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Differences in Defect Distribution Across Scan Strategies in Electron Beam AM Ti-6Al-4V : The fraction and size of pores present in EBM Ti-6Al-4V specimens varies depending on the melting strategy used, whether linear raster melting or point melting
(2021)
Quintana, María José
;
O’Donnell, Katie
;
Kenney, Matthew J.
;
Collins, Peter C.
In recent years, additive manufacturing (AM) has begun to displace traditional manufacturing techniques for specific applications. Notable benefits of AM include reduced times from design to product, an improved buy-tofly ratio, lower waste, and the ability to produce complex geometries[1,2]. An additional benefit of additive manufacturing is the variety of manufacturing processes that span across heat source (e.g., laser, electron beam, plasma), input material type (e.g., powder, wire), atmosphere, and the number of axes of control among others[2-4]. This variability in processing route means that a process can be identified and optimized for a class of products or parts. Despite these various advantages, one of the primary drawbacks of AM processes is porosity within builds, which ultimately reduces the ability of a part to withstand tensile stresses and can lead to premature failure[4-6]. Copyright 2021 ASM International.
Scopus© Citations 3 24 1
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Solidification and Solid-State Transformations of Metals and Alloys
(Elsevier Inc., 2017)
Quintana, María José
;
Pero-Sanz, José Antonio
;
Verdeja González, Luis Felipe
Solidification and Solid-State Transformations of Metals and Alloys describes solidification and the industrial problems presented when manufacturing structural parts by casting, or semi-products for forging, in order to obtain large, flat or specifically shaped parts. Solidification follows the nucleation and growth model, which will also be applied in solid-state transformations, such as those taking place because of changes in solubility and allotropy or changes produced by recrystallization. It also explains the heat treatments that, through controlled heating, holding and cooling, allow the metals to have specific structures and properties. It also describes the correct interpretation of phase diagrams so the reader can comprehend the behaviour of iron, aluminium, copper, lead, tin, nickel, titanium, etc. and the alloys between them or with other metallic or metalloid elements. This book can be used by graduate and undergraduate students, as well as physicists, chemists and engineers who wish to study the subject of Metallic Materials and Physical Metallurgy, specifically industrial applications where casting of metals and alloys, as well as heat treatments are relevant to the quality assurance of manufacturing processes. It will be especially useful for readers with little to no knowledge on the subject, and who are looking for a book that addresses the fundamentals of manufacturing, treatment and properties of metals and alloys. Uses theoretical formulas to obtain realistic data from industrial operations. Includes detailed explanations of chemical, physical and thermodynamic phenomena to allow for a more accessible approach that will appeal to a wider audience. Utilizes micrographs to illustrate and demonstrate different solidification and transformation processes. © 2017 Elsevier Inc. All rights reserved.
13 1
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Dmaic of structural steel parts through FEM and DOE
(2016)
Gonzalez-Ojeda, Roberto
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Quintana, María José
;
Verdeja, Luis Felipe
DMAIC in the automotive sector is applied to the design and manufacturing processes of structural steel parts in order to assess variability in mechanical properties of the raw materials, use of different types of steel in the same part, modifications in thickness of the steel sheet and even changes in geometry to produce lighter and stronger parts. The work presents an example of three stamped automotive structural components, mechanically interacting together when deformed under load. Minitab design of experiments module was used to evaluate two level factors, one of them being the thickness of each part, and the other the material properties: DP600, DP780 steel or a boron-based steel alloy. A FEM model of the three parts, with structural supports and loads, was performed to evaluate displacement of the system, max. equivalent stress, strain and total weight, allowing data correlation to determine best practices to accomplish low weight, high stiffness designs. Copyright © 2016 MS&T16®.
8 1
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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
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Quintana, María José
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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.
43 2
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Microstructural changes of a construction steel caused by hot deformation
(2013)
Verdeja González, José Ignacio
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Quintana, María José
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Gonzalez-Ojeda, Roberto
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Verdeja González, Luis Felipe
A construction steel (shipbuilding strip) obtained by Advanced Thermomechanical Controlled Rolling Processes presents a room temperature banded ferrite-pearlite microstructure, and when superplastically deformed at 800°C with a strain rate of 5.85x10-5 s-1, the bands disappear as there is grain boundary sliding and grain cluster rotation. Nevertheless, the superplastic deformation does not imply a decrease in mechanical properties, as room temperature tests with strain rates of 1.46x10-3 s -1 with the steel previously deformed in superplastic conditions (until a 110% of straining) result in similar mechanical data. If the steel is deformed at 750°C with low strain rates, cooling results in a microstructure formed only by ferrite and carbides (the pearlitic phase disappears). This behavior may be explained, from a thermodynamical point of view, by the effect of negative hydrostatic pressure during the tensile test and the pronounced ferrite- and carbide-former capacity of Ti and Nb microalloying elements. The samples, tensile tested, in both the hot rolled raw state and superplastically deformed and then room temperature tested, show in the fracture surface SEM analysis almost identical features: decohesions surrounding MnS and (C,N)(Ti,Nb) precipitates and between ferrite and pearlite grains, as well as bedding.
6 2
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Superplasticity of ultrafine grained low-carbon HSLA steels
(2012)
Verdeja González, José Ignacio
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Quintana, María José
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García García, José Ovidio
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Verdeja González, Luis Felipe
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Gonzalez-Ojeda, Roberto
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.
8 1
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Dual-phase ultrafine grained steels produced by controlled rolling processes
(2011)
Quintana, María José
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Gonzalez-Ojeda, Roberto
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Verdeja González, Luis Felipe
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Verdeja González, José Ignacio
Double-phase 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 sizes. These characteristics are accomplished through a strict control of rolling conditions: strain rate, cooling rate and direct quenching. This work presents the results of tension testing of two types of double phased steels, along with microstructural characterization, in order to understand the effect of the advanced thermomechanical controlled rolling processes on the formation of the microstructure and the resulting mechanical properties.
7 2
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Superplastic HSLA steels: Deformation and Failure
(2012)
Fernández, S.
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Verdeja González, José Ignacio
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Quintana, María José
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Gonzalez-Ojeda, Roberto
Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.
5 1
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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
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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 9 1
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Superplastic HSLA Steels: Microstructure and Failure
(2013)
Fernández, Sara
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García García, José Ovidio
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Verdeja González, Luis Felipe
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Verdeja González, José Ignacio
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Quintana, María José
Certain materials can show superplasticity when traction tested at temperatures higher than 50% of their melting point and with low strain rates ( < 10−2 s−1), showing very high elongations (>100%) without localized necking and mainly intergranular fractures. This behavior requires that the starting grain size is small (<10 μm) so the flow of matter can be non-homogeneous (sliding and rotating of the grain boundaries, accommodated by diffusion). This work presents the superplastic characteristic of shipbuilding steel deformed at 800 °C and a strain rate slower than 10−3 s−1. The fine grain size (5 μm) is obtained when using Nb as a microalloying element and manufactured by controlled rolling processes (three stages). After the superplastic deformation, the steel presents mixed fractures: by decohesion of the hard (pearlite and carbides) and ductile (ferrite) phases and by intergranular sliding of ferrite/ferrite and ferrite/pearlite, just as it happens in stage III of the creep behavior. This is confirmed through the Ashby–Verrall model, according to which the dislocation creep (power-law creep) and diffusion creep (linear-viscous creep) occur simultaneously.
Scopus© Citations 4 7 1

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