arXiv subjects

E. A. Lantcev

Publications and source records attributed to E. A. Lantcev.

3 recordsLinked to original sources

arXiv2026

Effect of the parameters of bimodal microstructure on the mechanical properties of alumina: A case of sintering regime effects

The effect of sintering regimes on the density, microstructure parameters, and mechanical properties of Al2O3 and Al2O3 + 0.25%MgO ceramics has been investigated. The ceramics were sintered in three regimes: Regime I - heating at a constant rate (2.5, 5, 10, 20 C/min) up to the temperature T=1650C; Regime II - heating with a varied heating rate up to 1565C with the duration corresponding to sintering at the heating rate of 10 C/min in Regime I followed by a three-fold decrease in the shrinkage rate; Regime III - two-stage sintering: heating according to Regime II up to the temperature T1+1550C, then lowering the temperature down to T2 = 1300-1500C and holding for 3 h at the T2. The sintering regimes were chosen so that the ceramics had the relative density of 97-99% and a bimodal distribution of the microstructure parameters. The Al2O3 and Al2O3 + 0.25%MgO ceramics obtained in Regimes I-III had a microstructure with abnormally large grains in a fine-grained matrix. The sizes and volume fractions of the large grains depended on the sintering regime. Most abnormally large grains had elongated shapes that leads to deviations in the crack propagation trajectories from the straight line. The optimal parameters of the bimodal microstructure parameters distribution providing enhanced mechanical properties of the ceramics (hardness, indentation fracture toughness, ultimate strength) have been determined.

cond-mat.mtrl-sci↗

arXiv2026

Low-temperature Spark Plasma Sintering of fine refractory composite powders core-shell: A case of the powders W@Ni

The mechanisms of fast low-temperature Spark Plasma Sintering (SPS) of W + 10% wt. Ni powders were investigated. The powder compositions were obtained in two methods: (i) by mixing W and Ni powders in a specified ratio (hereinafter referred to as W + Ni); (ii) by Ni deposition on the surface of submicron W particles allowing the formation of particles with a core W - shell Ni structure (hereinafter referred to as W@Ni). To reduce the concentrations of oxygen and oxides, the powders were annealed in hydrogen. The solid-phase sintering was performed at various temperatures (1000-1150°C), pressures (40-80 MPa), heating rates (50-500°C/min), and isothermal holding times (0-20 min). The sintering temperatures corresponded to the onset of intense dissolution of W in Ni. The samples had high relative density and small grain sizes. The activation energy of SPS of the mixed powders was close to the one of the grain boundary diffusion. The key mechanism for the compaction of W@Ni particles in the SPS process is Coble creep. The increasing of the sintering temperature was shown to lead to an increase in the solubility of W in Ni and, consequently, to an increase in the number of secondary Ni4W particles formed during cooling down. The grain growth has a minor effect on the mechanical properties of the W alloy compared to the changes in its phase composition.

cond-mat.mtrl-sci↗

arXiv2022

Low-temperature creep of binderless tungsten carbide with different grain sizes

The creep mechanism in the compression testing of the tungsten carbide with different grain sizes has been studied. The WC samples with high density (96.1-99.2%) were obtained by SPS from nano-, submicron, and micron-grade WC powders. The samples had a coarse-grained (CG) surface layers of ~0.3 mm in thickness and ultrafine-grained (UFG) central parts consisting of WC with a small fraction of W2C. The creep tests were conducted in two regimes: (Mode #1) holding at different temperatures (1300-1375C) at 70 MPa; (Mode #2) tests at different stresses (50, 70, 90 MPa) at 1325C. Tests in Mode #1 were done to determine the effective creep activation energy Qcr while tests in Mode #2 - to determine the coefficient n in the power law creep equation. The increasing of the fraction of the W2C particles from 1.7 up to 4% was found to result in a decrease in the Qcr from 17.5 down to 13 kTm. The coefficient n equals to 3.1-3.7. The Qcr in the WC sintered from nanopowders was shown to be 31 kTm. This value is 1.5-2 times greater than the Qcr in the UFG samples obtained by SPS from commercial powders. The increased fraction of the W2C formed when sintering the nanopowders with increased adsorbed oxygen concentration was suggested to be one of the origins of the increase in the Qcr when testing the UFG samples. The mechanical removing of the CG layers from the surfaces of the tungsten carbide sample was shown to result in an accelerated creep, insufficient decrease in the Qcr and coefficient n to 2.5-2.6. The creep rate of the samples was suggested to be determined simultaneously by the creep process in the CG surface layers and the creep process in the UFG central parts of the samples. The creep rate in the surface CG layers is determined by intensity of carbon diffusion in the WC crystal lattice while the creep rate in the UFG central parts - by the intensity of grain boundary diffusion.

cond-mat.mtrl-sci↗