The effect of the additions of nanodispersed diamonds on physico-mechanical properties of the drilling tool metal matrix

The results of the studies of the effect of the ASUD99 grade nanodiamonds additions on physico-mechanical properties of the drilling tool metal matrix have been discussed. The optimal concentration of nanodiamond powder additives in the composition of a hard alloy mixture has been defined. The addition of 1–2 wt % nanodispersed diamonds has been shown to contribute to binding oxygen in the thermooxidation of diamond in the course of the tool manufacture, which makes it possible to reduce the amount of pores in the matrix material structure and to increase its density by 1.7% and hardness by 24.3%.     

Influence of various acids on the physico-mechanical properties of pozzolanic cement mortars

Acidic attack represents a topic of increasing significance, owing to the spread of damages of concrete structures in both urban and industrial areas. Cement type is an important factor affecting performance of cement based materials in an aggressive environment. The goal of this study was to compare the acid resistance of a pozzolanic cement (CEM IV-A/32·5) with Portland cement (CEM I 32·5) that was made from the same clinker. For this purpose, 50mm mortar cubes were prepared with two different kinds of cement according to TS EN 196-1. After 28 days of hardening, the samples were immersed into four different concentrations of hydrochloric, nitric and sulfuric acid solutions for a period of 120 days. The changes in weight loss and compressive strength values for each acid solution within the test period were recorded. The acid resistance of mortars made from Portland cement was better than the pozzolanic cement incorporated samples after 120 days of acid attack.     

Investigation of certain physico-mechanical properties of steel St. 45 borided by various methods under various conditions

The article reports the results of study of the effect of bonding (by various methods and under various conditions) on certain mechanical properties of steel St. 45 under static, impact and cyclic loads in air and in a corrosive medium.     

The electron energy dependence of the TL response for CVD diamonds

The thermoluminescent (TL) response of CVD diamond is investigated after bombarding a sample with monoenergetic electrons (at 6 and 21 MeV). Irradiations are performed at room temperature with a medical linear electron accelerator PRIMUS (KD2-Siemens). The TL curve shows a peak at approximately 540 K. The area of this peak as a function of fluence exhibits saturation behaviour at high energies. Moreover, there is no significant difference between the TL response at 21 MeV electrons and that at 6 MeV. In order to explain these experimental results, calculations of the ionising dose have been performed with the code MCNPX (Monte Carlo N-Particle) for various incident energies from 0.1 MeV up to 100 MeV.     

含硼金刚石与普通金刚石半导体性及抗氧化性比较

通过在铁基合金中加入硼粉的方法,制成含硼量0.2%(质量分数)的Fe-Ni-C-B系触媒,用静压法合成含硼金刚石.研究了普通金刚石和含硼金刚石的形貌、晶体结构、电阻-温度曲线和抗氧化性.实验表明,合成的含硼金刚石具有良好的半导体性,电离能ΔE=0.368eV;起始氧化温度比普通金刚石高185℃,耐热性明显改善.此方法为低成本、大批量的制备半导体金刚石提供了新的途径.     

Structure and properties of impact diamonds from the Popigai Deposit and polycrystals based on them

Properties of impact diamonds from the Popigai Deposit have been studied in a free state and in a composition of a compact. Raman spectra have been taken of the initial micron powders and polycrystals HP-HT sintered both in the presence of sintering aids and without them. Hardness, H _V , of sintered polycrystals have been found, structural variations in diamond crystal lattice depending on the sintering conditions have been studied.     

Mechanical properties of polycrystalline diamonds

Abstract

The room temperature mechanical properties of polycrystalline diamonds, i.e. tensile strength, transverse rupture strength, compressive strength, impact strength, fracture toughness, and elastic constants, have been determined. The applied test techniques are described and the results compared with those obtained by other authors. The fracture mode under the present experimental conditions was primarily transgranular. A grain size dependence, where strength increases with decreasing grain size, has been found. Fracture toughness was found to go through a maximum for grain sizes between 10 to 30 μm. The modulus of elasticity increases with increasing grain size. An influence of cobalt content on strength and modulus of elasticity has been found, while no significant influence on toughness could be determined. Increasing the cobalt content increases strength, but has the inverse effect on the modulus of elasticity. The results of strength, toughness, and elastic constants measurements are discussed in terms of available models and theories of polycrystalline ceramic materials. It can be seen from the results that polycrystalline diamonds behave in a manner similar to that of most engineering ceramics, but have the distinct advantage of a higher fracture toughness.

MST/596     

Comparative physico-mechanical characteristics of micron powders of synthetic and natural diamonds and polycrystalline composite materials based on them

Physico-mechanical characteristics of micron powders of synthetic (SD 40/28) and natural (ND 40/28) diamonds and of polycrystalline composite materials based on them have been studied. Both the powders have been shown to meet the requirements of DSTU 3292-95 (State Standard of Ukraine). At the same time the abrasiveness of natural diamond is higher than that of synthetic diamond, while the grain density and specific surface is lower than that of synthetic diamond grains. The elastic characteristics of sintered polycrystalline composite materials (the Young modulus, shear modulus, bulk modulus, Poisson ratio, and wear resistance in stone working by friction) of a composite sintered from the natural diamond micron powder are higher, while the life at cyclic compression is somewhat lower as compared to a composite sintered from the synthetic diamond micron powder.     

