Perfect materials, Perfect products

   Hot Isostatic Pressing (HIP) is a special heat treatment process for metal or ceramic materials, which is a means to produce high-performance materials. The technology can be used for powder metallurgy molding , densification of the molded castings or 3D-printed products, or diffusion bonding of two or more different materials. After HIP treatment, the wear resistance, corrosion resistance and mechanical properties of the material will be greatly improved, and the fatigue life can be increased by 10~100 times.

Processing characteristics:

• High Temperature - reach up to 2000℃

• High Pressure – reach up to 200 MPa

• Isostatic Pressure - Using inert gas as the pressure transfer medium, and the same pressure is applied evenly to the surface of the parts from all directions

Main application material system:

Superalloy, titanium alloy, aluminum alloy, copper alloy, refractory metal, hard alloy, stainless steel, corrosion resistant alloy, ceramics, composite materials, electronic materials, functional materials, etc.

   As we all know, any materials have a certain fatigue life, could not be indefinitely used. There are two fundamental reasons for material failure. One is composition changes in the internal structure of the material. The new composition cannot achieve the appropriate performance, and the material immediately fails. Another more common reason is the internal residual impurities, tiny cracks, voids, residual stresses etc. in materials, to form the performance break point, which we call “material defects”. When materials work, such as the high temperature circulation loop, the stress concentration effects at the location of the performance break point, eventually make the material fracture failures. So far, none of the traditional molding methods can directly eliminate the residual defects in the material, and the subsequent processing is always needed.

   Of course, in a normal working environment, there is no need to put forward excessive requirements on the performance of the material. Some defects are allowed as long as they do not affect the use of the material. But in some special working environment, such as aircraft engines, nuclear reactors, gas turbine, offshore oil exploitation, and so forth, the material need to bear high temperature, pressure, amplitude or corrosive environment. On this occasion, very high material performance are required, in addition to high strength, toughness, corrosion resistance, high stability is necessary. At this point, it becomes particularly important to eliminate the internal defects of the material.

     As a special metal heat treatment process, HIP now is the most effective heat treatment method to eliminate the internal defects of materials, and it is also the material forming method to minimize the internal defects of materials. Therefore, it becomes a routine processing procedure for key parts in various fields worldwide.

According to the needs of products to be processed, HIP treatment services can be divided into the following THREE categories:

   During the service process of the material, the residual pores and tiny cracks in the material are not only the fracture initiation points, but also the wear and corrosion initiation points. In aircraft engine, nuclear reactor, gas turbine and other complex working environment, the material fracture failure will cause very serious consequences. After the HIP treatment, the internal structure of the material densifies, all pores and defects disappear, forming a uniform and dense texture, which greatly improves the wear-resistance, corrosion resistance, mechanical properties and fatigue strength of the material.

   In the casting process, due to the uneven temperature diffusion of the material during cooling, internal porosity, segregation, shrinkage cavity, microcrack and other inherent defects of the process will be produced, which will reduce the material mechanical properties, service life and stability. Similarly, in metal injection molding and 3D printing processes, there are also problems such as loose internal structure of materials, residual defects and internal stresses.

   HIP densification processing refers to putting the castings, MIMs, 3D-printed products, or other products with defects inside, in the HIP fuanace, by inert gas as the transmission medium, exert the high temperature, high pressure and isostatic pressure on their surface. Such exertion force products deformed under the solid phase, on the atomic diffusion level, pore and tiny crack thus disappear. Due to the elimination of the material internal fracture initiation point (stress concentration point), the overall performance of products are greatly improved.

      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.