The properties of an array of carbon nanostructures or a material containing its is differ from the properties of individual components. For bulk array of carbon nanostructures it is unknown to what extent the electrons of each layer participate in conductivity, the role of defects is not defined. properties. So, this work presents some answers to these questions.
The electrical and mechanical properties of nanocomposites based on carbon nanostructures has been studied. It is sown that a t a concentration of carbon nanotubes of 15-30 wt. %, the electrical resistance of the samples decreases to 1 order, while its mechanical properties change insignificantly, which is due to the transfer of free electrons from the metal to the CNT, which is comparable to the number of electrical contacts between the constituent elements of the composite and the competition between the numbers of tu nneling and ohmic contacts.
The influence of high-carbon ferrochrome on the features of structure formation and properties of chromium carbide steels based on the Fe-FKh800 system was investigated. It was shown that the optimal combination of hardness and tensile strength with sufficient crack resistance has a carbide base of 65% Fe – 35% (wt.) FKh800. A typical microstructure of sintered carbide is a metal matrix composite consisting of chromium steel of composition close to Kh17 and double carbide (Cr0.799Fe0,201) 7C3. The effect of TiB2 additive on the structure, phase composition, mechanical and tribotechnical properties of materials based on the Fe- 35 (%,wt.) FKh800 system was also investigated. Additions of titanium borides in the amount of 0.38-1.48 (% wt.) leads to some increase in hardness, noticeable increase in the flexural strength and leads to increase wear resistance of carbidosteels.
Heat-resistant composites with a layered niobium-based matrix reinforced with single-crystal sapphire fibers have been obtained. The fibers were grown from the melt by the modified Stepanov method. The composites were prepared by solid-phase technology by diffusion welding of multilayer packages of foils of the Nb–0.1% C and aluminum alloy, interlaid with sapphire fibers in layers of a suspension mixture of Nb powder. The production of fibers, their structure and strength testing procedure are described. The formation of multilayer packets, the structure and results of bending strength tests of composites are presented
The work is devoted to the development of a solid-phase technology for obtaining high-temperature layered composites from Nballoys. The following are presented: one of the options for the formation of the initial multilayer package and its diffusion welding (1), the microstructure of the obtained composites (2) and the results of testing composites (3) for strength at room temperature and temperatures up to 1350°C, taking into account the structure anisotropy, crack resistance and tests for creep with two options for processing the obtained experimental data.
The effect of TiB2 additives on the sintering temperature, structure, and mechanical properties of materials based on the Fe-FeCr800 system is investigated. It was shown that the introduction of titanium diboride additives leads to the activation of compaction and to a 50–70ºС decrease in the sintering temperature of the pressed composites based on iron. It has been studied that the addition of titanium diboride in the range of 0.38-0.74 (% wt.) provides, with a slight increase in hardness, an increase of 20-25% of the flexural strength of the composite 65Fe-35 FeCr800800 (% wt.), and also provides the formation of a multiphase, microheterogeneous structure of the matrix-filled composite type, which consists of chromium steel of the X6Cr17 type, double iron-chromium carbides M7C3, M3C and complex carboborides of the Me3(CB) type.
