Gonzalez-Ojeda, Roberto
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Preferred name
Gonzalez-Ojeda, Roberto
Official Name
Gonzalez Ojeda, Roberto
Alternative Name
robglez
González-Ojeda, R.
Main Affiliation
ORCID
Scopus Author ID
56314856300
Researcher ID
DTL-2716-2022

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Now showing 1 - 10 of 36
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Tribo-corrosion protection of valves and rotors using cermet layers applied with HVOF

2017 , Quintana, María José , Gonzalez-Ojeda, Roberto , Fernández, D. , Verdeja, Luis Felipe

Protection of conventional steel parts in equipment that must withstand wear of the tribo-corrosion type (combination of heat and an aqueous medium) can be achieved by High Velocity Oxy-Fuel (HVOF) techniques, applying carbide-based cermet layers which decrease tribological and corrosion mechanisms. Three different carbide layers were applied to a ferritic-pearlitic steel in order to characterize properties such as sliding friction coefficient, phase identification, adhesion to the substrate, porosity, layer thickness and wear mechanisms. An example of a real rotatory equipment after a working campaign, both with and without protective layer is presented. The capacity of the protective layer to extend the life of parts like the one analyzed is evident even if zones of the layer are detached during the campaign. © 2017, Pleiades Publishing, Ltd.

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Microstructures of a pressure die cast Al-8.5%Si-3.5%Cu alloy

2017 , Barbés Fernández, Miguel Ángel , 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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Presintering of TiCN-TiC-WC-Cr 3 C 2 -Ni cermets under N 2 -H 2 atmospheres

2017 , López-Ezquerra, Belén , Gonzalez-Ojeda, Roberto , Iparraguirre, I. , Rodríguez, N. , 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

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Wear in ultrafine hardmetal mills manufactured by sinter + HIP

2006-12-01 , Ordóñez, Alejandro , Gonzalez-Ojeda, Roberto , Sánchez-Moreno, José Manuel

Ultrafine WC-Co milling tools were wear-tested in finishing machining conditions. Mills manufactured in the laboratory followed the powder metallurgy route for ultrafine grades. Total density in hardmetal grades of 0.2 and 0.4 μm was achieved through the Sinter + HIP technique. Wear in laboratory mills was compared with wear in coarse and ultrafine grade commercial mills. All mills cutting edges suffered wear mainly in the abrasive and chipping form. Chipping was excessive and peculiar in form in the laboratory mills; a slight presence of the fragile η phase was discovered. Laboratory mills showed similar wear to the commercial coarse grades, and much more than that of commercial ultrafine grades. A lack of toughness is suggested due to a small difference in the WC mean grain size, in the Co mean free path (λ) and in its distribution: homogeneous in laboratory mills and heterogeneous in the commercial ones. ©Metal Powder Industries Federation (MPIF)

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Mechanical behaviour of thermomechanically produced ultrafine grained dual-phase steels

2014 , Gonzalez-Ojeda, Roberto , García García, José Ovidio , Verdeja González, Luis Felipe , Quintana, María José , Verdeja González, José Ignacio

Dual-phase (DP) steels are an excellent alternative in the production of automotive parts that require high mechanical resistance, high impact strength and elevated elongation. These materials are produced using low alloy steels as a basis, reducing costs and resulting in a combination of martensite and ferrite structures with ultrafine grain size. These characteristics are achieved through strict control of rolling conditions, strain rate, cooling rate and coiling temperature. This work presents the results of tension testing of two types of DP steels, along with microstructural characterisation, in order to understand the effect of the advanced thermomechanical controlled rolling processes on the formation of the microstructure and resulting mechanical properties.

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Material wear in blast furnace crucibles

1998-05 , Verdeja González, Luis Felipe , Alonso, A. , Gonzalez-Ojeda, Roberto

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HIP after sintering of ultrafine WC–Co hardmetals

2005 , Sánchez, J. M. , Ordóñez, Alejandro , 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.

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Using FEM to determine temperature distribution in a blast furnace crucible

2000 , Verdeja, Luis Felipe , Gonzalez-Ojeda, Roberto , Ordóñez, Alejandro

Temperature distribution in the crucible of a blast furnace is an important operation variable that is a function of the materials used in its construction, temperatures reached in the pig iron-refractory interface, and cooling-system performance. Defining the crucible zones where high shear and tensile stresses are reached is an important step in developing a tribological model to understand and predict high wear zones and crucible life. In this work, temperature distribution was simulated using the finite-element method for a blast furnace built following the ceramic solution (oxide and nitride ceramics in contact with the pig iron and carbon and microporous graphite blocks in contact with the refrigeration system).

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Superplasticity of ultrafine grained low-carbon HSLA steels

2012 , Verdeja González, José Ignacio , Quintana, María José , García García, José Ovidio , Verdeja González, Luis Felipe , Gonzalez-Ojeda, Roberto , Fernández Fernández, Sara

Steels with ultrafine grained structure may present superplastic behavior at specific temperatures and strain rates that allow the grain boundary sliding mechanisms to be activated. The work presents high temperature tension tests in a low carbon, low alloy steel obtained by advanced thermomechanical controlled rolling processes, showing at 800°C elongations as high as 200%. The microstructure of the steel was analyzed in order to identify ferrite and pearlite grain boundaries, and their interaction after the specimens were deformed, showing intergranular decohesions, restored ferrite grains and elimination of banded structure, which are evidence of superplastic mechanisms in this material which is, in fact, ultrafine grained as demonstrated by quantitative metallographic techniques and grain size distribution analysis.

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Influence of strain rate and heat treatments on tensile and creep properties of Zn-0.15Cu-0.07Ti alloys

2016 , Quintana, María José , García, José Ovidio , Gonzalez-Ojeda, Roberto , Verdeja, José Ignacio

The use of Cu and Ti in Zn alloys improves mechanical properties as solid solution and dispersoid particles (grain refiners) may harden the material and reduce creep deformation. This is one of the main design problems for parts made with Zn alloys, even at room temperature. In this work the mechanical behavior of a Zn-Cu-Ti low alloy is presented using tensile tests at different strain rates, as well as creep tests at different loads to obtain the value of the strain rate coefficient m in samples parallel and perpendicular to the rolling direction of the Zn strip. The microstructure of the alloy in its raw state, as well as heat treated at 250°C, is also analyzed, as the banded structure produced by rolling influences the strengthening mechanisms that can be achieved through the treatment parameters. © The author; licensee Universidad Nacional de Colombia.

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