No 4 (2016)
TECHNOLOGY
Development of hardware and software for the control of internal defects and residual resource of engineered structures and parts made of fiberglass
Abstract
The identification of defects in advanced composite materials by the means of ultrasonic signal is considered and analysis of the residual resource of engineered structures is made. The main defects in the structure of composite materials are the following: displacement, rotation and warping of the individual layers of the reinforcing material; superficial swelling, separation, distortion; increased porosity, cracks, sinks, uneven shrinkage materials; reduction in adhesion of the binder and filler, and others. The early recognition of defects and forecasting of the residual resource of engineered structures gives the opportunity to avoid the loss of sealing of engineered parts and structures, environmental problems concerned with the destruction of pipelines. Undetected internal defects can not only lead to significant economic losses, environmental pollution, but also to the loss of human life. The working conditions of the plastic materials, especially composites, are widely used for replacement of parts and components made of rare materials, ferrous and nonferrous metals and alloys based on them, working in hostile environments. This makes it possible to improve the reliability and durability of the structure as a whole. However, in modern working conditions to evaluate the quality of products a lot of enterprises have to selectively destroy the integrity of the samples under investigation in the control of material properties. From an economic point of view, this leads to an increase of the production cycle and the cost of production. A method of ultrasonic diagnostics using hardware-software complex, allowing to reveal internal defects, the presence of inclusions or inhomogeneities on the structure of the composite material without destroying the product, to reduce the economic, environmental and human costs is offered.
Obrabotka Metallov / Metal Working and Material Science. 2016;(4):6-15
6-15
EQUIPMENT. INSTRUMENTS
About a destruction of diamond grains in the grinding process
Abstract
An analysis of modern trends in the area of metal processing shows that at the moment the diamond tool is at the peak of its popularity. It can be confirmed by the fact that the diamond tools are stay ahead in the number of search queries on the Internet. It leaves behind tool made of cubic boron nitride, silicon carbide and green silicon carbide. Moreover, there is a tendency on the steady increase of interest to the diamond grinding wheel in the metal processing industry and mechanical engineering complex. This popularity is due to the fact that manufacturing based on the latest research learned how to effectively use the tools of synthetic diamond. However, experience shows that almost every diamond has various defects that have a characteristic influence on its destruction and deterioration that should be considered in the operation of devices and products containing diamonds. Defects occur in diamond crystals during its synthesis, give rise to the formation of more complex defects that occur in the operational process of diamonds. Under external influence these defects have immediate strong effect on production characteristics of devices, products or instruments containing diamonds. The analysis of the scanning electron microscopy images shows that even on the surface of the diamond grains and on their edges that are not involved in the process of cutting, there are typical traces of lattice disturbance both on micro and macro levels. This indicates that disturbance of the diamond grains usually happens due to bulk defects, which have a length of several nanometers to micrometers, and represent blocks of the crystal lattice, between which cracks and cracks are usually filled with metallic inclusions. A visualization method, developed on the basis of modern digital technology and molecular dynamics, shows it for atomic-scale.
Obrabotka Metallov / Metal Working and Material Science. 2016;(4):16-23
16-23
Determination of the rigidity and deformation energy of the technological machine load-carrying systems
Abstract
Problems of determining deformation energy in load-carrying systems of technological machines and energetic relations between them during technological operations are discussed. The goal of this study is to develop recommendations for modernization of the construction of load-carrying systems using the STB loom for production of dense fabrics as an example. The analysis of scientific literature on this problem indicates that sufficient attention is not devoted to the effect of load-carrying system elements on the loom feeding system. This study is urgent due to the lack of a general approach making it possible to set the parameters of load-carrying systems with the account of technological requirements and quality of obtained product. To determine deformation energy, a computational model of a loom for production of dense fabrics including a stationary tension bar and a tension tube as a support for warp threads is examined. The deformation energies of the load-carrying and tension systems of STB-180 loom and movements of construction elements depending on the technological force varied in the range of 4000-10000 N is determined using SolidWorks CAD system and finite-element CAE complex ANSYS. The analysis of the calculation results indicates that the deformation energy of the load-carrying system and tension tubes is about 25% of the effective energy used for the fabric production. This fact indicates that it is necessary to improve the rigidity of the load-carrying and tension systems. An improved construction of the loom of production of dense fabrics is suggested based on the results of the studies. This model includes additional supports for the stationary tension bar and tension tube basing on the front tie. The analysis of the calculation results with the account of the suggested improvement of construction elements showed that the deformation energy for the modernized loom has been significantly reduced. The obtained results allowed us to suggest specific recommendations for improvement of the constructions of the load-carrying and tension systems in STB looms for production of dense and technical fabrics.
