Past and Present of Hot Isostatic Pressing Technology

Hot isostatic pressing is a process technology that uses high temperature and high pressure to make metal or ceramic products withstand isotropic and equal pressure, so that the parts can be sintered and densified. It has the advantages of stable chemical composition, isotropic mechanical properties, good structural adaptability and low cost.

01. Past life of hot isostatic pressing - high temperature pressure bonding

The research on hot isostatic pressing technology (HIP) began in 1955. It was carried out by the Battelle Institute of the United States for the development of nuclear reactor materials. It was first used for the diffusion bonding of fuel elements in the atomic energy reaction process. Based on this application, the researchers at that time Give it a very common but intuitive name - high temperature pressure bonding.

In 1963, the technology was introduced to Europe. The Swedish ASEA company used the prestressed steel wire winding structure to manufacture high-pressure vessels. Its structure is compact, safe and reliable, and it has laid a solid foundation for the vigorous development of HIP technology.

Ten years after the birth of hot isostatic pressing technology, the advent of the first hot isostatic pressing machine marked the birth of hot isostatic pressing technology equipment.

In the 1960s, researchers used the hot isostatic pressing process to successfully coat materials such as zirconium alloy and stainless steel on uranium dioxide, achieving bonding and densification at the same time, and obtaining good results. First application of hydrostatic technology in industry. In the mid-1960s, the successful development of powder produced by gas atomization method played a role in promoting the development of hot isostatic pressing technology.

02. The current life of hot isostatic pressing - efficient near-net shape/densification technology

In the following decades, countries competed to develop and apply isostatic pressing equipment. After Sweden developed a hot isostatic pressing machine with compact structure, light weight, small size, easy installation, safety and reliability in 1965, this situation was especially active.

Today, hot isostatic pressing equipment is becoming more and more intelligent, automated, and large-scale, and hot isostatic pressing technology is becoming more and more advanced, becoming a simple and efficient near-net shape densification technology.

03. Hot isostatic pressing equipment and densification principle

Hot isostatic pressing equipment consists of high-pressure vessels, heating furnaces, compressors, vacuum pumps, gas storage tanks, cooling systems and computer control systems, among which high-pressure vessels are the key devices of the entire equipment. The following figure shows a typical hot isostatic pressing system schematic diagram.

Schematic diagram of hot isostatic pressing system

The hot isostatic pressing densification process is to place the product in a closed container, input high-pressure argon gas into the container through the compressor, and heat it through the heating furnace in the container at the same time, so that the product can be processed under the action of high temperature and high pressure at the same time. densification.

Schematic diagram of hot isostatic pressing technology

The hot isostatic pressing densification process can be divided into two stages. The first stage is that the internal defects and pores undergo plastic deformation under the condition that the external pressure is greater than the high temperature strength of the material, and the defects and pores are destroyed, causing the inner surfaces to contact each other; In the second stage, when the external pressure is lower than the high-temperature strength of the material, the material undergoes high-temperature creep, and at the same time, the contacted alloy surfaces penetrate each other, diffuse and bond, and completely eliminate defects and pores. Through this treatment, the material density is basically close to the theoretical density.

04. Application of hot isostatic pressing technology

Hot isostatic pressing technology is currently not only used in casting processing, powder metallurgy, and ceramic industry, but also in the fields of porous materials, near-net shape, material bonding, plasma spraying, and manufacturing of high-end graphite.

Application fields of hot isostatic pressing technology and materials involved

Hot isostatic pressing technology is currently not only used in casting processing, powder metallurgy, and ceramic industry, but also in the fields of porous materials, near-net shape, material bonding, plasma spraying, and manufacturing of high-end graphite.

1. Casting densification treatment

Generally speaking, there are problems of shrinkage, porosity and porosity inside castings, and these defects reduce the performance and reliability of materials, especially in alloy materials, these tendencies are particularly prominent. These defects can basically be eliminated by using hot isostatic pressing technology. To eliminate such defects, the jacket has to be used as a pressure transmission medium. The significance of hot isostatic pressing of castings is mainly reflected in the following aspects:

(1) After hot isostatic pressing, it can reduce the scrap rate of castings during X-ray inspection and surface transmission inspection;

(2) Compared with untreated castings, HIP-treated castings have fewer cracks after welding, thus reducing the cost of repair welding;

(3) Hot isostatic pressing treatment can improve the range of casting parameters and expand the variety of new casting alloys;

(4) Hot isostatic castings with improved fatigue strength and ductility can replace expensive forgings.