Structure and properties of Si-Ti-C-O fibre-bonded ceramic material

Si-Ti-C-O fibre-bonded ceramic material was synthesized from pre-oxidized Si-Ti-C-O fibre with an oxide layer 400–600 nm thick, by hot-pressing at 2023 K under 50–70 MPa. The interstices in the Si-Ti-C-O fibre-bonded ceramic material were packed with an oxide material which existed on the surface of the pre-oxidized Si-Ti-C-O fibre, and the oxide material formed a small amount of the matrix phase (10 vol%). At the fibre-matrix interface, aligned turbostratic carbon, which was oriented around the fibre, was formed during hot-pressing. The existence of the interfacial carbon layer indicated the Si-Ti-C-O fibre-bonded ceramic material to have a fibrous fracture pattern with high fracture energy. The Si-Ti-C-O fibre-bonded ceramic material showed excellent durability even at 1773 K in air, because a protective oxide layer is formed on the surface at a high temperature (above 1273 K) in air. Moreover, the Si-Ti-C-O fibre-bonded ceramic material almost maintained its initial strength in the bending and tensile tests, even at 1773 K in air.     

Influence of ion implantation and overlay coatings on various physico-mechanical and wear properties of stainless steel,titanium and aluminium

This work represents the data on the wear behaviour of 304 stainless steel, commercial grade titanium and commercial grade aluminium without and with different surface treatments, namely ion implantation of boron and nitrogen and overlay coatings of titanium carbide and nitride.The surface treatments were characterized by phase identification, hardness, bend strength, as well as adhesion of overlay coatings. Wear properties were evaluated in adhesive, erosive and abrasive modes of wear.The experimental results showed that surface treatments produced measurable changes in hardness and strength. The results of adhesive wear tests indicated that the wear resistance of all the substrate materials can be considerably improved by overlay coating with superhard materials in dry as well as lubricated test conditions. Ion implantation resulted in improvement of wear properties for only a limited regime of adhesive wear under lubricated conditions and for the abrasive mode of wear. Overlay coatings produced a marked improvement in abrasive wear tests under lubricated conditions on all substrate materials.     

Structure and optical properties of vacuum-deposited scandium films on crystalline substrates

Thin films of scandium have been deposited in high vacuum on to amorphous and crystalline substrates at room temperature. These films were examined by X-ray diffraction and transmission electron microscopy to study the structure and orientation of films of various thicknesses. It was observed that thin scandium films evaporated on to air-cleaved mica and rocksalt substrates have a polycrystalline structure. The variation of the refractive indexn, the extinction coefficientk and optical conductivity ₁ () with wavelength were studied. Measurements were made in the spectral region from 2.5 to 40m.     

Structure and properties of melt-spun iron-silicon alloy filaments having single crystalline structure

Melt-spun iron-silicon (Fe-Si) alloy filaments were obtained by a rapid solidification method using an in-rotating-water spinning apparatus. The silicon content in the alloy composition was selected to be about 6.5% by weight, which is expected to have no magnetostriction and to show the lowest coercive force in the magnetic field. Heat-treated filaments were also investigated in terms of the structure and the mechanical and magnetic properties. It was found that the cross-sectional areas and structures of as-spun filaments were affected by processing conditions, such as spinneret diameter, throughput, etc. In the case of the filaments with diameters less than about 90 m, well-grown structures having primary dendrite arms oriented towards the direction of the filament length, can be observed in place of the polycrystalline structure. By means of high-temperature heat treatment, the filaments with the above structure were found to show single-crystalline structure without any clear boundary. The single-crystalline filaments were found to have good ductility to bending through 180 ° and excellent magnetic properties such as an almost perfect rectangular loop, low coercive force, and high saturation magnetic flux density in the d.c. magnetization curve.     

Structure and mechanical properties of the extruded blends of a liquid crystalline polymer with polypropylene

Blends of a thermoplastic, isotatic polypropylene (PP) and a liquid-crystalline polymer (LCP) based on a copolyester of hydroxynapthoic acid and hydroxybenzoic acid, were extruded. The LCP exhibited a higher viscosity than that of the PP under the extrusion conditions. Calorimetric, microscopic, static and dynamic mechanical tests were performed on these blends. Differential scanning calorimetry thermograms indicated that the crystallization temperature of PP increases slightly with increasing LCP content. Scanning electron microscopy examinations revealed that the LCP phase was elongated into microfibrils in the blends investigated. However, some undeformed spherical droplets were dispersed in the PP matrix in addition to microfibrils for the blends containing high LCP concentrations. Static tensile tests showed that the addition of LCP to PP results in an increase of the modulus of elasticity but a decrease in tensile strength. The storage modulus of the extruded blends was found to increase with the addition of LCP.     

