The effect of the concentration of vanadium nitride additive (in the range from 0 to 10 wt %) on the phase formation, hardness, and fracture toughness of composite diamond-containing materials based ...on the 51Fe–32Cu–9Ni–8Sn matrix molded by cold pressing and subsequent vacuum hot pressing is investigated. It is found that the addition of 10 wt % of vanadium nitride to the 51Fe–32Cu–9Ni–8Sn composite is accompanied by an increase in the hardness from 3.86 to 8.58 GPa with a slight decrease in the fracture toughness from 5.55 to 4.76 MPa m
1/2
. Moreover, the
H
(
C
VN
) dependence has two characteristic segments that differ in the slope. The hardness increases insignificantly (from 3.86 to 5.26 GPa) in the range of 0 <
C
VN
< 4 wt %, while the second region (
C
VN
> 4 wt %) is characterized by a more substantial increase in the hardness and a more significant decrease in the grain size. It is shown that these parameters are achieved owing to the dispersion mechanism of strengthening and modification of the structure (a decrease in the mean particle size of the matrix phase, the formation of new (Fe
3
Ni)
0.5
and Cu
3
Fe
17
phases, and the precipitation of primary and secondary phases of vanadium nitride) and phase composition of the composites.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Some new data on the effect of chromium diboride additives (within a range from 0 to 10 wt %) on the phase formation and physicomechanical properties (fracture toughness, hardness, ultimate bending ...and compression strength) of composite materials based on the WC–6 wt % Co hard alloy formed by cold pressing with further vacuum hot pressing are reported. It has been revealed that the sintered samples of composites are composed of the structural phases of hexagonal WC and orthorhombic B
2
CoW
2
groups and amorphous carbon inclusions. In this case, the parameters of crystalline B
2
CoW
2
are varied depending on the CrB
2
content. It has also been established that the addition of 4 wt % of chromium diboride to the WC–6Co composite leads to a two-fold increase in the fracture toughness (from
K
Ic
of 9.8 to 14.5 MPa m
1/2
) with a slight decrease in the hardness
H
from 15.1 to 13.9 GPa and also to an increase in the ultimate bending strength
R
bm
from 2000 to 2500 MPa and the ultimate compression strength
R
cm
from 5300 to 5500 MPa. It has been shown that the mentioned parameters are attained due to the dispersion mechanism of reinforcement with transformations in the structure (a stable decrease in the average grain size of the carbide phase, the disappearance of pores in the location of the binding Co phase, the formation of inhibitor phase clusters at phase interfaces) and phase composition of the composites.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this work, the characteristics of the structure, hardness, elasticity, and cavitation resistance of the material of Ti2AlC MAX phase cathodes manufactured by hot pressing, as well as ion-plasma ...coatings deposited using these cathodes on titanium alloy Ti6Al4V, have been studied. It was found that the cathode material, which contains 83 wt. % MAX phase Ti2AlC, is characterized by a hardness of 10 GPa, a H/E value of 0.04, and low cavitation resistance. The average cavitation wear of the cathode is 4 times higher than that of the titanium alloy Ti6Al4V. It was found that the elemental and phase composition of the obtained coatings differs from the composition of the cathode. The main phase in the coatings is nanocrystalline carbide (Ti, Al) C with a cubic structure of the NaCl type. Ti0.58Al0.17C0.25 coatings deposited by ion sputtering using an arc gas plasma source are characterized by a hardness of 21 GPa. The hardness of vacuum-arc coating Ti0.65Al0.07C0.28 is closer to the hardness of the cathode – 13 GPa, which is due to the presence of α-Ti in its composition. The H/E ratio of the coatings is 1.5 times higher than that of the cathode, which is a prerequisite for high cavitation resistance. The average rate of cavitation wear of vacuum arc coating Ti0.65Al0.07C0.28 is 1.5 times lower than that of the vacuum arc coating TiN and 3 times lower than that of the uncoated Ti6Al4V alloy.