Obrabotka Metallov / Metal Working and Material Science. 2016;(4):24-33
24-33
MATERIAL SCIENCE
Investigation of the structure of Ti-40Nb powder alloy obtained by mechanical activation
Abstract
Powder alloys obtained by mechanical activation are widely used in different fields. One of these fields is additive technology. The resulting material for such purpose should have a size distribution of 10…50 µm, nearly spherical particles shape and phase composition close to the composition of the alloy obtained by melting. The powder Ti-Nb alloy is consisted of Ti and Nb powders mixture with weight ratio of 60:40 respectively, grinded in a planetary ball mill AGO-2C in argon atmosphere. The structure and phase composition of obtained powder alloy are defined by mechanical activation time and the presence of protective gas environment. The size of formed particles increases up to average value of 66 µm at activation time increasing from 3 to 20 minutes and it decreases twice at activation time of 25 minutes. The shape of particles changes from scaly to pellet. The quantity of total solid solution of Ti and Nb components increases in the alloy with increasing the activation time. The β-single phase alloy is identified by x-ray at activation time of 20 minutes. Plastic deformation is accompanied by relaxation processes of diffusion type and occurs during mechanical activation. The process of agglomeration begins to predominate over the process of destruction. As a result, the average size of resulting powder particles increases with increasing the treatment time and sticking of powder material to the vial walls is observed. The balancing of agglomeration and destruction process occurs at activation time of 25 minutes. This leads to the average size of obtained particles decreasing. Significant increment of accumulated strain energy creates conditions for abnormal mass transfer of components atoms into the crystal lattice of each other. Also it creates conditions for the formation of monophase alloy, which consists of a total solid solution of β-TiNb. This solid solution exists in a range of concentrations. It is necessary to investigate ratio of technological parameters of mechanical activation, granulometric and phase composition of resulting powder in case when investigated powder is used in the process of selective laser melting.
Obrabotka Metallov / Metal Working and Material Science. 2016;(4):34-42
34-42
The morphology of the carbides in high-carbon alloys such as damascus steel
Abstract
Analysis of changes in the morphology of carbides of the unalloyed high-carbon alloys such as damascus steel depending on the degree of supercooling of the melt, treatment and plastic deformation is conducted. It is shown that the crystallization process of the alloy with high carbon content (2.25 % C) at high degrees of supercooling is characterized by features typical for high-carbon steel. It is shown that the hot deformation of damascus steel with the structure of Widmannstätten cementite does not lead to its crushing. Plates of Widmannstätten cementite split into separate layers with a thickness 0.6…1.0 μm. However, the formation of such materials’ structure does not provide good cutting properties of the tool. Formation of ledeburite structure which is similar to ledeburite of white cast iron is found after high temperature annealing of the initial structure at 1150 °C for 2 hours. Two competing processes of forming proeutectoid carbides at strain of damascus steel, associated with spherodization and particles faceting, are determined. Three alternatives of the formation of eutectic carbides with faceted prismatic shape in iron-carbon alloys are considered. One of them involves thermal division of plates of secondary cementite or ledeburite cementite into separate microvolumes. The second alternative involves crushing of cementite crystals during deformation of the material and the formation of angular fragments. The third option is based on the conversion of metastable ledeburite cementite into stable carbides having prismatic morphology. It is shown that carbide heterogeneity in the unalloyed high-carbon steels such as damaskus is an aggregate of large faceted eutectic carbides with prismatic shape. It is expected that the formation of proeutectoid cementite with faceted prismatic form will have positive effect on the properties of cutting tool.