The influence of temperature of sintering on structure formation, phase composition, microhardness of components of powder composite 65 % wt. Fe – 35 % wt. FH800 were investigated. It has been established that the increase in the temperature of sintering from 1050 ºС to 1250 ºС leads to some increase in volumetric shrinkage, density and decrease in porosity of samples of material which was made from coarse-grained source powders of industrial production components. It was found that the sintering of green compacts in the range of 1000-1300 ºС causes significant changes in the chemical and phase composition of the carbide component of the composite, which are described by a series of phase transformations: M7C3 → M3C (1000-1150 ºС) → M7C3 (1200 ºС) → M3C (1250-1300 ºС)
Although molding of thermoplastics is very productive method of machinery manufacturing, pure plastics are almost not used in so much quantity. Particle reinforced composites are more popular, because presence of solid inclusions reduces volume of organic matrix and usually improve strength and stiffness. Final properties are strongly influenced by manufacturing process which affects inner material structure. In composites where fibers are continuous in one direction or placed in layers, i.e. the fibers do not end inside the composite and it`s length is close to the dimension of machinery parts, elastic [1] [2] and thermal properties [7] can be predicted quite easily by Halpin-Tsai equations or derived simplified methods [2] with high accuracy. This paper is focused on prediction of density and material stiffness of composites, which are reinforced with very short glass fibers in thermoplastic matrix. In the first part we define the field of problem. Then we present simplified analytical calculus in compare to finite element method. We focus on ABAQUS 2018 and its features, which can be used for solving those problems. Estimation approaches such as representative volume element method and mean field homogenization are also studied. After this presented methods are confronted with selected material datasheet of Ultramid® A3WG6 [9] and Zytel® 70G35HSLRA4 [12] composite material. The effect of fiber randomization on material stiffness is introduced [4]. At the end of thesis we use previously calculated material data for modal analysis of real parts which are made from molded thermoplastic with short glass as well.
It was analyzed the methods of constructions the matter with maximal of packing coefficient when the objects consist of the particles with forms either spheres or rods or plates. It was calculated the relations the partial size for relating of maximal packing coefficient. As examples of objects with coefficient of packing theirs particles we look on abrasive materials and products of the powder metallurgy and solid fuel etc.
The results of the estimation for the influence of titanium diboride content in the initial powder mixture on the basic mechanical properties at the tests on tension and compression are presented. It is shown that the porosity of sintered at 1250 0C preforms from TiH2-TiB2 powder mixture increases with increasing of titanium diboride content in the initial charge, which is due to the manifestation of the Frenkel effect at sintering. The values of tensile strength, hardness and elastic modulus, despite some porosity growth of the sintered alloy, increase with the addition of 5 % of TiB2 powder, while increasing the content of the high modulus component in the mixture to 10 % leads to decrease in the level of these characteristics. The plasticity of sintered alloys monotonically decreases with increasing of the boride component content. At compression tests, the yield point and the compressive strength increase monotonically with increase in TiB2 content, despite the increase in porosity of the latter, due to a significantly lower effect of porosity on the value of the resistance to deformation in compression compared with tension. The use of hot forging of sintered powder preforms leads to increase of strength properties and hardness of the composites.
The investigation of the interface connection area of the three-layer tube "steel / vanadium alloy / steel" after different deformation-heat treatments was performed. Furthermore, a qualitative and quantitative analysis of the structure of the three-layer material were conducted, including analysis of the contact area of the steel and the vanadium alloy and the diffusion layer between them was obtained. The analysis of the microstructure and mechanical properties (microhardness, ultimate tensile strength, yield strength and elongation) of three-layered material has been carried out.
The feachures of structure and phase formation of TiC hardened Fe-based alloy at in-situ thermal synthesis from mixtures of TiH2, Fe, graphite and Ni powders had been investigated. It was shown that after synthesis at 1200 0С the structure of the alloy is a skeleton of titanium carbide grains of various shapes and sizes from 1 to 20 µm cemented with Fe-based binding substance mostly located around the titanium carbide grains. The phase composition of the obtained alloy includes mainly phases of titanium carbide and α-Fe. In the case of using the initial mixture with the Ni in the composition of the alloy along with the titanium carbide solid solution of Ni in alpha-iron and Ni-based compounds were identified. When Ni is used instead of Fe in initial powder mixture it leads to a noticeable refinement of the alloy grain structure: the size of the carbide grains is generally not more than 5-7 microns. With the decrease in Ni content in the mixture and respectively increase of iron content at the same Ti and graphite content, the particle size increases markedly and approaches with 5 % of Ni to the particle size of the alloy obtained from the mixture containing no Ni.