Tungsten-Rhenium Spooled Wire (W95-Re5)

Tungsten-rhenium alloy (W95/Re5) wire is the + leg of the Type C thermocouple, which operates at up to 2,000 °C (vacuum/inert/protective atmosphere only). Tungsten-rhenium alloys are specified for thermocouple applications above the useful range of all platinum-based types (approximately 1,600 °C), covering vacuum furnaces, sintering systems, and metallurgical processes that require temperature measurement up to and beyond 2,000 °C. The rhenium addition to tungsten significantly improves ductility and wire-drawing characteriztics compared with pure tungsten, which is too brittle to draw reliably to fine thermocouple gauges.

Tungsten-rhenium alloys oxidize rapidly above approximately 500 °C in open air. W95/Re5 wire — and all tungsten-rhenium thermocouple wire — must be used in vacuum, inert (argon, helium), or protective atmosphere environments only. Exposure to oxygen at elevated temperatures causes irreversible oxidation that destroys the thermocouple within minutes. This atmosphere restriction is the defining operational constraint of Type C thermocouples and must be observed throughout the service life of the thermocouple element, including during installation and any maintenance operations.

Type C is specified wherever temperature measurement above the platinum-rhodium limit (approximately 1,600 °C) is required under protective atmosphere. Primary applications include vacuum furnaces for sintering, annealing, and brazing of refractory metals and ceramics; arc melting and casting of refractory alloys; nuclear reactor fuel and cladding development; plasma physics research; aerospace propulsion testing; and high-temperature materials characterization. These are all environments where the vacuum or protective atmosphere requirement is already present for process reasons, making the atmosphere constraint of tungsten-rhenium thermocouples a natural fit rather than an additional burden.

Both Type C and Type D are tungsten-rhenium thermocouple types for extreme high-temperature vacuum or protective-atmosphere service. Type C uses W95/Re5 (positive) and W74/Re26 (negative), covering up to 2,000 °C. Type D uses W97/Re3 (positive) and W75/Re25 (negative), covering up to 2,315 °C — the highest temperature ceiling of any standard thermocouple type. Type D also offers slightly improved ductility in the negative leg (W75/Re25 vs W74/Re26) due to the different rhenium distribution. For most vacuum furnace applications below 2,000 °C, Type C is the established standard; Type D is specified where the additional temperature headroom of 315 °C is required.

Pure tungsten is extremely brittle in wire form, making it difficult to draw to fine gauges and prone to fracture during handling and installation. The addition of rhenium — through the 'rhenium ductilising effect' — significantly improves the room-temperature ductility of tungsten, allowing it to be drawn to thermocouple-grade diameters and handled without fracture. The specific rhenium percentages used in Type C and D thermocouples (W95/Re5 and W74/Re26 (Type C negative leg)) are optimized to balance ductility, thermoelectric sensitivity, and reproducibility of the EMF-temperature relationship.

Tungsten-rhenium wire is significantly more brittle than nickel-based or platinum-based thermocouple wire and must be handled carefully to avoid kinking, bending to tight radii, or mechanical shock that would cause fracture. The wire should be wound onto sufficiently large diameter formers and should not be bent to radii below the minimum specified for the gauge. During installation in furnace systems, the thermocouple should be supported along its length to prevent vibration-induced fatigue at high temperatures. The atmosphere must be established before the wire is heated above 500 °C.

Tungsten-rhenium thermocouple wire is used in nuclear reactor instrumentation where measurement of fuel, cladding, and coolant temperatures in high-flux environments under protective atmosphere is required. Its radiation hardness and high-temperature capability make it suitable for in-pile measurements in fission reactor development and fusion reactor diagnostics. In materials science, it is used for temperature measurement during high-temperature testing of refractory metals, ultra-high-temperature ceramics, and nuclear fuel materials where the protective atmosphere required for the specimen is also suitable for the thermocouple.

Tungsten-rhenium alloy (W95/Re5) spooled wire is available in a range of diameters and lengths suited to thermocouple fabrication. Diameter tolerance is ±10% and length tolerance is +5% / −1%. For custom configurations, please contact us.