Tungsten - Refractory metalUndoubtedly one of the most revolutionary products of technology to emerge in recent years has been the 3D printer. Though not a new concept per se, parallel advances in material science have seen it become an important tool in a number of diverse industries that have adopted a method of production known as additive manufacturing. Rather than starting with a chunk of raw material and machining it to remove unwanted material to fashion an item, the finished item is created from a succession of layers that are fused together with no waste. Among the materials that might potentially be used in this way are sintered refractory metals.

Much of the manufacturing performed in this fashion relied, until relatively recently, on the use of plastics, ceramics, and fine metallic particles. When using such materials, varying degrees of heat, adhesives, pressure, or some appropriate combination of these will provide an effective means to bind the successive layers of an item. Remarkable though it may seem, giant-sized 3D printers have even shaped concrete to create the entire infrastructure of a home as a single, cohesive unit. In some cases, however, a product may need exceptional qualities, such as resistance to high temperatures or corrosion. For this type of application, the use of sintered refractory metals in 3D printers may soon provide the solution.

Molybdenum, tungsten, tantalum, rhenium, niobium, and chromium are the six most commonly used of around twice that number of metallic elements characterised by their exceptionally high melting points. Other desirable properties of the group are their hardness, high density, resistance to corrosion, and good electrical conductivity. Their high melting points make them ideal for the manufacture of components for the aerospace and automotive industries, for example. However, it also means that components manufactured from these cannot easily be produced by casting. For this purpose, powdered refractory metals must, instead, be sintered.

An alternative means by which to fashion materials into some desired form, sintering makes use of heat and pressure to compact and bind particles together without the need to actually liquefy them. The use of this type of procedure is particularly valuable in the case of elements such as tungsten. Its melting point, at 3 420 °C, is the highest of all the metallic elements of which it is also the hardest by far, and so creating cast items from this near-indestructible element would be totally impractical. Tungsten, like other refractory metals, needs to be sintered.

A process known as direct metal laser sintering or DMLS is already being used successfully for the additive manufacture of small metal components for tools, aerospace parts and even for medical implants. However, until 3D printing technology can handle materials such as tungsten and molybdenum as effectively as it can manipulate other materials, more traditional methods must be used.

The applications for these exceptional elements are numerous. Tungsten, for instance, is used to manufacture the crucibles use in processing uranium and to manufacture NASA’s rocket nozzles, while molybdenum is used to make stainless steel, superconductors, and heat shields for high-temperature vacuum furnaces.

LIT Africa is a foremost supplier of high-grade, powdered refractory metals.