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Dina V. Dudina,Vyacheslav I. Mali,Alexander G. Anisimov,Natalia V. Bulina,Michail A. Korchagin,Oleg I. Lomovsky,Ivan A. Bataev,Vladimir A. Bataev 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.6
We present several possible microstructure development scenarios in Ti3SiC2-Cu composites during mechanical milling and Spark Plasma Sintering (SPS). We have studied the effect of in situ consolidation during milling of Ti3SiC2 and Cu powders and melting of the Cu matrix during the SPS on the hardness and electrical conductivity of the sintered materials. Under low-energy milling, (3-5) vol.%Ti3SiC2-Cu composite particles of platelet morphology formed, which could be easily SPS-ed to 92-95% relative density. Under high-energy milling, millimeter-scale (3-5) vol.%Ti3SiC2-Cu granules formed as a result of in situ consolidation and presented a challenge to be sintered into a bulk fully dense sample; the corresponding SPS-ed compacts demonstrated a finer-grained Cu matrix and more significant levels of hardening compared to composites of the same composition processed by low-energy milling. The 3 vol.% Ti3SiC2-Cu in situ consolidated and Spark Plasma Sintered granules showed an extremely high hardness of 227 HV. High electrical conductivity of the Ti3SiC2-Cu composites sintered from the granules was an indication of efficient sintering of the granules to each other. Partial melting of the Cu matrix, if induced during the SPS, compromised the phase stability and uniformity of the microstructure of the Ti3SiC2-Cu composites and thus it is not to be suggested as a pathway to enhanced densification in this system.
A tandem GI/PH/1→*/PH/1/0 queue with blocking
Klimenok, V.,Kim, C.,Dudina, O.,Dudin, A. Elsevier Science Ltd 2013 Applied mathematical modelling Vol.37 No.10
Tandem queues are widely used in mathematical modeling of random processes describing the operation of manufacturing systems, supply chains, computer and telecommunication networks. Although there exists a lot of publications on tandem queueing systems, analytical research on tandem queues with non-Markovian input is very limited. In this paper, the results of analytical investigation of two-node tandem queue with arbitrary distribution of inter-arrival times are presented. The first station of the tandem is represented by a single-server queue with infinite waiting room. After service at the first station, a customer proceeds to the second station that is described by a single-server queue without a buffer. Service times of a customer at the first and the second server have PH (Phase-type) distributions. A customer, who completes service at the first server and meets a busy second server, is forced to wait at the first server until the second server becomes available. During the waiting period, the first server becomes blocked, i.e., not available for service of customers. We calculate the joint stationary distribution of the system states at the embedded epochs and at arbitrary time. The Laplace-Stieltjes transform of the sojourn time distribution is derived. Key performance measures are calculated and numerical results presented.
TiB<sub>2</sub>-Cu Interpenetrating Phase Composites Produced by Spark-plasma Sintering
Kwon, Young-Soon,V. Dudina, Dina,I. Lomovsky, Oleg,A. Korchagin, Michail,Kim, Ji-Soon The Korean Powder Metallurgy Institute 2003 한국분말재료학회지 (KPMI) Vol.10 No.3
Interpenetrating phase composites of $TiB_2$-Cu system were produced via Spark-Plasma Sintering (SPS) oi nanocomposite powders. Under simultaneous action of pressure, temperature and electric current titanium diboride nanoparticles distributed in copper matrix move, agglomerate and form a fine-grained skeleton. Increasing SPS-temperature and he]ding time promote densification due to local melting of copper matrix When copper melting is avoided the compacts contain 17-20% porosity but titanium diboride skeleton is still formed representing the feature of SPS . High degree of densification and formation of titanium diboride network result in increased hardness of high-temperature SPS-compacts.
Kim, Ji Soon,Dudina, Dina V,Kim, Jin Chun,Kwon, Young Soon,Park, Jin Ju,Rhee, Chang Kyu American Scientific Publishers 2010 Journal of Nanoscience and Nanotechnology Vol.10 No.1
<P>One of the possible reasons for low conductivity of in-situ produced dispersion strengthened copper matrix composites may be the incompleteness of the reaction between the initial reactants that remain in a state of solid solutions in the copper matrix. We report in-situ synthesis of TiB2-Cu composites starting from the powder mixtures with the limited content of copper ensuring a high probability of contact between the particles of titanium and boron and, as a result, their full conversion into the TiB2 phase. The nanoparticles were formed in a self-propagating mode in the ball milled Ti-B-Cu powder mixture corresponding to 57 vol.% TiB2-Cu composition. Afterwards, the system was 'diluted' with the required amount of the copper matrix using subsequent ball milling. Highly conductive 4.5 vol.% TiB2-Cu composites showing 82-87% IACS (International Annealed Copper Standard) conductivity were obtained by Spark Plasma Sintering (SPS) of the powders.</P>
Shock-wave Synthesis of Titanium Diboride in Copper Matrix and Compaction of -Cu Nanocomposites
Lomovsky O.I.,Mali V.I.,Dudina D.V.,Korchagin M.A.,Kwon D.H.,Kim J.S.,Kwon Y.S. 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
We studied formation of nanostructured -Cu composites under shock wave conditions. We investigated the influence of preliminary mechanical activation (MA) of Ti-B-Cu powder mixtures on the peculiarities of the reaction between Ti and B under shock wave. In the MA-ed mixture the reaction proceeded completely while in the non-activated mixture the reagents remained along with the product . titanium diboride. The size of titanium diboride particles in the central part of the compact was 100-300 nm.
In-situ Synthesis of Cu-TiB<sub>2</sub> Nanocomposite by MA/SPS
Kwon, Young-Soon,Kim, Ji-Soon,Kim, Hwan-Tae,Moon, Jin-Soo,D.V Dudina,O.I. Lomovsky The Korean Powder Metallurgy Institute 2003 한국분말재료학회지 (KPMI) Vol.10 No.6
Nano-sized $TiB_2$ was in situ synthesized in copper matrix through self-propagating high temperature synthesis (SHS) with high-energy ball milled Ti-B-Cu elemental mixtures as powder precursors. The size of $TiB_2$ particles in the product of SHS reaction decreases with time of preliminary mechanical treatment ranging from 1 in untreated mixture to 0.1 in mixtures milled for 3 min. Subsequent mechanical treatment of the product of SHS reaction allowed the $TiB_2$ particles to be reduced down to 30-50 nm. Microstructural change of $TiB_2$-Cu nanocomposite during spark plasma sintering (SPS) was also investigated. Under simultaneous action of pressure, temperature and electric current, titanium diboride nanoparticles distributed in copper matrix move, agglomerate and form a interpenetrating phase composite with a fine-grained skeleton.
Recursive formulas for the moments of queue length in the BMAP/G/1 queue
Dudin, A.,Klimenok, V.,Lee, M. IEEE 2009 IEEE communications letters Vol.13 No.5
<P>We present recursive formulas for the moments of the joint distribution of the queue length and the state of the underlying process in the BMAP/G/1 at the service completion and arbitrary time epochs.</P>