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The effect of medium fluences (from 1019 е/cm2 to 1020 е/cm2) of fast electron irradiation or the change in the praseodymium concentration in the range 0.0 ≤ z ≤ 0.5 on the excess conductivity of optimally oxygen-doped YBa2Cu3O7–δ single crystals has been investigated. Irradiation leads to the appearance of a significant number of defects that cause a decrease in anisotropy, an appreciable increase in phonon scattering, reduction of Tc, and broadening of the superconducting transition. Under the conditions specified, the temperature dependence of electrical resistivity is approximated with high accuracy by the charge carriers' scattering on defects and phonons, and fluctuating conductivity in the Lawrence–Doniach model. It was determined that at fluences 0 ≤ Ф ≤ 6.5⋅1019 е/cm2, the value of the transverse coherence length ξс(0) increases with an increase of Ф by about three times or more than four times as the content of praseodymium in the sample increases to z ≈ 0.42. In both cases, the 2D–3D crossover point shifts upward in temperature. In contrast to the case of irradiation with low fluences (Ф ≤ 1019 е/cm2) or doping with praseodymium up to concentrations z ≤ 0.39, irradiation with medium fluences and doping with praseodymium at higher concentrations leads to a nonmonotonic dependence of the transverse coherence length ξс(0) on the irradiation fluence, with characteristic maxima at Ф ∼ (7–8)⋅1019 е/cm2 or z ≈ 0.42, which may be due to the general suppression of the superconducting characteristics. [ABSTRACT FROM AUTHOR]

The study investigated the wear rate dependences of diamond-impregnated drill bits consisting of composite diamond-containing materials (CDMs): specifically, 25Cdiamond–70.5WC–4.5Co and 25Cdiamond–68.62WC–4.38Co‒2ZrO2. These materials were fabricated via spark plasma sintering at temperatures ranging from 20 to 1350°C under a pressure of 30 MPa for 3 min. Testing was conducted under rotational speeds and axial load conditions typical for granite drilling. It was demonstrated that incorporating 2 wt % of ZrO2 nanopowder into the composition of 25Cdiamond–70.5WC–4.5Co resulted in a threefold reduction in wear rate. The highest wear resistance of these diamond-impregnated drill bits was observed at rotational speeds of 250 rpm and axial loads of 900 kg, as well as at 750 rpm and 1250 kg axial load. Comparatively, the enhanced wear resistance of diamond-impregnated drill bits made from 25Cdiamond–68.62WC–4.38Co‒2ZrO2, in contrast to those made from 25Cdiamond–70.5WC–4.5Co, can be attributed to factors such as finer grain size, higher relative density, improved strength under compression and bending, increased fracture toughness, and the formation of strong bonding between diamond grains and the hard-alloy matrix. These findings, combined with the fine-grained structure of the hard-alloy matrix and high diamond retention, indicate that these diamond-impregnated drill bits have potential for application in developing new tools with superior operational properties for drilling hard rock formations. [ABSTRACT FROM AUTHOR]

New data on the effect of a ZrO2 nanopowder additive (from 0 to 10 wt %) on phase formation and structural transformations in the hard-alloy matrix in the region of destruction under impact loading and on diamond retention in composite diamond-containing 25Сdiamond–70.5WC–4.5Co materials formed by spark plasma sintering are presented. The sintered initial 94WC–6Co composite consists of the hexagonal WC phase with unit cell parameters a = 0.2906 nm and с = 0.2837 nm, the cubic Co3W3C phase (а = 1.1112 nm), and the hexagonal graphite phase. The sintered composites with ZrO2 content from 0.5 to 10% is composed by the WC and Co3W3C structural phases, amorphous carbon, and the tetragonal ZrO2 phase (а = 0.36019 nm, с = 0.5174 nm). It has been shown that, when the ZrO2 content is increased, the sizes of phase components and average microstrains are more rapidly decreased in directions с and а of the 94WC–6Co composite. The addition of ZrO2 to the 25Сdiamond–70.5WC–4.5Co composite improves diamond retention. In the sintered composites, diamond retention is improved due to that they have a higher content of the tetragonal ZrO2 phase, which provides the transformational mechanism of strengthening in the hard-alloy matrix material via its structural transformations into a denser one and the formation of a more fine-grained matrix structure with thin interlayers of cobalt bonds between WC grains. [ABSTRACT FROM AUTHOR]

