Papers by Enrique Lavernia
An Al-7.5 wt. % Mg alloy was ball-milled in liquid N2 for eight hours and its microstructures wer... more An Al-7.5 wt. % Mg alloy was ball-milled in liquid N2 for eight hours and its microstructures were investigated using transmission electron microscopy. Electron diffraction confirmed that the resulting powder is a supersaturated Al-Mg solid solution with a face-centered cubic structure. Three nanostructures with different grain size ranges and shapes were observed and the deformation mechanisms in these structures were found to be different. The reasons for the different deformation mechanisms were discussed. Keywords: Aluminum alloy; Cryogenic ball milling; Transmission electron microscopy; Microstructure.
searching existing data sources, gathering and maintaining the data needed, and completing and re... more searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggesstions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA, 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any oenalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.
Science Advances, 2018
High-entropy alloys (HEAs) are a class of metallic materials that have revolutionized alloy desig... more High-entropy alloys (HEAs) are a class of metallic materials that have revolutionized alloy design. They are known for their high compressive strengths, often greater than 1 GPa; however, the tensile strengths of most reported HEAs are limited. Here, we report a strategy for the design and fabrication of HEAs that can achieve ultrahigh tensile strengths. The proposed strategy involves the introduction of a high density of hierarchical intragranular nanoprecipitates. To establish the validity of this strategy, we designed and fabricated a bulk Fe25Co25Ni25Al10Ti15 HEA to consist of a principal face-centered cubic (fcc) phase containing hierarchical intragranular nanoprecipitates. Our results show that precipitation strengthening, as one of the main strengthening mechanisms, contributes to a tensile yield strength (σ0.2) of ~1.86 GPa and an ultimate tensile strength of ~2.52 GPa at room temperature, which heretofore represents the highest strength reported for an HEA with an appreciab...
Acta Materialia, 2016
In this study we report novel results obtained with an extruded fine-grained Mg-2.5 at.% Y alloy(... more In this study we report novel results obtained with an extruded fine-grained Mg-2.5 at.% Y alloy(FG Mg-2.5Y) exhibiting tension/compression yield symmetryand reduced strength differential, in addition to well-balanced strength and ductility. On the basis of detailed postmortem transmission electron microscopy studies, atom probe tomography, andelectron backscattered diffraction (EBSD) characterization,we propose that the presence of a supersaturated solid solution strengthening for basal slip, and the enhanced activity of prismatic slip are the major causes for the unusual mechanical behavior.
PUOIK reporting ouraen <or tn.s collection of information n estimated to average l hour per respo... more PUOIK reporting ouraen <or tn.s collection of information n estimated to average l hour per response, including the time tor reviewing instructions, searcmng e«.st.ng data «Jure«. oa?heV ncTind maintaining the data Weeded and competing and reviewing tne collection of information Send comments regarding this burden estimate or any other «o«t of this lo Xn 9 onnrorma,,onincluding suggestions for reducing this ourden. ?c Washington Headquarters Services. Directorate for ^m°ww<<« SFSSSj, U " ,eHe "°n Da.!» Highway. Su.te 1204. Arlington. 74 22202-4)02. and to the Office of Management and Budget. Paperwork Reduction Pr0|ect (0 704-0188). Washington. DC 20S03
Crystals, 2016
Micrometer-or submicrometer-sized metallic pillars are widely studied by investigators worldwide,... more Micrometer-or submicrometer-sized metallic pillars are widely studied by investigators worldwide, not only to provide insights into fundamental phenomena, but also to explore potential applications in microelectromechanical system (MEMS) devices. While these materials with a diminutive volume exhibit unprecedented properties, e.g., strength values that approach the theoretical strength, their plastic flow is frequently intermittent as manifested by strain bursts, which is mainly attributed to dislocation activity at such length scales. Specifically, the increased ratio of free surface to volume promotes collective dislocation release resulting in dislocation starvation at the submicrometer scale or the formation of single-arm dislocation sources (truncated dislocations) at the micrometer scale. This article reviews and critically assesses recent progress in tailoring the microstructure of pillars, both extrinsically and intrinsically, to suppress plastic instabilities in micrometer or submicrometer-sized metallic pillars using an approach that involves confining the dislocations inside the pillars. Moreover, we identify strategies that can be implemented to fabricate submicrometer-sized metallic pillars that simultaneously exhibit stabilized plasticity and ultrahigh strength.
Metallurgical and Materials Transactions A, 2015
A trimodal metal matrix composite (MMC) based on AA (Al alloy) 5083 (Al-4.4Mg-0.7Mn-0.15Cr wt.%) ... more A trimodal metal matrix composite (MMC) based on AA (Al alloy) 5083 (Al-4.4Mg-0.7Mn-0.15Cr wt.%) was synthesized by cryomilling powders followed by compaction of blended powders and ceramic particles using two successive dual mode dynamic (DMD) forgings. The microstructure consisted of 66.5 vol. % ultrafine grain (UFG) region, 30 vol. % coarse grain (CG) region and 3.5 vol. % reinforcing boron carbide particles. The microstructure imparted high tensile yield strength (581 MPa) compared to a conventional AA 5083 (242 MPa) and enhanced ductility compared to 100 % UFG Al MMC. The deformation behavior of the heterogeneous structure and the effects of CG regions on crack propagation were investigated using in situ scanning electron microscopy (SEM) micro-tensile tests. The micro-strain evolution measured using digital image
Metallurgical and Materials Transactions B, 2014
Pergamon Materials Series, 1999
Publisher Summary This chapter discusses the principle and variations of spray-forming. Spray for... more Publisher Summary This chapter discusses the principle and variations of spray-forming. Spray forming is also termed as spray atomization and deposition in the academic field as well as the industrial community. The spray deposition stage involves the collection of droplets in the spray cone onto a water-cooled substrate, forming a dense bulk material that is normally referred to as a deposit. Spray forming is normally carried out in an environmental chamber. The chamber is evacuated and back-filled, with a protective gas, such as N 2 , He, and Ar. The products of spray-forming include the bulk deposit and powders that are usually termed as oversprayed powders. In close-coupled spray-forming, the molten metal is released from the crucible through a delivery tube. In free-fall spray-forming, the molten metal is released from the bottom of the crucible, forming a stream. The molten metal stream travels downwards, through the atomizer unit, until it is atomized at a certain point below the atomizer. In reactive spray-forming, the atomization gas reacts with the droplets, forming inorganic phases, such as oxides, carbides, or nitrides.
