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Martinez Saez, Enrique

Publications and source records attributed to Martinez Saez, Enrique.

18 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Chemical short-range order in derivative Cr–Ta–Ti–V–W high entropy alloys from the first-principles thermodynamic study

The development of high-entropy alloys (HEAs) focuses on exploring compositional regions in multi-component systems with all alloy elements in equal or near-equal atomic concentrations. Initially it was based on the main idea that high mixing configurational entropy contributions to the alloy free energy could promote the formation of a single solid solution phase. By using the ab-initio based Cluster Expansion (CE) Hamiltonian model constructed for the quinary bcc Cr–Ta–Ti–V–W system in combination with Monte Carlo (MC) simulations, we show that the phase stability and chemical short-range order (SRO) of the equiatomic quinary and five sub-quaternary systems, as well as their derivative alloys, can dramatically change the order–disorder transition temperatures (ODTT) as a function of alloy compositions. In particular, it has been found, that the equiatomic quaternary Ta–Ti–V–W and Cr–Ta–Ti–W alloys had the lowest order–disorder transition temperature (500 K) among all the analysed equiatomic compositions. In all investigated alloy systems, the strongest chemical ordering has been observed between Cr and V, which led to the conclusion that decreasing the concentration of either Cr or V might be beneficial in terms of decreasing the ODTT. It also predicts that increasing concentration of Ti significantly decreases the ODTT. Our analysis of chemical SRO as a function of alloy composition allows to understand the microstructure evolution of HEAs as a function of temperature in excellent agreement with available experimental observations. Importantly, our free energy of mixing and SRO calculations predict that the origin of precipitates formed by Cr- and V-rich in the sub-quaternary Cr–Ta–V–W system is driven by the thermodynamics. The modelling results are in an excellent agreement with experimental observation of Cr and V segregation in the W 0.38 Ta 0.36 Cr 0.15 V 0.11 alloy which in turns shows an exceptional radiation resistance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Does sink efficiency unequivocally characterize how grain boundaries impact radiation damage?

The role of grain boundaries in limiting irradiation damage in nanocrystalline materials is often correlated with the grain boundary sink efficiency. Here, we demonstrate on a tungsten material system (which has very distinct vacancy and interstitial mobilities) that sink efficiency does not unequivocally describe how grain boundaries impact irradiation damage. Rather, it reflects a particular defect diffusion equation that can change if any of the bulk conditions change. Even when denuded zone formation does not occur and grain boundaries have zero sink efficiencies, grain boundaries still impact the performance of nanocrystalline materials under irradiation by acting as a saturable defect storage site. However, denuded zone formation can occur under a necessary requirement of extra defect recombination at the grain boundaries (which, for example, is not possible when vacancy migration does not occur). These insights provide answers to several outstanding questions regarding the sink efficiency of a grain boundary and assist in parametrizing the role of grain boundaries in limiting irradiation damage in nanocrystalline materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The Kinetic Monte Carlo Algorithm in Materials Science: Study of Radiation-Induced Segregation in Fe-Cr alloys [Slides]

KMC is a flexible tool applicable to many fields in Material Science. Continuum models need free energies and transport coefficients. Atomistic KMC: an efficient tool to study RIS especially when coupled with ab initio calculations. AKMC generates crucial data to incorporate in Phase Field methods. AKMC shows that RIS profiles depend strongly on the interface spacing. Drawbacks include that it is time consuming and limited to relatively short times. Self-Consistent Mean-Field (SCMF) is an alternative approach to calculate phenomenological coefficients that avoids the KMC caveats.

36 MATERIALS SCIENCE↗
DOE OSTI2018

How relative defect migration energies drive contrasting temperature-dependent microstructural evolution in irradiated ceramics

Ceramic materials have become widely used in various fields of material science, and ceramic oxides such as cubic zirconia (c- ZrO 2 ) and magnesia (MgO) are candidate materials for nuclear energy applications. For the corresponding in-service conditions of these materials, there is a crucial need in studies at moderate or high temperatures of the physical phenomena underlying the damage buildup under irradiation. Here in the present work, we show, using x-ray diffraction, that these two materials exhibit a similar damage accumulation process under ion irradiation at fixed temperature. However, they display an unexpected opposite damaging rate to changes in the irradiation temperature. In fact, as the temperature is increased, the final damage state is reached earlier in c- ZrO 2 while it is delayed in MgO. Rate equation cluster dynamics simulations show that defect clustering is favored over defect recombination in c- ZrO 2 , but the situation is reversed for MgO, explaining the observed opposite response to temperature of the two materials. This contrasting behavior can be rationalized in terms of nonequivalent interstitial versus vacancy defect migration energies in MgO. We finally demonstrate that these results allow for a qualitative prediction of the evolution of the experimental irradiation-induced disorder with temperature, henceforth potentially reducing the cost in selecting and developing ad hoc materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Structure and Mobility of Dissociated Vacancies at Twist Grain Boundaries and Screw Dislocations in Ionic Rocksalt Compounds

