A new hard allotropic form of carbon: Dream or reality?

Abstract An unusual phase of carbon with the fcc crystal structure, the lattice constant of which is very close to that of diamond, was reported before in a number of publications. In all the published works, the existence of fcc carbon could not be unambiguously established, as only insignificant amounts of fcc carbon in mixture with other carbon modifications were obtained so far. The present work provides for the first time clear evidence for the existence of the carbon modification with the fcc crystal structure. Thin films consisting exceptionally of fcc carbon were obtained by various methods, namely by hot-filament CVD, plasma-assisted CVD and treatment of the diamond surface in hydrogen plasmas. Results of electron diffraction, Raman spectroscopy, AES, XPS, EELS and HRTEM of the films consisting of fcc carbon clearly indicate its unique crystal and electron structure. The micro-hardness of the films of fcc carbon was found to be equal to HV 0.01 = 250 which is quite different from the hardness of all the known carbon modifications

WC-Based Cemented Carbides with High Entropy Alloyed Binders: A Review

Cemented carbides have belonged to the most important engineering materials since their invention in the 1920s. Commonly, they consist of hard WC grains embedded in a cobalt-based ductile binder. Recently, attempts have been made to substitute the cobalt using multicomponent alloys without a principal component (also known as high entropy alloys—HEAs). HEAs usually contain at least five components in more or less equal amounts. The substitution of a cobalt binder with HEAs can lead to the refinement of WC grains; it increases the hardness, fracture toughness, corrosion resistance and oxidation resistance of cemented carbides. For example, a hardness of 2358 HV, fracture toughness of 12.1 MPa.m1/2 and compression strength of 5420 MPa were reached for a WC-based cemented carbide with 20 wt.% of the equimolar AlFeCoNiCrTi HEA with a bcc lattice. The cemented carbide with 10 wt.% of the Co27.4Cr13.8Fe27.4Ni27.4Mo4 HEA with an fcc lattice had a hardness of 2141 HV and fracture toughness of 10.5 MPa.m1/2. These values are higher than those for the typical WC–10 wt.% Co composite. The substitution of Co with HEAs also influences the phase transitions in the binder (between the fcc, bcc and hcp phases). These phase transformations can be successfully used for the purposeful modifications of the properties of the WC-HEA cemented carbides. The shape of the WC/binder interfaces (e.g., their faceting–roughening) can influence the mechanical properties of cemented carbides. The most possible reason for such a behavior is the modification of conditions for dislocation glide as well as the development and growth of cracks at the last stages of deformation. Thus, the substitution of a cobalt binder with HEAs is very promising for the further development of cemented carbides