Papers by Author: Nicolae Ghiban

Paper TitlePage

Authors: Florina Diana Dumitru, Brandusa Ghiban, Jose María Cabrera, Oscar Fabián Higuera-Cobos, Gheorghe Gurau, Nicolae Ghiban
Abstract: Being the lightest structural element, magnesium and its alloys has attracted significant interes in the last years, but because of its hexagonal close packed structure, magnesium presents relatively low strength and ductility. One of the methods to improve the mechanical properties of the processed materials is through Severe Plastic Deformation (SPD). ZK60 magnesium alloy samples were subjected to 4 passes of equal-channel angular pressing (ECAP) at a processing temperature of 250°C, following route A. The microstructure was determined with an Olympus BX51 optical microscope. Differential Scanning Calorimetry (DSC) was used to estimate the stored energy and the recrystallization temperature after each ECAP pass.
32
Authors: Brandusa Ghiban, Cristina Maria Borţun, Alexandru Ghiban, Nicolae Ghiban
Abstract: The present paper put in evidence the mechanical behaviour of some commercial dental cobalt alloys, after own classification. The experimental cobalt alloys were classified in according either with molybdenum content, or with Cr+Mo content. A hierarcy of the alloys was finally made. The fractographic surfaces were investigate both by stereomacroscopy and scanning electron microscopy, putting in evidence the main structural features.
175
Authors: Andreea Mihaela Magheru, Brandusa Ghiban, Nicolae Ghiban, Iulian Antoniac
Abstract: The present paper take in consideration two titanium alloys, with different molybdenum contents in order to show the corrosion behavior in Ringer body simulated fluid. The samples were corrosion tested in three states, respectively non-treated state, annealed at 850°C/1 h and annealed at 1050°C/1 h.
98
Authors: Nicolae Ghiban, Brandusa Ghiban, Nicolae Şerban, Alexandru Ghiban
Abstract: The present paper takes into consideration four titanium alloys from the system Ti-Mo, with different molybdenum contents in order to highlight the mechanical and structural behavior of them. The Dynamic Mechanical Analysis was made and this was in correlation with microstructural aspects and surface properties of the experimental alloys. The macrostructural features are the same for all Ti-Mo alloys after bending tests.
309
Authors: Nicolae Ghiban, Brandusa Ghiban, Nicolae Şerban, Alexandru Ghiban
Abstract: The present paper put in evidence the influence of applying different heat treatments on some metallic materials such as cobalt and titanium alloys, usualy used for medical applications. The alloys were cobalt base alloy type CoCrMo (22%Cr, 6%Mo, rest Co), in nontreated state, quenching at 1100°C /1h/aer, quenching at 1100°C /1h/air+ sensiblizing at 550°/4h/ air, 600°/4h/air and/or 650°C/4h/air and titanium base alloys - alloy TiMo0.3Ni0,7 (0.23%Mo, 0.72%Ni, Ti rest), alloy TiAl5Fe2V2Mo1,5 (1.52%Mo, 5.15%Al, 2.56%Fe, 2.35%V, Ti rest), each of them in non treated state, annealing at 1050°C/1h/air and annealing at 850°C/1h/air. Corrosion tests were made at potentiostat-galvanostat AUTOLAB, in Ringer solution (for both alloys) and NaCl infusion solution (only for cobalt base alloy) by drawing the polarization curves. Our conclusion is that by applying correct and proper heat treatments to both at cobalt alloys and in titanium alloys there is an improving of the corrosion resistance.
293
Authors: Alexandru Ghiban, Brandusa Ghiban, Cristina Maria Borţun, Nicolae Ghiban, Iulian Antoniac
Abstract: A new composition of a dental cobalt alloy was proposed from the system CoCrMoTi, which was compared with a commercial dental alloy, type Wironit. Some heat treatments were applied either for stabilizing the structure, or to simulate welding conditions (such as sensibilization treatments in the range of temperature about 550°C÷-650°C). Corrosion tests were made in two body simulated fluids, respectively infusion NaCl solution and Ringer solution. The results showed that titanium alloying may improve corrosion resistance of the alloy, and also the best state considering corrosion resistance is normalizing at 1100°C with one hour maintaining in air cooling at both alloys, with or without titanium. The worse corrosion resistance is obtained in sensibilized state.
