No 3 (2018)

The paper considers the problem of synthesis of nanocomposites based on the aluminum matrices reinforced with carbon nanotubes with the high physico-mechanical properties, as related to the achievement of a homogeneous dispersion of carbon nanotubes in the aluminum matrix of a composite. The authors developed the principles of the technology of preparation and determined the requirements for the parameters of the so-called normalized charge (a highly homogeneous dry mixture “aluminum powder - single-wall carbon nanotubes”) intended for the efficient synthesis of composite granules by the mechanical alloying.
Aluminum primary dispersed powder PAD-1 and the single-wall carbon nanotubes TUBALL were used as the raw materials, and the stearic acid was used as a process control agent. The processes of normalization and mechanical alloying were carried out in the mechanical reactor of the author's design. The derived composite pellets were exposed to cold and then to hot compaction. The paper shows the effectiveness of the new approach proposed by the authors to the implementation of effective reinforcement of the aluminum matrix powder by the nanotubes. This approach is based on the provision of effective dispersion of carbon nanotubes into alloyed matrix material by introducing the special technological operation -“normalization” of charge - in the technology of synthesis of composite granules, which are the semi-finished material for the production of a composite material with the high physical and technical characteristics.
The paper presents data on the strength parameters of the semi-finished aluminum matrix composites, which were produced using a normalized charge. It is shown that the application of the developed technology for charge normalization provides the increase in the strength characteristics of semi-finished composite materials by at least 25 % compared with the technologies without the application of normalization. The results obtained during the research can be used when improving the technologies of production of the aluminum matrix composites.

The depletion of the existing and the introduction of new oil fields lead to the continuously growing corrosion activity of the produced fluids what increases the intensity of breakdown of the oil field equipment. To ensure the adequate working capacity, it is necessary to develop and apply new steels with the increased strength and corrosion resistance. It is necessary as well to increase the volume and to develop new methods of field tests; based on such tests only it is possible to obtain the reliable understanding of the mechanisms and the kinetics of the ongoing processes of the corrosive-mechanical destruction and to assess the working capacity of the pipeline systems under the actual operating conditions of a certain field.
The authors present the developed techniques of three main types of pilot tests: the bypass lines, the intermittent monitoring of production strings and the intermittent monitoring of the operating pipelines. The characteristic feature of the suggested tests is the systematic comparative analysis of the current state with the states before operating and the states of preceding stages of tests. For this reason, pilot tests come with the additional tests that are combined in two groups according to their functionality. The first group characterizes the initial state of metal and the change of its properties after tests (chemical and phase composition, the structural condition of metal, mechanical properties, corrosion resistance). The second group characterizes the corrosion damage of the pipeline inner surface caused by the tests (the inner surface condition; the identification of the prevailing type of the corrosive destruction; the evaluation of the rate of general and local corrosion; phase and chemical composition and the morphology of corrosion products; microbiology testing).
The suggested testing techniques allow obtaining the fullest information on the operating capacity and the kinetics of pipes failure development under the certain operating conditions. As an example, the authors describe the results of comparative field tests of the TBG production strings made of 15H5MFBCh steel and of 35G2S and 35G2F conventional steels when operating on five fields with different composition of produced fluids.

Since the cause of the delayed destruction of the two-phase brasses is not fully determined, the commercial supplies of semi-finished products have unstable technological properties. As the result of experimental work, the author obtained the contradictory data on the root cause of cracking and the influence of grain growth during heating on the crack formation tendency. Meanwhile, the current requirements to the technological processes need the maximum loss minimization during the mill products processing.
The paper covers the issue of the selection of temperature intervals of hot plastic deformation to eliminate and determine the relationship between the β-phase grain size and the cracking carried out on the basis of industrial experiment followed by the comparative metallographic analysis of batches with different handling properties. For this purpose, the author carried out the comparative industrial experiment between the batches with different handling properties, determined the actual temperature of hot deformation, and performed the controlled forging at different heating temperatures. The subsequent metallographic analysis proved the assumption that the increase in the forging temperature can increase the level of deviations in some cases and reduce in the others. The author studied the influence of the initial microstructure of the CuMnAlFeNi 59-3.5-2.5-0.5-0.4 alloy, the heating temperature of forging by the level and the type of defects of work material for the blocking synchronizer rings made of different batches of tubes. It is determined that the conditions for the production of pipes are the more significant factor for cracking than the heating temperature at the certain interval. When heating up to 780 °C, the large grains are formed in the individual batches that may be caused by the initial β'-phase grain texture but is not the root cause of destruction. When heating up to 700 °C, the high dispersion silicides do not dissolve, what may cause the origination of hidden cracks during forging. The optimum heating temperature is 750 °C.

The temperature of a cutting process influences significantly the quality of the treated surface and the performance of a tool. The rational use of vibrations, including the ultrasonic frequency vibrations is one of the means to improve the efficiency of a cutting process. However, there are no analytical studies of the temperature of turning with vibration superposition. It was accepted that the total heat output power when turning was equal to the sum of heat output powers of sources aroused as the result of the transition to the heat of work of deformation and work of friction forces on the leading and flank surfaces of a tool. The paper presents the mathematical dependences for calculation of the components of the total power of heat release. The authors took into account that the yield stress, which determines the cutting and frictional forces on the contact surfaces of a cutter, workpiece, and chip, depends on the temperature in the plastic deformation area. The law of distribution of thermal power density on the shear plane was taken as uniform; the combined law was adopted on the surface of the contact of a chip with the front surface of a cutter; the asymmetric normal law was adopted on the surface of the contact of a cutter with a workpiece. The authors gave the dependence for the calculation of the cutting depth when applying vibrations in the direction perpendicular to the treated surface. Heat exchange at the boundaries of the objects contacting with the process liquid or air is given in the form of the Newton-Richman law. The thermal conductivity equations of the contacting objects were solved in combination with the general boundary conditions in the contact zone using the finite element method. The method of calculation based on the discrete analogs of the heat conduction equations is implemented in the original programs. The authors compared the results of calculation of temperatures when turning without the vibrations superposition with the experimentally obtained results, in this case, the discrepancy between the calculated and experimental values does not exceed 10 %. The simulation of the turning process with the superposition of ultrasonic vibrations showed that the main component of the cutting force Pz reduced by a mean of 11 %, the maximum temperature in the zone of contact of the back surface of a cutter with a workpiece reduced by 20 %, and the maximum temperature in the zone of contact of the front surface of a cutter with a chip reduced by 26 %.