UDC 541.16
S. F. Matar1, V. L. Solozhenko2, *
1Lebanese German University (LGU), Sahel Alma, Jounieh, Lebanon
2LSPM–CNRS, Université Sorbonne Paris Nord, Villetaneuse, France
*vladimir.solozhenko@univ-paris13.fr
First-principles search for new ultrahard high-density carbon allotropes: hexagonal C6, C9, and C12 (pp. 3-13)
Hexagonal carbon allotropes C6, C9, and C12 with qtz, sta, and lon topologies, respectively, were predicted based on crystal chemistry and first-principles calculations. The new allotropes are mechanically (elastic properties) and dynamically (phonons) stable phases and are characterized by ultrahigh Vickers hardness, exceptionally high for qtz C6 and C12, close to the previously studied qtz C3. The electronic band structures of all new allotropes exhibit behavior from semiconducting to insulating. lon C12 can be considered as a new “superlonsdaleite”.
Keywords: carbon allotropes, first-principles calculations, density, hardness, phonons, insulators.
UDC 534.631:539.32:539.42:658.562
L. M. Devin*, M. P. Bezhenar, S. V. Rychev
V. M. Bakul Institute of Superhard Materials, NAS of Ukraine, Kyiv, Ukraine
*ldevin350@gmail.com
Features of measuring the elastic modulus and decrement of vibrations of polycrystals of superhard materials by the dynamic method (pp. 14-21)
The resonant frequencies of natural vibrations of disk-shaped samples were determined depending on the elastic modulus and sample size. The influence of the sample mounting location on the accuracy of determining the elastic modulus and decrement of vibrations of batches of samples of polycrystals from cubic boron nitride and diamond was assessed. All considered variants of sintered polycrystals can be divided into three groups depending on the diamond powder content. The properties (elastic modulus, decrement of vibrations, sound velocity, Q factor) of each of these groups of polycrystals are different.
Keywords: cubic boron nitride, vibration decrement, Q factor, elastic modulus
UDK 666.3:539.422.25
Junlong Sun1, Weifu Zhao1, Zhizhen Li2, Bin Li3, Changxia Liu1, *
1School of Transportation, Ludong University, Yantai, Shandong Province, P. R. China
2Yantai EDDIE Ruineng Superhard Tools Co., Ltd, Yantai, Shandong Province, P. R. China
3School of Intelligent Manufacturing, Luoyang Institute of Science and Technology, Luoyang, P. R. China
*liuchangxia2013@163.com
Effect of Al2O3 and Yb2O3 additives on mechanical characteristics and thermal shock behavior of zirconia composites manufactured by spark plasma sintering (pp. 22-34)
ZrO2–Y2O3 with different with Al2O3–Yb2O3 additives was manufactured by spark plasma sintering (SPS). The effect of Al2O3 and Yb2O3 additives on the mechanical properties, phase transformation, thermal shock resistance and microstructure of ZrO2–Y2O3 composites was investigated. The addition of Al2O3 and Yb2O3 contributed to the enhancement of the phase transformation and densification of ZrO2–Y2O3 composites manufactured by the SPS method. The ZrO2–Y2O3 composites had optimal comprehensive characteristics with Al2O3 and Yb2O3 contents of 10 and 4% (by weight), respectively. Thermal shock resistance (TSR), hardness, fracture toughness, strength, and relative density can be achieved at 344 °C, 13.6 GPa, 5.7 MPa m1/2, 900 MPa, and 99.5%, respectively. The combination of grain size reduction, fracture mode modification, density increase, and phase transformation contributed to the improvement of TSR and mechanical properties of ZrO2–Y2O3 composites fabricated by SPS.
Keywords: zirconium, spark plasma sintering, Al2O3, mechanical properties, thermal shock behavior.
