SUMMARY. There is a general trend in the modern carbide industry to produce WC-Co materials comprising extremely fine grains with the target of achieving the range of nanomaterials. On this ground near-nano cemented carbides and cemented carbides with nanograin reinforced binder were developed and implemented in industry on a large scale at Element Six Hard Materials.

 

The trend of decreasing the WC mean grain size in WC-Co cemented carbides resulted in the development of cemented carbides with WC grain size close to the nanoregion (100 nm or less). Such cemented carbides with WC mean grain size of about 200 nm are designated in the literature as “near-nano cemented carbides”. Very fine, uniform und inactive WC powders are needed for fabrication of such cemented carbides. Only recently, near-nano WC powders characterised by the low activity with respect to re-crystallisation during liquid phase sintering were developed. Two novel near-nano carbide grades on the basis of the near-nano WC powders were recently developed and implement in industry on a large scale. The near-nano grades are characterised by a high combination of hardness, wear-resistance and fracture toughness. For example, the hardness of the near-nano grade with 10% Co for wear parts is above 20 GPa, fracture toughness is nearly 9.5 MPa m^1/2 and wear-resistance is roughly 6 times higher than that of a conventional ultra-fine grade with 10% Co. Nevertheless, the near-nano cemented carbides cannot substitute coarse- and ultra-coarse carbide grades in applications of mining and construction, the reasons of which will be discussed in detail.

Novel ultra-coarse cemented carbides with nanograin reinforced binder with the brand name Master Grades® were recently developed and implemented in industry on a large scale. Their microstructure consists of rounded WC grains with thick and uniform interlayers of the Co-based binder among them, which allows lower internal stresses and high fracture toughness to be obtained. The Co-based binder of the Master Grades is reinforced and hardened by nanoparticles of the θ-phase (Co₂W₄C), the mean grain size of which is significantly below 10nm. As a result, the binder nanohardness of the Master Grades is equal to 10.2 GPa, whereas that of conventional grades without nanograin reinforcement is equal to only 7.5 GPa. This leads to a significant increase in wear-resistance and some increase in TRS of the Master Grades in comparison with conventional grades with the same Co content and similar WC mean grains without sacrificing the fracture toughness. Tool lifetime of road-planing picks and mining picks with inserts of the Master Grades is prolonged by a factor of up to 3, wich is accomplished by a noticeable decrease in a number of premature failures during operation. Results on TEM and HRTEM of the binder of the Master Grades will be presented.