High-temperature thermocouples, especially type C variants, are essential components in extreme manufacturing environments where temperatures can exceed 2000°C. One such application is in Hot Isostatic Pressing (HIP), where densification of materials like metal and ceramics occurs under extreme pressure and heat in an inert atmosphere. This allows for the production of materials and components with high relative density, which greatly enhances their reliability and strength.
Kamet’s specialized duplex type C thermocouples – featuring tungsten-coated molybdenum sheaths and hafnia (HfO₂) insulation – are engineered to deliver high accuracy, long service life, and mechanical robustness in these extreme furnace environments. The thermocouples have a pivotal role in ensuring furnace precision and efficiency.
What is the working principle of HIP furnaces?
HIP systems perform a pressure-assisted sintering process. Components are placed in a sealed graphite furnace where argon or nitrogen gas is pressurized up to 2000 bar and heated to 2000°C or higher. The high temperature combined with the uniformly applied gas pressure (isostatic) causes residual gases in the treated material to bubble to the surface and be eliminated. This enhances the densification and reduces the porosity of ceramic and metallic materials and components.
Our duplex type C thermocouples (W5%Re/W26%Re) are inserted into the graphite furnace structure to perform system critical temperature control. The following illustration shows the general design of a HIP system with thermocouple placement:
Below is a table of the temperatures and pressures required for common materials used in hot isostatic pressing.
| Material | Temperature/°C | Pressure/MPa |
|---|---|---|
| Aluminum alloy | 500 | 100 |
| Copper alloy | 800–950 | 100 |
| Stainless steel | 1150 | 100 |
| Nickel 718 | 1185 | 100 |
| Ti-6Al-4V | 950 | 100 |
| WC-Co | 1700 | 100 |
| Tungsten | 1350 | 100 |
| Beryllium | 900 | 100 |
| Molybdenum | 1350 | 100 |
| Pure Iron | 950–1160 | 100 |
| Pure Nickel | 1100–1280 | 100–140 |
What is the importance of HIP furnaces?
HIP furnaces offer a range of benefits for the advanced manufacturing of materials. These include the consolidation of powder metal and ceramic parts, the healing of defect castings and diffusion bonding of materials. It’s unique in its ability to treat large and complex geometries. HIP treatment reduces the need for costly welding of critical joints.
What role does the thermocouple play in HIP furnaces?
The thermocouples provide precise and stable temperature measurement throughout the pressurization and cooling cycles. This is critical to ensure product consistency. Furthermore, overheating or underheating can cause energy waste and material defects, the thermocouple helps avoid this through precision control.
In what way are Kamet’s duplex type C thermocouples specialized for HIP furnace use?
The thermocouple construction includes:
- Tungsten-coated molybdenum sheaths: These resist carburization from the HIP graphite furnaces at high temperatures, maintaining sheath integrity.
- Hafnium dioxide (HfO₂) insulation: Offers exceptional stability and electrical insulation at extreme temperatures.
- Epoxy or high-temperature ceramic cement transitions: Depending on design requirements (standard vs. high temperature thermocouples).
Furthermore, the following properties of our duplex type C duplex thermocouples make them specifically suited to HIP furnace applications:
- Extreme temperature resistance – Suitable for continuous operation up to 2300°C.
- Pressure-ready design – Robust design suitable for hydrostatic environments up to 2000 bar.
- Graphite furnace compatible – Tungsten coating prevents molybdenum carbide (Mo₂C) formation caused by interaction with the graphite HIP furnace.
- Accurate dual sensing – Duplex design allows for redundancy or cross-checking critical readings.
- Vacuum and inert gas operation – Sealed design prevents contamination and loss of accuracy in both argon (Ar) and nitrogen (N₂) atmospheres.
- Tailored insert lengths – the standard lengths of 13” and 24”, can be customized based on customer specifications and tube availability.
- Proven performance – Kamet has supplied thermocouples to HIPERBARIC, one of the world’s leading HIP system manufacturers.
Which industries make use of HIP processes?
One of the advantages of HIP furnaces over other high pressure sintering is that they can treat complex components like metal castings or 3D-printed parts. Some examples of industries using these processes include:
- Aerospace & defense manufacturing – Thermal profiling during densification of turbine blades, rocket parts, and structural alloys. Densification is an essential safety aspect to avoid the failure of parts.
- Additive manufacturing (AM) post-processing – Ensuring dimensional accuracy and mechanical strength of printed parts.
- Medical and industrial components – HIP cycles are used for manufacturing implants, surgical tools, and wear-resistant coatings.
- Energy sector – power generation components, such as turbine parts, heat exchangers and the large parts required for nuclear reactor pressure vessels. HIP provides components with increased wear and corrosion resistance, a vital aspect to meet the stringent demands.
- Powder metallurgy – the elimination of residual porosity in powder metallurgy sintered parts
- Ceramic processing – HIP is used to make ceramics suitable for high-performance applications by increasing their density and improving their mechanical properties
- Castings – the casting process often produces micro pores during cooling and solidification. This can cause low-stress cracking and fatigue damage. Treatment through HIP can resolve these issues.
- Processing radioactive waste – absorbed gases are removed from the waste and the remaining material is shrunk. This minimizes the space required for transport and disposal.
Kamet’s thermocouples: quality and service
Kamet’s duplex type C thermocouples represent the cutting edge of temperature measurement in HIP environments. Developed through close collaboration with HIPERBARIC and leading sensor manufacturers, our solutions are designed to withstand extreme thermal, chemical, and mechanical stress. With advanced materials like tungsten-coated molybdenum and HfO₂ insulation, and optimized transitions, Kamet delivers reliable thermocouples ready for tomorrow’s high-performance industries. We pride ourselves on exceptional customer service, so contact our specialists about any thermocouple questions you may have.