Exploring Refractory Metals: Characteristics and Industrial Significance

Key Properties of Refractory Metals

Refractory metals are defined by their high melting points, exceptional strength, and resistance to deformation under extreme conditions. However, their mechanical properties vary, which influences their suitability for different industrial applications. While these metals are inherently strong, their surfaces often need enhancement to improve wear resistance, reduce oxidation, and prevent mechanical failure under extreme conditions.

Characteristics and Challenges

Tung­sten (W)

Tungsten was discovered in 1781 by the Swedish chemist Karl Wilhelm Scheele. Therefore, the name is derived from the Swedish words “tung” (heavy) and “sten” (stone).

The melting point of tungsten is at, 3410° C, which is the highest of all metals. Further, it is one of the most dense metals in the world (19.3 g/cm3) and shows the highest conductivity in comparison to other refractory metals. In addition, tungsten becomes one of the hardest man-made materials, when combined with carbon.

The metal is best known for its use in manufacture of filaments for light bulbs. Moreover, it is commonly used in industrial lightning as electrodes in arc lamps. Further use finds the element in metal cutting, mining and oil drilling tools.

Molyb­de­num (Mo)

Molybdenum was firstly used in 1894 by a French company as an armor plate and is the most popular of all refractory metals. The primary application of molybdenum is as an alloying element in steel, as it is widely used in the manufacture of pipelines, tools and stainless steel. Especially the alloy TZM, which stands for Titanium (0.5 %), Zirconium (0.08 %) and Molybdenum, is quite popular, due to its great creep resistance and strength at high temperatures. Further applications are molybdenum are high-heat applications such as furnace parts or elevator brakes.

Molybdenum shows superior electrical conductivity (2×107 S/m). In fact, it is the highest of all refractory metals. The heat conducting capabilities (138 W/(m*K)) are superior as well. Other properties are good corrosion and wear resistance and high tensile strength.

Nio­bi­um (Nb)

Niobium is also known as Columbium (Cb) and was firstly discovered in 1801 in Connecticut. Usually, Niobium is found together with Tantalum and both elements share similar properties. The main difference is however the weight, as niobium is only half as heavy as tantalum.

Niobium is the least dense of all refractory metals. Moreover, it is the only one, which can be worked through annealing. Therefore, it shows great machinability at low temperatures and can achieve a wide range of strength and ductility.

The main application of niobium is as an alloying element of steel. Due to the low density, the element fits perfectly for the manufacture of high-performance refractory workpieces with low weight. Therefore, it is often applied in the aerospace industry, but also in gas turbines and nuclear reactors.

Tan­ta­lum (Ta)

As already mentioned, tantalum was discovered at the same time as Niobium and shares a lot of its characteristics. An outstanding property of tantalum is the superb corrosion resistance, especially in nitric, hydrochloric and sulfuric acid and acidic environments overall. Overall, it has good mechanical properties.

The main fields of application for tantalum are in the medical industry. There, it used for surgical equipment. Due to its superior corrosion resistance, tantalum is applied as chemical equipment such as vapor condensers, orifices and reaction vessels. Further, it is used in the manufacture of electrolytic capacitors, as it shows the second-best capacitance of all substances.

Rhe­ni­um (Re)

Rhenium does not have a specific ore, as it was discovered by German scientists in platinum and columbium ores in 1925. Thus, it is the most recently discovered refractory metal of all. Since the element occurs so rarely, it is the most expensive of all refractory elements.

Most often, rhenium is used as an alloy for other refractory metals. In this way, the ductility and tensile strength can be enhanced greatly. It is typically applied in the construction of nuclear reactors, gyroscopes and electronic components. However, the most common use of rhenium is as a catalyst for reaction such as oxidation or hydrogenation.

Surface Hardening: Enhancing Refractory Metals

Although refractory metals offer excellent mechanical properties, they still face challenges such as wear, oxidation, and galling. Surface treatments are necessary to enhance their durability and ensure long-term performance in extreme conditions.

Common failure mechanisms include:

• Abrasive wear: Metal-to-metal contact and exposure to abrasive particles cause gradual material loss.
• Oxidation: High temperatures accelerate the breakdown of refractory metals, reducing their lifespan.
• Galling and fretting: Under high loads, surfaces can adhere and tear, leading to severe damage.

Diffusion-based hardening processes such as BORINOX®, BOROCOAT®, and NICKELCOAT® are more effective than traditional coatings like PVD or CVD, which can suffer from poor adhesion and thermal stress.

Industrial Applications

Refractory metals are used in a wide range of industries where conventional materials would degrade under heat and mechanical stress.

• Aerospace and defense: Jet engines, rocket nozzles, and missile components require materials that can withstand extreme temperatures and mechanical loads.
• Energy sector: Nuclear reactors, fusion technology, and high-temperature turbines depend on refractory metals for their radiation resistance and thermal stability.
• Industrial manufacturing: High-performance tools, furnace components, and extrusion dies use these metals for their durability in harsh environments.
• Medical technology: Tantalum is widely used in implants due to its biocompatibility and resistance to bodily fluids.
• Electronics and semiconductors: Molybdenum and tungsten play a crucial role in microelectronics, heat sinks, and vacuum tube components.

BorTec’s Advanced Surface Hardening Solutions

BorTec offers specialized diffusion treatments that enhance the wear resistance and longevity of refractory metals.

• BORINOX® (Diffusion Hardening): This process introduces nitrogen and carbon into the surface of refractory metal alloys, significantly increasing hardness while maintaining resistance to corrosion. It is particularly effective for nickel-based alloys, which are often used in aerospace and industrial applications.
• BOROCOAT® (Boronizing): By diffusing boron into the metal surface, BOROCOAT® creates a super-hard boride layer with a hardness of up to 2600 HV. This treatment enhances wear resistance and prevents galling, making it ideal for high-performance industrial applications.
• NICKELCOAT® (Electroless Nickel Plating): This process deposits a uniform high-phosphorus nickel layer onto refractory metals, providing exceptional corrosion protection. It is widely used in harsh environments, such as the oil and gas industry, where materials are exposed to acidic and corrosive conditions.

Each of these treatments improves the surface properties of refractory metals, ensuring better performance and extended component lifespan.

Protecting Your Components with BorTec’s Solutions

Refractory metals are essential in industries that demand high-performance materials capable of withstanding extreme conditions. However, to maximize their potential, these metals often require advanced surface hardening techniques. Technologies such as BORINOX®, BOROCOAT®, and NICKELCOAT® provide superior wear and corrosion resistance, reducing maintenance costs and extending component lifespans.

For manufacturers and engineers working with refractory metals, investing in specialized surface treatments is a crucial step toward ensuring durability and efficiency. Contact BorTec today to learn how our innovative hardening solutions can enhance the performance of your refractory metal components.