Effect of boriding on some physico-mechanical properties of steel 45

The effect of diffusion bonding (in relation to the subsequent heat treatment) on the static and fatigue strength of steel 45 in air and corrosive media was studied.     

Structure and electrical properties of crystalline and glassy Ag2PbP2O7

Single crystals of Ag₂PbP₂O₇ have been prepared by melting of the crystalline phase under phosphate flux. Ag₂PbP₂O₇, isotype of Na₂PbP₂O₇, is of triclinic symmetry with the space group P(−1) (Z=2). The unit cell parameters are: a=5.502(6) Å, b=7.008(8) Å, c=10.018(9) Å, α=106.63(6)°, β=93.89(7)°, γ=110,68(6)°. The lattice of Ag₂PbP₂O₇ consists of corner-shared structural units {Pb₂P₄O₁₄}⁴⁻, which form ribbons parallel to the [010] direction. The {Pb₂P₄O₁₄}⁴⁻ units result from the association of corner-shared PbO₅ polyhedra and P₂O₇ pyrophosphate groups. The ribbons are interconnected by Pb–O–P bridges in the [100] direction and form lamina parallel to (001) plan. Silver atoms are located between two alternating lamina. Glasses with the same composition as the crystalline phase have been synthesized. A study of transport properties of Ag₂PbP₂O₇ in the crystalline and glassy forms is reported.     

Aluminum doped silicon carbide thin films prepared by hot-wire CVD: Influence of the substrate temperature on material properties

Successful p-type doping of μc-SiC:H with Al introduced from trimethylaluminum has been already demonstrated. In this work we focus on the influence of substrate temperature (T_S = 300-390 °C) on the Al-doping. As T_S is reduced from 390 °C to 300 °C, the crystallinity decreases from 75% to 55% and the dark conductivity σ_D decreases first by about three orders of magnitude before increasing again at T_S = 300 °C. Both microstructure, as determined from Raman spectroscopy, and optical absorption are little affected by the change in T_S. Upon annealing at 450 °C in vacuum, σ_D increases typically by two orders of magnitude up to 10⁻⁴ S/cm, which is explained by dopant activation as a result of hydrogen desorption. It is concluded that a process temperature > 350 °C is needed to obtain effective Al-doping for p-type μc-SiC:H thin films.     

Superconducting properties of CVD tantalum films

Tantalum films on A1₂O₃ substrate are obtained by CVD of TaCl₅ at atmospheric pressure. The critical temperature of the transition to the superconducting state, the critical magnetic field and the volt-ampère characteristics of the films are investigated. Significant increase in the critical magnetic field and the typical behaviour of type II superconductors was established.     

GaN nanowires: CVD synthesis and properties

The growth of GaN nanowires from Ga and NH₃ sources in the flow of Ar carrier gas using a chemical vapor deposition (CVD) system was systematically studied. The substrates used were Si(111) and Si(100). Fabricated nanowires were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). We investigated the influence of growth temperature, catalyst used, Ga amount, and the ratio of Ar and NH₃ flow rates on the morphology and properties of GaN nanowires. We found that the best results were obtained for a growth temperature of 950 °C. Optimal catalysts were Au and metallic Ni, while the use of nickel nitrate was found to lead to formation of SiO_x nanowire bunches in addition to GaN nanowires. For the optimal temperature and catalyst used, the influence of the Ga to N ratio on the nanowire growth was studied. It was found that different types of nanostructures are observed in relatively Ga-rich and in relatively N-rich conditions. Growth mechanisms of different types of nanowires, including the stacked-cone nanowires and the microscale structures formed by lateral growth under N-rich conditions, are discussed.     

Structure and mechanical properties of corn kernels: a hybrid composite material

The mechanical properties of corn kernels were evaluated at three levels of kernel structure, varying in the proportions of horny endosperm, and six levels of moisture content in the range of 6 to 34% (wet basis) under a compression mode of loading. The observed values of ultimate stress, modulus of elasticity, modulus of toughness and modulus of resilience varied from 8 to 82 MPa, 20 to 480 MPa, 0.8 to 4.4 MJ m^–3 and 0.2 to 0.8 MJ m^–3, respectively, within the experimental range. Each of these properties decreased in magnitude as the moisture content increased. The microscopic study revealed that the resistance of kernels to fracture was predominantly influenced by the kernel structure. The size of cracks increased with increasing strain or decreasing proportion of the horny endosperm in the kernels. The viscoelastic behaviour of the kernels was determined at two levels of kernel structure, five levels of kernel moisture (12 to 34%) with three deformation rates (1.27, 5.08 and 12.7 mm min^–1) by means of stress relaxation tests. The analysis of the test data suggested that the hybrid composite kernels were hydrorheologically simple materials.