2. Application in powder metallurgy

In order to obtain a uniform and refined structure, reduce material loss, and reduce subsequent machining, more and more powder metallurgy products are formed and densified by hot isostatic pressing. Such as powder metallurgy high-speed steel; stainless steel, such as AISI-304 stainless steel; powder metallurgy superalloys, such as aircraft engine turbine discs; various radiation targets; powder metallurgy parts for automobiles; chemical pumps, valves and multi-channel distribution pipes, etc. The performance of the product after powder metallurgy (PM) plus HIP treatment has the following advantages compared with the products of conventional smelting and thermal processing:

(1) The material has good uniformity, no segregation, good mechanical properties and corrosion resistance, and isotropy. At the same time, the stability of each batch of materials is also good.

(2) The grains of the material produced by the PM-HIP process are finer than those processed by the conventional process, so it is convenient to use ultrasonic non-destructive testing for inspection.

(3) Since it can be made into final size products, less material is used. According to statistics, the price of products made by PM-HIP technology is more than 20% lower than that of products made by conventional technology.

(4) Since the mold used in the current PM-HIP process can already be welded with steel plates, its shape can be changed arbitrarily, and the design freedom of parts is relatively large.

3. Application in ceramic materials

Hot isostatic pressing technology is used in the production of ceramic materials, which improves the molding and sintering conditions, significantly reduces the porosity of the material, thereby improving the performance of the material, and provides an effective method for manufacturing ceramic materials. These methods mainly include: porous High-temperature impregnation, diffusion bonding, sintering + hot isostatic pressing, hot isostatic pressing powder consolidation and hot isostatic pressing forging of ceramics.

4. HIP cladding and HIP composite diffusion connection

HIP cladding and HIP composite diffusion bonding are another important application of HIP. Hot isostatic pressing coating technology is a new technology that uses hot isostatic pressing technology to prepare a coating with special physical or chemical properties on a material to improve its comprehensive performance; hot isostatic pressing composite diffusion connection is to combine Two or more different materials, a new technology of diffusion connection under high temperature and high pressure, the materials involved can be metal-metal, metal-nonmetal, nonmetal-nonmetal, it is a new technology in recent years Developed, especially a better technology worthy of application and promotion in civilian use.

The characteristics of hot isostatic pressing cladding and hot isostatic pressing composite diffusion connection are:

(1) For the same or different materials, a strong connection interface can be produced;

(2) The interface cannot be seen, and the dispersion is uniform;

(3) The mechanical properties of the interface reach the properties of the base metal, resulting in a uniform microstructure;

(4) There is no need to melt the base metal, and the connection temperature is generally 50% to 70% of the melting point, and at the same time, no other defects caused by the melting of the base metal will occur;

(5) It can handle parts with complex geometry.

5. Other new fields

In addition to the above-mentioned main application areas, HIP technology also includes the following applications:

(1) In the application of porous materials, since nitrogen is used as the medium, nitrides are formed at high temperatures, so that HIP also has an effect on porous materials;

(2) Combine HIP technology with surface treatment such as nitriding to expand HIP function;

(3) HIP technology can be used to prepare high-purity materials by suspension smelting process, because the density of high-pressure gas increases, which can suspend the smelting material and realize crucible-free smelting, thereby greatly improving the smelting purity;

(4) The food industry adopts HIP technology, and applying high pressure to food can achieve the purpose of sterilization and disinfection without destroying the nutrition and maintaining the original color and taste of the food, providing a new way for food processing;

(5) Material bonding. Material bonding is the most original application of hot isostatic pressing technology, which has been recognized by the American Welding Society. Under the hot isostatic pressing process conditions, more than two kinds of the same material or different materials can be firmly bonded together to form a whole. The advantage of this bonding process is that the processing cost is low, the bonding temperature is low, and the performance of the bonding area is similar to that of the substrate;

(6) Manufacture of high-end graphite products, which combines molding and roasting into one, simplifies the process steps, saves production costs, and reduces the number of times of roasting and impregnation.

Summarize

The use of hot isostatic pressing densification technology can not only greatly improve the comprehensive performance of castings, but also shows irreplaceable advantages in the densification of brittle materials such as ceramics and hard alloys that cannot be densified by traditional processes. In short, after nearly 70 years of development, hot isostatic pressing has been fully developed, and it is widely used in the production and life of the people. Especially in today's high demand for new materials and new energy, HIP technology has given full play to its unique advantages and brought a qualitative leap in the technological level of all walks of life.