Vol 38, No 5 (2016)

A model of the indentation using conical and pyramidal indenters has been proposed, in which not only a sample but the indenter as well are elastoplastically deformed and their materials obey the Mises yield condition. These conditions are characteristic of the measuring of diamond hardness through a diamond indenter. The model that has been proposed generalizes and refines the known simplified Johnson’s model, which uses an elastically deformed indenter. The proposed model makes it possible to determine approximately the sizes of elastoplastic zones in the indenter and sample, the effective apex angle of the loaded indenter and effective angles of the indenter and imprint after unloading. Based on this model a procedure of the determination of the sample and indenter yield strengths (Y_s and Y_i, respectively) has been developed, in which the relations that use the experimental values of the effective angle of the sample imprint and measured values of the Meyer hardness, HM (mean contact pressure) are added to theoretical relations of the indentation model. The developed computational procedure was applied in indentation experiments on synthetic diamond at the temperature 900°C (at which diamond exhibits a noticeable plastic properties) using natural diamond pyramidal indenters having different apex angles. According to the proposed model, the stress-strain states of samples and indenters have been investigated and their yield strengths and plasticity characteristics were defined. The stress–strain curve of the diamond in the stress-total strain coordinates has been constructed. The strain hardening of diamond was also studied.

Structural mechanical and thermal properties of refractory carbides have been investigated using the Realistic Interaction Potential Approach (RIPA) model. The study has been extended to mixed crystals of Hf_xTa_1–xC (0 ≤ x ≤ 1) and Zr_xNb_1–xC (0 ≤ x ≤ 1) alloys and the effect of composition on structural and elastic properties are investigated. Phase transition pressure and associated volume collapses (ΔV(P_t)/V(0)) calculated from this approach are in good agreement with available literature for the parent compounds (x = 0 and x = 1). The results for the mixed crystal counter parts are also in fair agreement with experimental data generated from the application of Vegard’s law to data for the parent compounds.

The aim of this work is to determine the mechanical and tribological behavior of V–C–N coatings deposited on industrial steel substrates (AISI 8620) by using carbon–nitride coatings as a protective materials. The coatings were deposited on silicon (100) and steel substrates via magnetron sputtering and by varying the applied bias voltage. The V–C–N coatings were characterized by X-ray diffraction (XRD), exhibiting the crystallography orientations (111) fcc for V–C–N conjugated by VC (111) and VN (111) phases and (200) fcc for VCN conjugated by VC (200) and VN (200) phases. X-ray photoelectron spectroscopy (XPS) was used to determine the chemical composition of metallic carbon–nitride materials. Atomic force microcopy (AFM) was used for determination of the change in grain size and roughness with deposition parameters. By using nanoindentation, pin-on-disk, and scratch test curves, it was possible to estimate the hardness, friction and critical load of V–C–N surface material. Scanning electron microscopy (SEM) was performed to analyze morphological surfaces changes. Mechanical and tribological behavior in VCN/steel_[8620] system, as a function of a bias voltage deposition, showed an increase of 58% in the hardness, and reduction of 39% in the friction coefficient, indicating thus that the V–C–N coatings may be a promising material for industrial applications.

The authors study the intensity of cutting workpieces of hardmetals, polycrystalline cBN-based material and polycrystalline diamond-on-hardmetal compacts in the following operations: waterjet cutting, laser cutting, liquid-cooled laser cutting, and laser–jet cutting. Special features of cutting two-layered composites that comprise a polycrystalline diamond layer on a hardmetal substrate are analyzed. The paper demonstrates the efficiency of the hybrid machining process that combines the laser–jet and waterjet technologies and provides an effective cutting of workpieces to a required profile.

The paper gives theoretical substantiation of the phenomenon of a circular shape of a scratch cross-section averaged over a set of cuts produced by far-from-round tips of diamond grains of electroplated dressing tools that work on the abrasive material of grinding wheels. This cross-sectional shape is identified as an effective shape of the grain that produces the scratch. Information on the scratch parameters and their relationship with the diamond grain size in the tool is needed for calculating individual and total cross-sections of cuts, dressing forces, and surface roughness of workpieces upon grinding with abrasive wheels dressed by a diamond roll.

The paper presents a new method for assessing the applicability of explosive charges for the synthesis of nanodiamonds by the oxygen balance and charge density. The recommended oxygen balance value is–35 to–60 and charge density value is 1.6 to 1.7 g/cm³.