Scripta Metallurgica et Materialia, 1995
The oxidation behavior of the nanocrystalline FeBSi alloy prepared using the crystallization meth... more The oxidation behavior of the nanocrystalline FeBSi alloy prepared using the crystallization method has been investigated. The results indicate that the microstructures of the materials have a strong effect on the oxidation behavior. Because of the unique nature of the microstructure, the nanocrystalline FeBSi alloy shows a significantly enhanced oxidation resistance over those of the amorphous and coarse-grained crystalline FeBSi alloys with the same composition.
Philosophical Magazine, 2014
ABSTRACT To gain fundamental insight into the relationship between length scales and mechanical b... more ABSTRACT To gain fundamental insight into the relationship between length scales and mechanical behaviour, Ni-Fe multilayered materials with a 5-μm-layer thickness and a modulated grain size distribution have been synthesized by pulsed electrodeposition. Microstructural studies by SEM and TEM reveal the alternating growth of well-defined layers with either nano (d = 16 nm) or coarse grains (d ≥ 500 nm). Room temperature tensile tests have been performed to investigate the mechanical response and understand the underlying deformation mechanisms. Tensile test results and fractographic studies demonstrate that the overall room temperature mechanical behaviour of the multilayered material, i.e. strength and ductility, is governed primarily by the layers containing nanocrystalline grains. The measured properties have been discussed in the context of modulated grain structure of the multilayered sample and contribution of each grain size regime to the overall strength and ductility.
Journal of Metastable and Nanocrystalline Materials, 2002
MRS Proceedings, 2004
The tensile behavior of bimodal nanocrystalline Al-7.5Mg alloys was investigated using experiment... more The tensile behavior of bimodal nanocrystalline Al-7.5Mg alloys was investigated using experiments and two-dimensional axisymmetric elastic-plastic finite element method (FEM). Cryomilled nanocrystalline powders blended with 15% and 30% unmilled coarse-grained powders were consolidated by hot isostatic pressing followed by extrusion to produce bulk bimodal nanocrystalline Al-7.5Mg alloys, which were comprised of nanocrystalline grains separated by coarse-grain regions. The calculated stress-strain curves have acceptable agreement with experimental curves of the bimodal structures. The bimodal Al-7.5Mg alloys show reasonable ductility while retaining enhanced strength compared to conventional alloys and nanocrystalline metals.
Acta Materialia, 2015
Palladium and its alloys are model systems for studying solid-state storage of hydrogen. Mechanic... more Palladium and its alloys are model systems for studying solid-state storage of hydrogen. Mechanical milling is commonly used to process complex powder systems for solid-state hydrogen storage; however, milling can also be used to evolve nanostructured powder to modify hydrogen sorption characteristics. In the present study, cryomilling (mechanical attrition milling in a cryogenic liquid) is used to produce nanostructured palladium-rhodium alloy powder. Characterization of the cryomilled Pd-10Rh using electron microscopy, X-ray diffraction, and surface area analysis reveals that (i) particle morphology evolves from spherical to flattened disk-like particles; while the (ii) crystallite size decreases from several microns to less than 100 nm and (iii) dislocation density increases with increased cryomilling time. Hydrogen absorption and desorption isotherms as well as the time scales for absorption were measured for cryomilled Pd-10Rh, and correlated with observed microstructural changes induced by the cryomilling process. In short, as the microstructure of the Pd-10Rh alloy is refined by cryomilling: (i) the maximum hydrogen concentration in the -phase increases, (ii) the pressure plateau becomes flatter, and (iii) the equilibrium hydrogen capacity increases at pressure of
Surface and Coatings Technology, 2006
This work describes recent progress in Cold Gas Dynamic Spraying process of conventional and nano... more This work describes recent progress in Cold Gas Dynamic Spraying process of conventional and nanocrystalline 2618 (Al-Cu-Mg-Fe-Ni) aluminum alloy containing Sc. As-atomized and cryomilled 2618 + Sc aluminum powders were sieved in two ranges of particle size (below 25 μm and between 25 and 38 μm), and sprayed onto aluminum substrates. The mechanical behavior of the powders and the coatings was studied using the nanoindentation technique, while the microstructure was analyzed using scanning and transmission electron microscopy. The influence of the powder microstructure, morphology and behavior during deposition on the coating properties was analyzed. It was concluded that the hard cryomilled particles do not experience extensive plastic deformation, and therefore failed to form a coating as dense as those produced using the gas-atomized spherical powder, despite the fact that the irregular shape cryomilled particles presented higher flight and impact velocities than the gas-atomized spherical particles. It was also observed that the influence of the particle morphology on the particle velocities is more pronounced for the larger particle size range (between 25 and 38 μm).
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Papers by Enrique Lavernia