Obrabotka Metallov / Metal Working and Material Science. 2016;(4):43-51
43-51
The influence of flowing temperature on the structure and properties of the self-fluxing coatings
Abstract
The coatings made of self-fluxing powder of the Ni-Cr-Si-B system (Ni - base; 15.1 wt. % Сr; 2.0 wt. % Si; 2.0 wt. % В; 0.4 wt. % С) are deposited on low carbon steel substrate (0.2 wt. % C) by plasma spraying. The study considers the influence of flowing temperature on structure and properties of the specified materials. The samples with coatings are heated in furnace up to 1030, 1050, 1070 and 1100 ºС for 1 hour with the following air cooling. The structure and phase composition of the coatings is investigated using optical and scanning electron microscopy, and X-ray diffractometry. Moreover, the results of microhardness measuring and wear-resistance testing in conditions of sliding friction are demonstrated. X-ray diffractometry showed that the major phases of the coatings before fluxing and after one are the following: γ-Ni, Ni3B, CrB и Сr7С3. The results obtained using optical and scanning electron microscopy brought out that the coatings fluxed at 1030, 1050 and 1070 ºС consist of dendrites of solid solution of Cr, Si and Fe in γ-Ni, Cr7C3, CrB inclusions and Ni-Ni3B, Ni3B-Ni6Si2B eutectics. The coatings fluxed at 1100 ºС consist of dendrites of solid solution of Cr, Si and Fe in γ-Ni, Cr7C3, CrB2 inclusions and (γ-Ni)-CrB, Ni-Ni3B eutectics. A quantity of hard phases (eutectic, chromium carbides and chromium borides) increases with the rise of temperature. It leads to increase of microhardness and wear-resistance of the coatings. The results of the experiments demonstrate that the coatings fluxed at 1100 ºС have maximum microhardness (953 HV) and wear resistance. Unfortunately, high fluxing temperatures can promote to layer separation.
Obrabotka Metallov / Metal Working and Material Science. 2016;(4):52-62
52-62
Structure and properties of TiB-TiC-Ti layers fabricated on CP-titanium substrates by electron beam cladding
Abstract
The influence of non-vacuum electron beam treatment modes on the structure and properties of wear resistant TiB-TiC-Ti layers formed on the surface of VT1-0 titanium alloy is investigated. A mixture of titanium, boron carbide and flux powders is used as filler. The structure and phase composition of the layers are investigated by the means of optical microscopy and scanning electron microscopy, and X-ray diffractometry. The experiments resulted in the formation of layers with the thickness of 3.4 mm consisting of α (α´)-Ti, titanium carbide and titanium monoboride. Structural investigations revealed a high volume fraction of TiC and TiB reinforcing compounds contributed in the formation of cracks in the cladded layers. Variation of technological regimes of the electron beam treatment affected the hardness of cladded layers. Treatment of the sample containing 20 wt. % of boron carbide in a filler with a beam current of 22 µA led to the formation of the layer with hardness of 582 HV. This value was about 3.5-fold higher than titanium microhardness. Increase of a beam current by 1 µA resulted in decrease of the microhardness level to 543 HV. Treatment of the sample containing 12 wt. % of boron carbide in a filler led to the formation of the layer with hardness of 436 HV. Wear resistance of fabricated materials is estimated in the conditions of friction by non-rigidly fixed abrasive particles. The best characteristics possessed the layers obtained by cladding of 20 wt. % boron carbide. Intensity of wear of the coated samples was 8-fold lower comparing to CP-titanium.
Obrabotka Metallov / Metal Working and Material Science. 2016;(4):63-74
63-74