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13COMPARISON OF THE INFLUENCE OF VIBRATION AND CENTRIFUGAL FORCES FOR THE FORMATION OF HARD ALLOYS
G. Zakharov*", Z. Aslamazashvili", G. Tavadze", G. Oniashvili", T. Batsikadze",
and D. Kvaskhvadze"
aF. Tavadze Metallurgy and Materials Science Institute, Tbilisi, 0186 Georgia
*e-mail: algar@mail.ru
DOI: 10.24411/9999-0014A-2019-10199
During self-propagating high-temperature synthesis (SHS) external influences, such as pressure, ultrasound, centrifugal force, etc. have significant effect on structure and physical and mechanical characteristics when forming a target product [1-5]. These can be achieved by applying SHS-compaction and SHS-metallurgy [6, 7]. In SHS processes at the minimum "critical" sizes of a reactionary form (internal diameter and length) synthesis of exothermic chasm does not proceed that is the well-known fact. The minimum critical internal diameter of a reactionary form to be in repartitions is 8-12mm, which depends on structure, density, and methods of impact on exothermic mixture during synthesis of target material. These technological disadvantages can be overcome by the SHS-extrusion method. One of the most important process parameters of SHS extrusion is delay-time pressing. At small delay time expression is practically not observed, material does not succeed to be synthesized completely. At large time delay material loses the plastic properties and there is an obstruction of a matrix. It should be noted that an optimum interval of time delay is very narrow and defined as 4.5-6.5 s [8]. Search for new technology solutions for synthesis of materials and receiving samples with a critical internal diameter of a reactionary form is a topical task.
For comparison of quality of the received cast solid alloy experiments were conducted in the high-pressure reactor and in the laboratory centrifugal machine.
Samples were obtained from the solid alloy developed after studing multicomponent system: NiO-Cr2O3-Co3O4-WO3-TiO2-MoO3-B2O3-Nb-Zr-C -Al.
By using the laboratory centrifugal machine the prepared exothermic mixture was placed in a graphite glass in which placed a graphite form-building element with an internal diameter of 18 mm and with the height of sample of 45 mm. The limitation of height of a sample was connected to design of the centrifugal machine which did not allow receiving a sample more than 45 mm in length. At the established rotation speed of 2000 rpm the exothermic mixture/chasm was initiated. Figure 1 shows samples of various geometrical form with height of 45 mm which are dense and pore-free.
Fig. 1. The cast samples with various geometrical form with height of 45 mm received by laboratory centrifugal machine.
XV International Symposium on Self-Propagating High-Temperature Synthesis
In the high pressure reactor samples with diameter ~ D = 15 mm and 110 mm in length were obtained. Researches were directed to receiving dense material from solid alloy by vibrations and with the changing frequency and amplitude. Frequency of vibrations was ranging from 50 up to 100 Hz, amplitudes was 0.1 and 0.2 mm. For experiments the vibration device shown in Fig. 2 (general view (a) and the drawing in 3D format (b)) was designed. Necessary frequency of vibrations was carried out by means of the developed electronic device (Frequency Generator), the scheme is presented in Fig. 3.
(a) (b)
Fig. 2. Vibration installation: interior (a), drawing in 3D (b). 1 graphite adapter, 2 quartz forming tube, 3 graphite form, 4 protective glass, 5 vibrating table.
Fig. 3. Principal scheme of electronic installation (Frequency Generator).
Chasm components are preliminary dried, dosed and mixed. Chasm in weight of 250 g was loaded into a graphite form of the vibration device which was then placed in a high-pressure reactor. The initiating spiral was fixed on conductor cables, and brought into contact with exothermic chasm. It must be note that the scheme was assembled so that the mechanism of the vibration device starts just after the initiation of exothermic mixture and burning of an electric spiral. The general scheme of the vibration device placed in high pressure reactor and connection of electronic device is presented in Fig. 4.
Fig 4. Scheme of the vibration installation placed in high pressure reactor 1 graphite form, 2 chasm, 3 mechanism of vertical shift of a vibration table from 0.1 to 0.2 mm providing the required amplitudes of fluctuations of the formed sample, 4 vibration table, 5 clamp, 6 transformator, 7 shock rod, 8 initiating spiral, 9 conductor cables, 10 internal contour of high pressure reactor, 11 frequency generator.
Experiments were made in the atmosphere of nitrogen under a pressure of 30 atm. The received samples are presented in Fig. 5.
Fig. 5. The samples received in the high-pressure reactor as a result of vibration:
1 amplitude of fluctuations is 0.1 mm, frequency is 50 Hz;
2 amplitude of fluctuations is 0.2 mm, frequency is 100 Hz;
3 amplitude of fluctuations is 0.2 mm, frequency is 50 Hz;
4 amplitude of fluctuations is 0.1 mm, frequency is 100 Hz.
It is visible that with increase in frequency and amplitude of fluctuations the porosity of material is considerably reduced.
The analysis of the received results showed that synthesis of materials with a critical internal diameter and length with more than 45 mm can be realized by increasing the length of the reactionary camera of the centrifugal machine. For realization of the task, it is planned to be developed (modernization) of the laboratory centrifugal machine. Realization of a task of receiving pore-free materials in high pressure reactor demands to improve a design and the electronic system of the vibration device.
On the basis of the received experimental results was outlined tendency for obtaining the optimistic final results. For the solution of set tasks research works will be continued. The result will be achieved after development of new devices. It will allow to synthesize materials and products with a critical internal diameter of a reactionary form and not less than 110 mm in length under conditions of centrifugal force and in high pressure reactor.
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