Interfaces, grain boundaries, and dislocations are known to have significant impact on the transport properties of materials. Even so, it is still not clear how the structure of interfaces influences the mobility and concentration of carriers that are responsible for transport. Using low angle twist grain boundaries in MgO as a model system, we examine the structural and kinetic properties of vacancies. These boundaries are characterized by a network of screw dislocations. Vacancies of both types, Mg and O, are strongly attracted to the dislocation network, residing preferentially at the misfit dislocation intersections (MDIs). However, the vacancies can lower their energy by splitting into two parts, which then repel each other along the dislocation line between two MDIs, further lowering their energy. This dissociated structure has important consequences for transport, as the free energy of the dissociated vacancies decreases with decreasing twist angle, leading to an increase in the net migration barrier for diffusion as revealed by molecular dynamics simulations. Similar behavior is observed in BaO and NaCl, highlighting the generality of the behavior. Finally, we analyze the structure of the dissociated vacancies as a pair of jogs on the dislocation and construct a model containing electrostatic and elastic contributions that qualitatively describe the energetics of the dissociated vacancy. Our results represent the first validation of a mechanism for vacancy dissociation on screw dislocations in ionic materials first discussed by Thomson and Balluffi in 1962.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Demonstration of finite element simulations in MOOSE using crystallographic models of irradiation hardening and plastic deformation

This report describes the implementation of a crystal plasticity framework (VPSC) for irradiation hardening and plastic deformation in the finite element code, MOOSE. Constitutive models for irradiation hardening and the crystal plasticity framework are described in a previous report [1]. Here we describe these models briefly and then describe an algorithm for interfacing VPSC with finite elements. Example applications of tensile deformation of a dog bone specimen and a 3D pre-irradiated bar specimen performed using MOOSE are demonstrated.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

A defect density-based constitutive crystal plasticity framework for modeling the plastic deformation of Fe-Cr-Al cladding alloys subsequent to irradiation

It is essential to understand the deformation behavior of these Fe-Cr-Al alloys, in order to be able to develop models for predicting their mechanical response under varied loading conditions. Interaction of dislocations with the radiation-induced defects governs the crystallographic deformation mechanisms. A crystal plasticity framework is employed to model these mechanisms in Fe-Cr-Al alloys. This work builds on a previously developed defect density-based crystal plasticity model for bcc metals and alloys, with necessary modifications made to account for the defect substructure observed in Fe-Cr-Al alloys. The model is implemented in a Visco-Plastic Self Consistent (VPSC) framework, to predict the mechanical behavior under quasi-static loading.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Modeling radiation induced segregation in Iron-Chromium alloys

Radiation induced segregation in ferritic Fe-Cr alloys is studied by Atomistic Kinetic Monte Carlo simulations that include di usion of chemical species by vacancy and interstitial migration, recombination, and elimination at sinks. The parameters of the di usion model are tted to DFT calculations. Transport coe cients that control the coupling between di usion of defects and chemical species are measured in dilute and concentrated alloys. Radiation induced segregation near grain boundaries is directly simulated with this model. We nd that the di usion of vacancies toward sinks leads to a Cr depletion. Meanwhile, the di usion of self-interstitials causes an enrichment of Cr in the vicinity of sinks. For concentrations lower than 15%Cr, we predict that sinks will be enriched with Cr for temperatures lower than a threshold. When the temperature is above this threshold value, the sinks will be depleted in Cr. These results are compared to previous experimental studies and models. Cases of radiation induced precipitation and radiation accelerated precipitation are considered.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2015

Slides summary for ExtremeMat project

These slides are part of the final report of the Project s14-ExtremeMat, an Institutional Computing project giving us access to LANL’s computers for the CMIME EFRC computational work

36 MATERIALS SCIENCE↗