Gonzalez-Ojeda, Roberto

Main Affiliation

Facultad de Ingeniería - CampCM

Preferred name

Official Name

Gonzalez Ojeda, Roberto

ORCID

0000-0003-2319-1631

Researcher ID

DTL-2716-2022

Scopus Author ID

56314856300

Now showing 1 - 10 of 38

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Warm-stamping mechanical behavior and microstructural characterization of Al-Si metal sheets using water refrigerated tooling
(IEEE, 2026)
Estrada-Warn, Paola
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Garcia-Santibañez, G. J.
;
Jauregui-Pablos, M.
;
Vazquez-Gomez-Orduña, Sebastián
;
Gonzalez-Ojeda, Roberto
The use of water refrigerated tooling in a laboratory scale was used to simulate conditions of warm (500°C) stamping of aluminum plates with 0.8 mm in thickness. The work presents load-displacement curves of room temperature and heat treated samples during stamping at 120 and 240 mm/min, effect of the treatment in the anisotropic characteristics of the rolled sheet plate and electron microscopy analysis along with element detection, as this alloy contains small amounts of silicon. The processes resembles a solution treatment and, thus, also an aging treatment at 120°C for 12 h was carried out in order to understand the application possibilities of the manufacturing process in the automotive or aero-space industry. © The authors © IEEE.
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Effect of pressure in the microstructure of die cast Al-8.5Si-3.5cu alloys
(2014)
Barbés Fernández, Miguel Ángel
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Verdeja González, José Ignacio
;
Quintana, María José
;
Verdeja González, Luis Felipe
;
Gonzalez-Ojeda, Roberto
The microstructure of Pressure Die Casting of an Al-8.5 Si-3.5 Cu alloy used for clean room tiles shows amount of constituents (eutectic and Si phases) that do not correspond to the ones indicated by the phase diagram. Furthermore, there are differences in amount of constituents between the core and the surface zones of parts produced by this process. The work presents quantitative microstructural analysis of this type of industrially produced part, and as a possible cause for these differences, simulations of the effect of pressure on the eutectic (temperature and chemical composition) in the Al-Si system. As the production rate of these parts is very high, and solidification is very fast, microstructural heterogeneity may be related to local entrapment of gasses unable to escape during casting.
2 9
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Machinability Improvement Through Heat Treatment In 8620 Low-Carbon Alloyed Steel
(2009)
Verdeja, Luis Felipe
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Verdeja, José Ignacio
;
Gonzalez-Ojeda, Roberto
The effect of different heat treatments is evaluated on SAE 8620 low-carbon alloyed steel by means of drilling tests. Improving machinability through prior heat treatment in steels used for nitro-carburizing surface treatments is very important in the manufacturing of large series of parts, due to its impact in production costs. This is the case for the commonly used SAE 8620 grade, in its carburized and quenched and tempered state, for the production of gears, shafts and other transmission box components for the automobile industry. The machinability of the steel, determined by simple drilling tests (which are typical in industry labs), is a function of microstructure, which is determined by the state in which the steel is received and/or heat treatments prior to carburizing. This work shows that by employing some inter-critic annealing treatments, followed by sub-critic isothermal ones, the machinability of 8620 steel can be improved by ∼16% over the typical as-received cold drawn state.
Scopus© Citations 6 2 33
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Material wear in blast furnace crucibles
(1998-05)
Verdeja González, Luis Felipe
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Alonso, A.
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Gonzalez-Ojeda, Roberto
5 11
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Structural Ultrafine Grained Steels Obtained by Advanced Controlled Rolling
(2013)
García García, José Ovidio
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Barbés Fernández, Miguel Ángel
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Verdeja González, Luis Felipe
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Verdeja González, José Ignacio
;
Gonzalez-Ojeda, Roberto
Steels with ultrafine grains (lower than 5 μpa), which usually known as ultrafine ferrite or ultrafine grained materials, are presently the object of intense research, because of the improvement in resistance and fracture toughness they may reach compared to conventional steels (with grain sizes above this value). It is shown that the forenamed steels designated in the Euronorm EN 10149-2, which are manufactured by advanced techniques of controlled rolling and mainly used in automotive industry, have an ultrafine grain size in the range of 2. 5 to 3. 5 μm, and with elastic yield stresses higher than 400 MPa. Based on the Morrison-Miller criterion, it is shown that values of the strain-hardening coefficient lower than 0. 08 would make the industrial application of these steels unfeasible.
Scopus© Citations 3 1 25
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Presintering of TiCN-TiC-WC-Cr 3 C 2 -Ni cermets under N 2 -H 2 atmospheres
(2017)
López-Ezquerra, Belén
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Gonzalez-Ojeda, Roberto
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Iparraguirre, I.
