Editorial Feature

Tungsten Applications - Special Applications

Cobalt-chromium-tungsten alloys, frequently called stellite, are a group of wear resistant alloys which are used for bearings, valve seats and pistons, mill inliners, etc., i.e. applications where a tough wear resistant material is required.

Superalloys are nickel, cobalt or iron based alloys with high contents of tungsten, molybdenum, tantalum and, more recently, also rhenium, for applications where extreme mechanical strength combined with excellent erosion resistance at high temperatures is needed, e.g. in turbine blades for aircraft, space vehicles etc.

Tungsten heavy metal (heavimet, densalloy) is a sintered pseudoalloy of tungsten with an iron-copper or iron-nickel binder for applications where a non-brittle high density material is required, e.g. for counterweights in aeroplanes, for darts, or for weights in golf club heads. It is also used in armament applications, for example as high velocity penetrators in anti-tank weapons. The density of available grades ranges from 17 up to 19 g/cu cm.

Tungsten is frequently used as an additive to tantalum (max. 10 % W) and niobium (max. 15 % W) to improve high-temperature strength and creep resistance.

Wear Protection

Several techniques are in use to protect equipment against wear.

Functional or structural parts can be made completely from cemented carbide, stellite or a superalloy. Alternatively, cemented carbide parts can be soldered onto selected surface areas.

Hardfacing by welding is frequently used to protect selected areas with a hard layer in the millimetre thickness range. For this purpose, sintered or tube-type welding electrodes are available to produce wear resistant surface layers. Cast tungsten carbide or tungsten monocarbide are the hard constituents, while most frequently iron or an iron-based alloy acts as a binder.

Thermal spraying is applied to make thinner wear resistant surfaces. Powders for hardfacing are, for example, made of pure tungsten or more frequently tungsten monocarbide and / or cast carbide combined with cobalt, nickel, or a Ni-Cr-B-Si alloy. A large variety of grades is available to meet almost every requirement.

Chemical vapour deposition starting from tungsten halogenides or alkoxides is a less common method to provide hard, acid-resistant tungsten coatings on bearings, dies, rolls, gauges, etc.

Diamond Tools

In certain cases, even tungsten carbide tools are not hard enough. This is where the more expensive diamond tools find their application. Most of these diamond tools contain tungsten and/or tungsten carbide to improve their properties.

  • Diamond drill bits for hard rock drilling: Coarse diamonds are at the tool surface, while metal (e.g. bronze) infiltrated cast tungsten carbide forms the body of the tool. The tool shoulder is metal infiltrated coarse tungsten metal powder.
  • Diamond tools for construction, e.g. concrete and natural stone cutting: Typical tools are circular saw blades for straight cuts or tube-shaped saws for hole cutting, both of them tipped with cemented diamond segments, where tungsten monocarbide (WC) and / or cast carbide grains are frequently used to support the diamonds in the relatively soft bronze or cobalt binder.
  • Diamond or cubic boron nitride (CBN) cutting tools usually have a cemented carbide body because of its high pressure strength, equipped with a cutting edge made of sintered diamond or CBN.

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