The effect of the addition of ZrO2 micropowder (in the range from 0 to 10%) on the structural changes of the hard alloy matrix in the area of fracture as a result of impact loading of a sample of composite diamond-containing material (DCM) 25Сdiamond–70.5WC‒4.5Co wt % was studied, formed by the method of spark plasma sintering in the temperature range from 20 to 1350°С at a pressure of 30 MPa for 3 min. It was found that in the DCM sample without ZrO2 additive, the structure of the hard alloy matrix has the appearance characteristic of brittle fracture, which is evidenced by the smooth relief of the fracture surface. In this case, the destruction of the DCM sample occurs by chipping of the components of the hard alloy matrix, which leads to a decrease in its wear resistance. The introduction of the ZrO2 additive in the amount of 4% into the composition of DCM causes a change in the structure of the fracture surface. On the fracture surface of the carbide matrix of the DCM sample, nanopores with a structural size of ~100–500 nm are formed as a result of viscous (pitting) fracture. At the same time, in addition to the formation of dimples on the fracture surface of the hard alloy matrix, a highly developed relief is simultaneously formed on the surface of the diamond grain, which is evidence of improved diamond retention and increased wear resistance of the composite. With a further increase to 10% of the ZrO2 additive in the DCM composition, a more pronounced microrelief with the presence of deep dimples and microcracks is formed on the fracture surfaces of the hard alloy matrix and diamond grain. It is proposed to use the type of relief of the fracture surface of sintered DCM samples during impact fracture at room temperature as an assessment of the characteristics of the strength of diamond retention. [ABSTRACT FROM AUTHOR]

The structure and mechanical properties (hardness Н, elasticity modulus Е, estimative parameters for determining the resistance to elastic H/E and plastic Н3/Е2 deformations, ultimate bending Rbm and compression Rcm strength) of diamond-containing Сdiamond–WC–Co–CrB2 composite materials (DCM) formed by spark plasma sintering and the ability of their hard-alloy matrix to retain diamond grains from falling out have been studied as a function of the chromium diboride content (within a range from 0 to 10 wt %). It has been established that the addition of CrB2 at a concentration of 4 wt % to 25Cdiamond–70.5WC–4.5C leads to an increase in the ultimate bending Rbm (from 2040 ± 20 to 2375 ± 50 MPa) and compression Rcm (from 5100 ± 30 to 5650 ± 70 MPa) strengths and in the estimative parameters for determining the resistance to elastic H/E (from 0.043 to 0.051) and plastic Н3/E2 (from 0.062 ± 0.0040 to 0.080 ± 0.0070 GPa) deformations. A further increase in the CrB2 concentration (to 10 wt %) in a specimen leads to a gradual decrease in the ultimate bending Rbm (to 1840 ± 80 MPa) and compression Rcm (to 5100 ± 100 MPa) strengths with a growth in Н/E (to 0.054) and Н3/Е2 (to 0.088 GPa). As a criterion for estimating the hard-alloy matrix ability to retain diamond grains from falling out, it is proposed to use the state of the surface relief of fracture in a DCM specimen. Under such a condition, the relief surface of diamond is indicative of strong adhesion between diamond grains and a hard-alloy matrix. The destruction of a DCM specimen along the diamond–matrix interface indicates that the adhesion between diamond grains and a hard-alloy matrix is weak to worsens the performance characteristics of such DCMs. It has been shown that the mentioned mechanical and performance characteristics of DCM specimens can be attained by adding 4 wt % of CrB2 into DCMs to decrease the growth rate of WC grains and, as a consequence, to form a homogeneous fine-grained microstructure in their hard-alloy matrix. [ABSTRACT FROM AUTHOR]

