APPLIED MATERIALS & FIELDS

Aero engines are mainly made of aluminum alloy, titanium alloy, high temperature alloy, steel and other materials, with a variety of parts. Its forming technology is very complex and diverse. With the development of engine towards lightweight, high performance and long life, the parts must adopt high performance materials and integral forming technology to meet the above requirements.

Hot isostatic pressing (HIP) has shown strong technical and economic advantages especially in the manufacturing of titanium alloy and nickel-based superalloy components. Through the HIP treatment, the parts can reach its 100% theory density, and eliminate the inherent internal defects of titanium alloy and superalloy precision casting process, such as pores, internal cracks, local porosity, etc., thus improving the overall mechanical properties of the parts, especially the fatigue performance, while reducing the cost and improving the energy efficiency.

As the power machine with the highest heat-power conversion efficiency so far, gas turbine is widely used in mechanical drives (such as ships and trains) and large power stations. As a kind of rotating impeller engine, gas turbine compressor blade is the core component of heavy gas turbine. Because the impeller has to work stably at 1400℃-1600℃ for a long time, it is a working environment with extremely high requirements for material quality and performance. Therefore, the blades of heavy gas turbine should be made of high temperature alloy materials.

In the process of casting, slag inclusion, crack, porosity, and deformation of the material will affect the strength and performance of the blade. These defects are impossible to avoid in the production process itself, and can only be solved through the subsequent treatment. HIP is one of the important processes.

After HIP treatment, the superalloy can basically eliminate the residual defects and deformation problems in precision casting, greatly improve the material performance and anti-fatigue ability, and thus significantly improve the service life of gas turbine. Compared with single crystal blade, it has a huge cost advantage. At present, the working time of heavy gas turbine blades has been improved to 30,000 to 50,000 hours, which is nearly 50% longer than the service life of traditional components without HIP treatment.

In the process of additive manufacturing, defects such as pores and microcracks, residual stresses will remain inside, and the size and type of defects will be determined by the specific printing process parameters. These defects have great influence on the mechanical properties of materials, especially the fatigue properties. By HIP post treatment, these defects can be eliminated and the density of the material will reach the theoretical value.

Fatigue strength is an important factor in some important components, such as aerospace components and medical implants. For these components, HIP processing is a routine procedure. Compared with the original material, the yield strength of HIP-treated products decreases, but the ductility increases. Due to the cooling rate of several thousand degrees per second during additive manufacturing, the material produces high yield strength. During subsequent conventional heat treatments, such as HIP and annealing, the microstructure becomes coarser, resulting in a decrease in yield strength but an increase in ductility.

• HIP treatment can process 3D printed products quickly and in large quantities.

Whether micro pores or large amounts of pores generated in the 3D printing process, they all can be completely eliminated by HIP processing. Therefore, there is no need to put forward high requirements for the 3D printed products processed at one time. A large number of "low quality products" can be produced first, and then the products can meet the requirements through batch processing of HIP treatment, greatly saving time and cost.

In addition, because the pores in the material in the additive manufacturing are evenly distributed inside, the volume contraction in all directions is uniform in the process of HIP densification, and there will be no deformation as in the general powder metallurgy NNS process. At the same time, the residual stress of the product will be released.