UDC 621.9.01:519.233.5
Manojit Das, Soumya R. Parimanik, Trupti Ranjan Mahapatra*, Debadutta Mishra, Dilip Kumar Sahu
Department of Production Engineering, Veer Surendra University of Technology, Burla, Odisha, India
*trmahapatra_pe@vssut.ac.in
Characterization, Machinability Modeling and Machining Performance Improvement of Graphene-Reinforced Aluminum Metal Matrix Composite Using Response Surface Methods Based on Central Compositional Plan and Utility (pp. 35-64)
The machinability of graphene-based aluminum metal matrix composite (AMMC) was investigated using a polycrystalline diamond tool with carbide insert in a dry environment and compared with that of pure aluminum. AMMKs were synthesized by graphene particle reinforcement (0, 0.5, 1, 2 and 3 wt.%) using a stir casting process and their density, tensile, compressive, microhardness and morphological properties were determined. The reaction optimization is performed to minimize two surface roughness factors (Ra and Rz), reduce energy consumption and vibration (average acceleration). The central compositional design (CCP-based) response surface method (CSD) and subsequent higher-order response regression modeling of the actual process results were implemented for experimental design. The characteristics and processability of AMMKs containing more than (1, 2 and 3) wt.% graphene were first investigated together with the optimization of many characteristics (Ra, Rz, power consumption and vibration). The optimal combination of process parameters that leads to simultaneous minimization of all feedbacks is also obtained using the utility concept, compared to those obtained using the desirability approach in the response surface method and verified by conducting a confirmatory test. Improvements in surface roughness values (7.85 and 36.26 % for Ra and Rz, respectively) and average acceleration (18.09 %) were observed using the utility method compared to the CCP-based MPV. Improved output results were also observed compared to the machinability of pure aluminum.
Keywords: machinability, graphene, aluminum metal matrix composite, central composition plan, utility method, analysis of variance.
UDC 621.9.025.77:615.46:616.728
S. V. Sokhan*, V. V. Vozny, V. G. Sorochenko, M. P. Gamanyuk
V. M. Bakul Institute of Superhard Materials, NAS of Ukraine, Kyiv, Ukraine
*svsokh@gmail.com
Diamond grinding of ceramic balls with circular feed (pp. 65-79)
For diamond grinding of ceramic balls made of silicon nitride with circular feed, the results of an experimental study of the influence of the processing mode on the wear of the surface of the diamond wheel and the accuracy of the shape of the balls are presented. The indicators of the wear of the wheel surface were the angle of inclination of the working surface in the radial direction and the coefficient of curvature, and the accuracy of the shape of the polished balls were the inconstancy of the ball diameter and the form factor of the circular pattern. The observed effects are described by adequate linear dependencies of the inclination angle and the curvature coefficient on the feed rate of the workpieces, the inconstancy of the ball diameter on the rotation frequency of the circle, and the form factor – on both parameters. Combinations of processing mode factors within the studied range of changes have been determined, which are the basis for further optimization of the values of the specified indicators.
Keywords: ceramic balls made of silicon nitride, diamond grinding, circular feed of workpieces, discrete feed of the cutting wheel, feed rates of workpieces and rotation of the circle, wear of the wheel, inconstancy of the ball diameter, form factor of the ball circular shape.
UDC 621.921
V. V. Smokvina, V. I. Lavrinenko, G. D. IlnitskaV. M. Institute of Superhard Materials Bakulya NAS of Ukraine, Kyiv, Ukraine
*v.smokvyna@gmail.com
**lavrinen52@gmail.com
***gil-ism@ukr.net
Defectiveness of low-strength synthetic diamond grains – a disadvantage and a positive in the case of their use in a grinding tool (pp. 80-91)
The characteristics of low-strength synthetic diamonds (AC6–AC32) used in diamond grinding processes, which have high roughness and porosity, the presence of impurities and inclusions, are studied, it is shown how such indicators affect the physical and mechanical properties of diamonds. The possibilities of using defective low-strength synthetic diamonds are considered. It is proven that their defectivity can be a positive characteristic when used in a grinding tool – it is the presence of impurities and inclusions in diamonds together with their natural porosity that can improve the strength index due to additional heat treatment and increase the retention of grains in the bonding material of the grinding wheel. The boundary conditions for the strength index of diamond grains are determined, where the presence of defects is a positive characteristic. The parameters of the defectivity of diamond grains in the event of a change in their strength index are given and it is shown which type of defectivity can increase the performance of diamond wheels.
Keywords: synthetic diamonds, porosity, roughness, impurities and inclusions, strength index of diamond grains, physical and mechanical properties.
UDC 548.211
V. M. Kvasnytsia
Institute of Geochemistry, Mineralogy and Ore Formation named after M. P. Semenenko, NAS of Ukraine, Kyiv, Ukraine
kvasnytsya@ukr.net
Main morphological varieties of diamond cubes (pp. 92-97)
Two main varieties of cubic crystals of natural diamond and the microtopography of their faces are characterized and their difference from cubic crystals of artificial diamond is shown. The features of the morphology of cubic diamond crystals are determined by their growth mechanisms.
Keywords: diamond, crystal morphology, cubic crystals, microtopography, growth mechanism.