93
Authors: Florina Diana Dumitru, Brandusa Ghiban, Jose María Cabrera, Oscar Fabián Higuera-Cobos, Gheorghe Gurau, Nicolae Ghiban
Abstract: In the last years many research efforts have been made in order to extend the application of wrought magnesium to structural components. One of the methods to improve the mechanical properties of the processed materials is through severe plastic deformation (SPD). ZK60 magnesium alloy samples were subjected to 6 passes of equal-channel angular pressing (ECAP) decreasing the temperature after the fourth pass, following an alternative route A. The structural characterization was realized by microstructural evolution using Oriented Image Microscopy (OIM) and XRD analysis. Differential Scanning Calorimetry (DSC) was used to estimate the stored energy and the recrystallization temperature after each ECAP pass.
169
Authors: Nicolae Serban, Doina Răducanu, Vasile Danut Cojocaru, Nicolae Ghiban
Abstract: Severe plastic deformation (SPD) has received enormous interest over the last two decades as a method capable of producing fully dense and bulk ultra-fine grained (UFG) and nanocrystalline (NC) materials. Significant grain refinement obtained by SPD leads to improvement of mechanical, microstructural and physical properties. Compared to classical deformation processes, the big advantage of SPD manufacturing techniques, represented in particular by equal channel angular pressing (ECAP) is the lack of shape-change deformation and the consequent possibility to impart extremely large strain. In ECAP processing, the workpiece is pressed through a die in which two channels of equal cross-section intersect at an angle of ϕ and an additional angle of ψ define the arc of curvature at the outer point of intersection of the two channels. As a result of pressing, the sample theoretically deforms by simple shear and retains the same cross-sectional area to allow repeated pressings for several cycles. A commercial AlMgSi alloy was investigated in our study. The specimens were processed at room temperature for multiple passes, using three different ECAP dies. All samples (ECAP processed and as-received) were subjected to metallographic analysis and mechanical testing. Several correlations between the main processing parameters and the resulting microstructural aspect and mechanical features for the processed material were established. It was shown that severe plastic deformation by means of ECAP processing can be used in aluminum alloys microstructural design as an advanced tool for grain refinement in order to attain the desired microstructure and mechanical properties.
143
Authors: Nicolae Şerban, Doina Răducanu, Nicolae Ghiban, Vasile Dănuţ Cojocaru
Abstract: The properties of ultra-fine grained materials are superior to those of corresponding conventional coarse grained materials, being significantly improved as a result of grain refinement. Equal channel angular pressing (ECAP) is an efficient method for modifying the microstructure by refining grain size via severe plastic deformation (SPD) in producing ultra-fine grained materials (UFG) and nanomaterials (NM). The grain sizes produced by ECAP processing are typically in the submicrometer range and this leads to high strength at ambient temperatures. ECAP is performed by pressing test samples through a die containing two channels, equal in cross-section and intersecting at a certain angle. The billet experiences simple shear deformation at the intersection, without any precipitous change in the cross-section area because the die prevents lateral expansion and therefore the billet can be pressed more than once and it can be rotated around its pressing axis during subsequent passes. After ECAP significant grain refinement occurs together with dislocation strengthening, resulting in a considerable enhancement in the strength of the alloys. A commercial AlMgSi alloy (AA6063) was investigated in this study. The specimens were processed for a number of passes up to nine, using a die channel angle of 110°, applying the ECAP route BC. After ECAP, samples were cut from each specimen and prepared for metallographic analysis. The microstructure of the ECAP-ed and as-received material was investigated using optical (OLYMPUS – BX60M) and SEM microscopy (TESCAN VEGA II – XMU). It was determined that for the as-received material the microstructure shows a rough appearance, with large grains of dendritic or seaweed aspect and with a secondary phase at grain boundaries (continuous casting structure). For the ECAP processed samples, the microstructure shows a finished aspect, with refined, elongated grains, also with crumbled and uniformly distributed second phase particles after a typical ECAP texture.
3
Authors: Nicolae Ghiban
Abstract: Present paper presents the results concerning the modeling process of extrusion of a profile type “Yalle body”. COSMOS soft was used in order to simulate the extrusion process. 3D model contains elements type SOLID, witch simulates the nonlinear behavior in the field of elasticplastic domain. The constitutive equation of Iliusin and Dracker-Prager relation and Von Misses criterion were used in simulation. The three dimensions model contains 1504 nods and 1750 elements in two different position of the die (optimum position and “out of optimum position”). For both of die positions were presented variation of equivalent total stresses, tangential stresses in different steps (1st step, critical step, and 20th step, by dividing the whole extrusion process in equal steps).
181
Showing 1 to 10 of 14 Paper Titles