Analysis of XRD patterns by Rietveld refinement has been shown that the main phase of superconducting MgB2-based bulk materials (with high level of superconducting characteristics) has AlB2 type ...structure and near MgB1.8-1.68O0.2-0.32 stoichiometry. The materials demonstrated the critical current densities up to 0.9 - 0.4 MA/cm2 jc (at 0 - 1 T, 20 K); up to 15 T Bc2 (at 22.5 K) and Birr (at 18 K). The ab-initio simulation confirmed (1) benefits in binding energy and enthalpy of formation if stoichiometry of the solid solution is near MgB1.75O0.25; (2) energetic advantage in case if impurity oxygen present only in each second boron plane of MgB2 cell while the first boron plane of the same cell stays pristine and location of substituted oxygen atoms in the nearby positions. Besides, the results of ab-initio modeling allow explanation of the tendency towards segregation of O-impurity in MgB2 structure during synthesis or sintering, and formation of Mg-B-O inclusions or nanolayers (with MgO type of structure) which effect pinning. Calculated transition temperatures, Tc, for MgB1.75O0.25 occurred to be 23.3 K, while for MgB2 it was 21.13 K only. Experimental Tc of the bulk materials was 35.7-38.2 K.
Magnesium diboride-based material high-pressure synthesized at 2 GPa and 800 deg C for 1 h from Mg and B (taken in the stoichiometry ratio of MgB2) with addition of 2-10 wt.% of Ti demonstrated the ...critical current density (jC) higher than 100 kA/cm2 at 20 K up to 3 T and at 33 K in 0 T field. At 20 K the critical current density higher than 10 kA/cm2 was observed up to 5 T field. In the magnetic fields up to 2 T high-pressure synthesized MgB2 (with 10% of Ti) at 20 K has a critical current density comparable to that of Nb3Sn at 4.2 K. XRD patterns of magnesium diboride with Ti addition exhibited no evidence of unreacted titanium and only one compound with titanium was identified, namely, titanium dihydride TiH2 (or more strictly TiH1.924). The sample with the highest critical current density and the irreversibility field in the temperature range of 25-10 K contained some amount of rather homogeneously dispersed pure Mg and high amount of Mg-B inclusions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The process of coating deposition by sputtering a target based on the MAX phase Ti2AlC using a gas plasma source has been studied. It has been shown that the MAX phase of Ti2AlC refers to ...hard-sputtering materials. With an increase in the sputtering energy of Ar+ ions from 400 to 1200 eV, the sputtering coefficient of the target based on the MAX phase increases from 0.2 to 0.7 atom/ion. The obtained values are 1.5 times lower than the sputtering coefficients of the target from titanium. Phase transformations occur on the target surface and are associated with the decay of the MAX phase and the selective sputtering of lighter elements due to the bombardment by Ar+ ions. It was found that the composition of the deposited coatings is significantly affected by the magnitude of the bias potential on the substrate. With increasing potential in the range from 50 to 200 V, the relative aluminum content in the coatings drops sharply, in favor of titanium from Ti:Al 3.5:1 to Ti:Al 48:1. Regardless of the composition, a solid solution (Ti, Al)C is formed in the coatings with a cubic crystal lattice of the NaCl type, a crystallite size of 10-15 nm and an axial type texture. The MAX phase Ti2AlC was not detected in the coatings. Received coatings have high hardness and Young's modulus, which increase with decreasing aluminum concentration in the ranges of 21-30 GPa and 290-340 GPa.
Abstrac
t—Some comparative nanoindentation results were presented for the Ti
3
AlC
2
MAX phase (nanolayered material), the (001) plane of a LiF single crystal (elastoplastic material), and the PTFE ...polymer (viscoelastoplastic material). Using quasi-static nanoindentation, the hardness and elastic modulus of specimens were determined, and significant elastic energy dissipation was revealed the for Ti
3
AlC
2
MAX phase under cyclic loading (as typical for some other nanolayered materials, such as graphite and high-temperature superconductors). To determine the viscoelastic characteristics for the MAX phase, the indentation depth change was measured in 60 s after fast indenter unloading. The relaxation time was determined for the MAX phase for the first time. In addition, fast unloading also made it possible to separate the components (elastic, viscoelastic, and plastic) of strain upon nanocontact for these materials. Although the share of viscoelastic strain in the total strain upon contact was negligible (~0.1%) for LiF, it was much higher for the Ti
3
AlC
2
MAX phase and the PTFE polymer and equal to ~1 and ~17%, respectively.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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