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Rodríguez, N.
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Sánchez-Moreno, José Manuel
C/N ratios in TiCN-TiC-WC-Cr3C2-Ni cermets can be intentionally modified by changing the composition of the presintering atmosphere. This affects not only the sinterability but also the final microstructure of these materials. Melting occurs at lower temperatures as the nitrogen content of the presintering atmosphere rises. However, the final densities are lower due to the precipitation of free carbon. Grain growth of the carbonitride phase is accelerated in samples presintered in N2 due to the activation of solution reprecipitation kinetics. Finally, the precipitation of the Cr-rich M7C3 carbide can also be controlled by the appropriate selection of the presintering atmosphere up to 7.8 wt.% Cr contents. © 2016 Elsevier Ltd
Scopus© Citations 14 1 17
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Ultrafine-grain Steels: Mechanical Behavior
(2016)
Quintana Hernández, María José
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Gonzalez-Ojeda, Roberto
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MARÍA JOSÉ QUINTANA HERNÁNDEZ;576914
In recent years, both the steelmaking industry and laboratories in different parts of the world, have shown an increasing interest in reaching an industrial-level production of ultrafine grained steels (also known as ultrafine ferrite), which have a grain size d lower than 5 μm, and enhanced mechanical resistance and fracture toughness. At room temperature, the capacity of the material to be deformed during bending or drawing operations (typical of requirements for automotive parts applications) depends on the interaction of a hard and a soft phase in the microstructure. On the other hand, at high temperatures, these steels may show superplastic behavior if deformed at a precise combination of temperature and strain rate.
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HIP after sintering of ultrafine WC–Co hardmetals
(2005)
Sánchez, J. M.
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Ordóñez, Alejandro
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Gonzalez-Ojeda, Roberto
This paper analyses the changes induced by HIP after sintering on the microstructure and mechanical properties of WC–7wt.%Co ultrafine hardmetal grade. The well known correlation between porosity reduction and fracture strength improvement is confirmed in these compositions, this being more effective at HIP temperatures above the eutectic point of the alloy. In absence of GGI, hardness decreases continuously as the HIP temperature increases. However, for specimens containing VC and Cr3C2 additions, hardness increases as the HIP temperature increases from 1200 °C to 1400 °C. This anomalous trend, confirmed by WC grain size observations, could be related to the activation of coalescence mechanisms during solid state HIPing, which are inhibited by the presence of a liquid phase.
2 13Scopus© Citations 42
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Microstructures of a pressure die cast Al-8.5%Si-3.5%Cu alloy
(2017)
Barbés Fernández, Miguel Ángel
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Quintana, María José
;
Verdeja González, José Ignacio
;
Gonzalez-Ojeda, Roberto
Quantitative microstructural measurements of constituents of an Al-Si-Cu alloy, used to manufacture a part with thin sections by Pressure Die Casting (PDC), do not correspond to phase diagram calculations. A simulation of the liquid velocity when filling the mold was made in order to understand the relation between this parameter and pressure, cooling rate and the eutectic amount and morphology. Also, the microstructures of the same alloy solidified in a ceramic crucible (low cooling rate) and in a metal flask (high cooling rate) were compared to those obtained by PDC to analyze the role of pressure on the displacement of eutectic composition and formation of different eutectic morphologies. The amount of constituents varies with distance from the mold walls, producing higher or lower pressure zones, which may be estimated from the Al-Si phase diagram simulation at different pressures. As these pressures must be very high (∼ 2 GPa), a possible explanation for the displacement of the eutectic point is the combination of high cooling rate of the manufacturing process, entrapment of gases during solidification and influence of the alloying elements.
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New binder phases for the consolidation of TiB2 hardmetals
(1996)
Gonzalez-Ojeda, Roberto
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Barandika, M.G.
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Oña, D.
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Sánchez, J.M.
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Villellas, A.
New TiB2-based cermets have been consolidated by hot isostatic pressing of powder mixtures of TiB2 and metallic alloys based on Fe, Ni and Co additions. Relevant thermodynamic aspects of the systems B-Ti-Ni, B-Ti-Fe and B-Ti-Co, essential for avoiding the formation of extremely brittle secondary borides, especially the secondary boride M23B6, are discussed in this work. The role of contaminants like oxygen, carbon and nitrogen, which can also lead to the formation of these compounds is also explained. The hardness, toughness and cutting behaviour of the cermets produced with these new binder phases are comparable with the highest commercial WC-Co grades.
Scopus© Citations 49 1 7

Gonzalez-Ojeda, Roberto

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