanks start to collide with each other, and is subjected to forming after being subjected to plastic deformation; and finally, placing the powder ingot blanks, subjected to forging and pressure maintaining, in air, conducting natural cooling until the temperature drops to a room temperature, and removing the jackets. Comparedwith a hot isostatic pressure technology, the method used for forming of the thick plate blanks from high-temperature direct forging of the TiAl alloy powder has the advantages that due to short heating time, few PPB particles participate, and the plastic deformation amount is large, so that original PPB networks are thoroughly destroyed, and adverse effects of PPB on the mechanical performance ofthe material (TiAl alloy powder) can be reduced.

Description

technical field [0001] The invention belongs to the technical field of TiAl alloy thermal processing, and in particular relates to a method for directly forging TiAl alloy powder at high temperature to form a thick plate blank. Background technique [0002] TiAl alloy is a light-weight high-temperature structural material with great application potential. It is mainly used in engine blades and exhaust valves in the aerospace field. TiAl alloy not only has good creep resistance, but also structural parts made of TiAl alloy still have a strong elastic modulus at high temperatures, and can maintain strength and other properties at 750°C, so they can be used during service. Withstand high frequency vibration. Furthermore, the density of TiAl alloy is low, which is 4g / cm 3 , which is only half the density of high-temperature nickel-based alloys, and is expected to replace nickel-based superalloys in turbine engines to achieve a weight reduction of 20% to 30%. [0003] However,...

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Problems solved by technology

Although the casting metallurgy method has the advantages of low cost and simple process, the crystal grains of the structure obtained by the casting metallurgy method are relatively coarse, and there may be shrinkage cavities, shrinkage porosity and internal defects, resulting in low mechanical properties of the alloy.

Although the alloy with good unidirectional performance can be obtained by directional solidification, due to the high chemical activity of the TiAl alloy melt, it is easy to react with the shell material at high temperature, causing contamination on the surface and interior of the alloy, and deteriorating the performance of the alloy.

Powder metallurgy has significant advantages in eliminating casting defects, uniform microstructure and composition, and near-net shape. Among the methods currently used for direct powder forming, hot isostatic pressing has been favored by many researchers, but hot isostatic pressing At present, there are still some deficiencies in the pressing technology. Although the alloy obtained by the hot isostatic pressing process can be rapidly densified, the alloy formed under high temperature and high pressure is in an unstable state, and usually requires a certain period of heat treatment to make the alloy in the unstable state The TiAl alloy can be applied in industry only after it has fully reacted and transformed into a stable TiAl phase.

[0005] In addition, a problem worthy of attention is: due to the existence of certain element segregation on the surface of the powder during the cooling process of powder making, some oxide spots will also be generated on the surface.

Although the PPB grid has high strength at high temperature, its plasticity is poor, which may form a potential source of cracks, resulting in a decrease in the mechanical properties of the alloy

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