In this work, we studied the fixation of magnetic vortices (pinning effect) on "inelastic" and "elastic" twins, whose wedge-shaped peaks in the direction of twinning do not reach the crystal surface. The effectiveness of the "elastic" twins effect as pinning centers was studied by measuring of the critical transport current Jc in single crystals YBa2Cu3O7–x. The presented experimental data indicate that the "elastic" twins boundaries are effective pinning centers of the magnetic flux lines in single crystals of the compound under study. The main pinning centers of the vortices are dislocation clusters forming at the vertices of the "elastic" twins. The dislocation lines are located in the twin plane and, if the orientation of the magnetic vortices and dislocation lines coincide, the energy of the vortices decreases, the pinning force appears, fixing their location, which ultimately leads to an increase in the critical density of the transport electric current. [ABSTRACT FROM AUTHOR]

The structure, mechanical properties (hardness H and elastic modulus E), evaluation parameters for determining the resistance of the material to elastic (H/E) and plastic (H3/E2) deformations, resistance 1/(E2/H) to abrasive wear, and the ability of the hard alloy matrix to hold diamond grains from their precipitation in the 25 wt % Cdiamond‒70.5 wt % WC‒4.5 wt % Co composite diamond-containing materials (CDMs) with different contents of ZrO2 (in the range from 0 to 10 wt %), which are formed by the spark plasma sintering (SPS) method in the temperature range of 20‒1350°C under a pressure of 30 MPa for 3 min. The initial CDMs have a coarse grained structure with weak adhesion of diamond grains to the hard alloy matrix and are characterized by low values of H/E, H3/E2, and 1/(E2H), which is the reason for the premature loss of diamond grains. The presence of ZrO2 in the composition of CDMs interferes with the processes of Oswald ripening and acts as a growth inhibitor that ensures the reduction of WC grains, the formation of strong adhesion of diamond grains to the matrix, and a substantial increase in the H/E, H3/E2, and 1/(E2H) parameters. As a result, the ability of the matrix to reliably hold diamond grains from premature loss during the CDMs operation increases. It is shown that the addition of zirconium dioxide in the amount of 10 wt % to the composition of the 25 wt % Cdiamond‒70.5 wt % WC‒4.5 wt % Co composite leads to increases in the H/E parameter from 0.043 to 0.057, in the H3/E2 parameter from 0.05 to 0.075 GPa, and in the 1/(E2H) parameter from 0.75 × 10–7 to 2.75 × 10–7 GPa–3. Moreover, signs of strong adhesion between the diamond grains and the carbide matrix in the CDMs samples are revealed. [ABSTRACT FROM AUTHOR]

The effect of medium doses (from 1019 to 1020 cm–2) of irradiation with fast electrons (energy, E = 2.5 MeV) on the excess conductivity of optimally doped Y1Ba2Cu3O7–δ single crystals has been studied. It is shown that the irradiation with electrons leads to the significant expansion of the temperature interval for the existence of excess conductivity, thereby narrowing the region of the ρ(T) linear dependence in the ab plane in the normal state. It has been established that at doses of 0 ≤ D ≤ 6.5⋅1019 cm–2, the value of the transverse coherence length ξc(0) increases with D by about 3 times and the 2D–3D crossover point shifts in temperature. In contrast to the case of irradiation with low doses (D ≤ 1019 cm–2), irradiation with medium doses leads to a nonmonotonic dependence of the transverse coherence length ξc(0) on the irradiation dose, with a characteristic maximum at D ∼ (7–8)⋅1019 cm–2, which may be related to the general suppression of superconducting characteristics. [ABSTRACT FROM AUTHOR]

The effect of the conditions of synthesis on the formation of micro- and nanoparticles of zirconium dioxide from a fluoride solution has been studied. It is shown that the finest particles are formed by precipitation from dilute solutions with a zirconium concentration of 0.02–0.04 mol/L and impurities of polyvinyl alcohol at a mass ratio of mZr : mPVC 1 : 0.1. To sinter ZrO2 nanoparticles, it is proposed to use the electroconsolidation method in a vacuum to obtain ceramics with high values of the hardness and elastic modulus. [ABSTRACT FROM AUTHOR]