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On the Densification Kinetics of Metallic Powders Under Hot Uniaxial Pressing
J. M. Montes,F. G. Cuevas,J. Cintas,F. Ternero,E. S. Caballero 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.3
A new model undertaking the densification kinetics of uniaxially pressed metallic powders at constant temperature is proposed. This model is developed according to the power law of creep, and the expression of the ‘net pressure’ derived by theauthors in a previous work. This net pressure describes the ‘geometrical hardening’ experienced by the powder mass, duringcompression. In order to validated the model three different powders were uniaxially pressed, aluminium, tin and lead, beingobtained data from hot compaction experiments. The similarity between the model predicted curves and the experimentaldata is quite acceptable. In addition, the goodness of the model is contrasted with two other theoretical models addressing thesame problem. The approach developed can be useful to model hot uniaxial pressing and electrical consolidation processes,which start with loose powders, i.e., not previously cold compacted powders.
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Barrera, Elixir William,Pujol, Marí,a Cinta,Dí,az, Francesc,Choi, Soo Bong,Rotermund, Fabian,Park, Kyung Ho,Jeong, Mun Seok,Cascales, Concepció,n IOP Pub 2011 Nanotechnology Vol.22 No.7
<P>Yb<SUP>3 + </SUP> and Ln<SUP>3 + </SUP> (Ln<SUP>3 + </SUP> = Er<SUP>3 + </SUP> or Tm<SUP>3 + </SUP>) codoped Lu<SUB>2</SUB>O<SUB>3</SUB> nanorods with cubic <img SRC='http://ej.iop.org/images/0957-4484/22/7/075205/nano368878ieqn1.gif' ALIGN='MIDDLE' ALT='Ia\bar 3 '/> symmetry have been prepared by low temperature hydrothermal procedures, and their luminescence properties and waveguide behavior analyzed by means of scanning near-field optical microscopy (SNOM). Room temperature upconversion (UC) under excitation at 980 nm and cathodoluminescence (CL) spectra were studied as a function of the Yb<SUP> + </SUP> concentration in the prepared nanorods. UC spectra revealed the strong development of <img SRC='http://ej.iop.org/images/0957-4484/22/7/075205/nano368878ieqn2.gif' ALIGN='MIDDLE' ALT='\mathrm {Er}^{3+}\,^{4}\mathrm {F}_{9/2}\to {}^4\mathrm {I}_{15/2} '/> (red) and <img SRC='http://ej.iop.org/images/0957-4484/22/7/075205/nano368878ieqn3.gif' ALIGN='MIDDLE' ALT='\mathrm {Tm}^{3+}\,{}^{1}\mathrm {G}_{4} \to {}^{3}\mathrm {H}_{6} '/> (blue) bands, which became the pre-eminent and even unique emissions for corresponding nanorods with the higher Yb<SUP>3 + </SUP> concentration. Favored by the presence of large phonons in current nanorods, UC mechanisms that privilege the population of <SUP>4</SUP>F<SUB>9/2</SUB> and <SUP>1</SUP>G<SUB>4</SUB> emitting levels through phonon-assisted energy transfer and non-radiative relaxations account for these observed UC luminescence features. CL spectra show much more moderate development of the intensity ratio between the <img SRC='http://ej.iop.org/images/0957-4484/22/7/075205/nano368878ieqn2.gif' ALIGN='MIDDLE' ALT='\mathrm {Er}^{3+}\, {}^{4}\mathrm {F}_{9/2} \to {}^4\mathrm {I}_{15/2} '/> (red) and <SUP>2</SUP>H<SUB>11/2</SUB>, <img SRC='http://ej.iop.org/images/0957-4484/22/7/075205/nano368878ieqn4.gif' ALIGN='MIDDLE' ALT='^{4}\mathrm {S}_{3/2}\to {}^{4}\mathrm {I}_{15/2} '/> (green) emissions with the increase in the Yb<SUP>3 + </SUP> content, while for Yb<SUP>3 + </SUP>, Tm<SUP>3 + </SUP>-codoped Lu<SUB>2</SUB>O<SUB>3</SUB> nanorods the dominant CL emission is <img SRC='http://ej.iop.org/images/0957-4484/22/7/075205/nano368878ieqn5.gif' ALIGN='MIDDLE' ALT='\mathrm {Tm}^{3+}\,{}^{1}\mathrm {D}_{2}\to {}^{3}\mathrm {F}_{4} '/> (deep-blue). Uniform light emission along Yb<SUP>3 + </SUP>, Er<SUP>3 + </SUP>-codoped Lu<SUB>2</SUB>O<SUB>3</SUB> rods has been observed by using SNOM photoluminescence images; however, the rods seem to be too thin for propagation of light. </P>
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Modelling and Simulation of the Electrical Resistance Sintering Process of Iron Powders
J. M. Montes,F. G. Cuevas,F. J. V. Reina,F. Ternero,R. Astacio,E. S. Caballero,J. Cintas 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.7
In this paper, the process known as Electrical Resistance Sintering under Pressure is modelled, simulated and validated. Thisconsolidation technique consists of applying a high-intensity electrical current to a metallic powder mass under compression. The Joule effect acts heating and softening the powders at the time that pressure deforms and makes the powder mass todensify. The proposed model is numerically solved by the finite elements method, taking into account the electrical–thermal–mechanical coupling present in the process. The theoretical predictions are validated with data recorded by sensorsinstalled in the electrical resistance sintering equipment during experiments with iron powders. The reasonable agreementbetween the theoretical and experimental curves regarding the overall porosity and electrical resistance suggests that themodel reproduces the main characteristics of the process. Also, metallographic studies on porosity distribution confirm themodel theoretical predictions. Once confirmed the model and simulator efficiency, the evolution of the temperature and theporosity fields in the powder mass and in the rest of elements of the system can be predicted. The influences of the processingparameters (intensity, time and pressure) as well as the die material are also analyzed and discussed.
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Simulation of the Electrical Resistance Sintering of Hardmetal Powders
Juan Manuel Montes,Francisco J. de la Viña,Íñigo Agote,Thomas Schubert,Francisco G. Cuevas,Yadir Torres,José María Gallardo,Jesús Cintas 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.2
The simulation of the electrical resistance sintering (ERS) of hardmetal powders has been studied. The ERS process canproduce a quick consolidation of electrical conductive powders by the simultaneous application of pressure and electricalcurrent. A model of the process has been developed, integrating three actions, namely, thermal, mechanical and electrical,and taking into account the nature of both the powders and the die where powders are placed. The model has been implementedin COMSOL Multiphysics, a finite element commercial program. This paper deals with the model fundamentals andhardmetal particular aspects, such as modelling properties of mixed powders and its thermal behaviour. Other parameters inthe model have been tuned to optimally fit the initial experimental data. To check simulation results, measurable parametershave been monitored during experimental tests with WC–6 wt% Co. Once the model was completed and put to work, resultsare discussed.
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