Applications of transition metal carbides: engineering

However, TMCs have an important drawback relative to engineering applications: low ductility at room temperature. Below 1070 K, these materials fail in a brittle manner, while above this temperature they become ductile and deform plastically on multiple slip systems much like fcc metals. This transition arises from the combination of a temperature-dependent yield stress and relatively temperature-independent fracture stress. Below the transition temperature, the stress required to fracture (fracture stress) is lower than that required to move dislocations (yield stress), and vice-versa.

Circular saw blade with WC inserts

Cemented carbides

TMCs are not only brittle at room temperature; they are also difficult to manufacture. For engineering applications, the hard carbides are therefore cemented by a ductile metal binder, usually Co or Ni (hence the name cemented carbides). Additions of binder metal in the range of 5-20 wt% increase the toughness of the tools without seriously reducing hardness, rigidity, or compressive strength.

The first cemented carbides to be produced in the early 1920s were WC with Co binders, used in dies employed to draw tungsten wire filaments. Since then, WC-Co carbides have been modified by adding Ti, Ta or Nb and the resulting allows are employed in metal cutting, mining, construction, rock drilling, metal forming, structural components, wear parts and other applications. These applications exploit, to varying degrees, the unique combination of hardness, toughness, compressive strength, rigidity, abrasion and corrosion resistance, and resistance to thermal shock offered by cemented carbides.

Coated carbides

TMCs are also used as coating materials over WC-Co based alloys for metal cutting applications. For instance, thin coatings (2-20 μm) of TiC are applied to the cemented carbide tools through chemical or physical vapor deposition to suppress various tool wear processes such as crater wear, flank wear, depth-of-cut notching, or built-up edge. This coating extends tool life of cemented carbides and improves their metal cutting productivity.

WC inserts for metal cutting

Metal-forming applications

The high compressive strength, good abrasion resistance, high elastic modulus, good impact and shock resistance, and ability to take and retain excellent surface finish by cemented carbides makes them particularly useful in metal-forming applications, especially in the case of WC due to its high fracture strength. In the wire-drawing industry, cemented carbides with high Co contents are used in drawing tubes, rods and bars.

Cemented carbides have also replaced hardened alloy steel rolls in the production of hot-rolled steel rods, allowing for closer dimensional control, truer roundness, improved rod finish, non-galling tendency, and increased delivery speeds. They are also well suited for the cold reduction and finishing of strip products in which rigidity and dimensional stability are important. Moreover, their high abrasion resistance and edge strength make them ideal for use as slitter knives for trimming steel cans and stainless and carbon steel strips, cutting abrasive materials in the paper, cellophane and plastics industries, and for slitting magnetic tapes for audio, video, and computer applications. Finally, their high compressive strength and deformation resistance make them practical for use in cold-forming equipment such as punches and dies.

Structural components

Fluid-handling components

Transportation and construction

Mining and drilling

Cemented carbides also play an important role in the recovery of metallic ores and nonmetals by underground or open-pit mining practices, the recovery of minerals such as coal, potash, and trona, and in drilling for oil.

Diamond cutting