Concentrated Solid Solution Alloys Research Articles

Suppression of vacancy cluster growth in concentrated solid solution alloys

Large vacancy clusters, such as stacking-fault tetrahedra, are detrimental vacancy-type defects in ion-irradiated structural alloys. Suppression of vacancy cluster formation and growth is highly desirable to improve the irradiation tolerance of these materials. In this work, we demonstrate that vacancy cluster growth can be inhibited in concentrated solid solution alloys by modifying cluster migration pathways and diffusion kinetics. The alloying effects of Fe and Cr on the migration of vacancy clusters in Ni concentrated alloys are investigated by molecular dynamics simulations and ion irradiation experiment. While the diffusion coefficients of small vacancy clusters in Ni-based binary and ternary solid solution alloys are higher than in pure Ni, they become lower for large clusters. This observation suggests that large clusters can easily migrate and grow to very large sizes in pure Ni. In contrast, cluster growth is suppressed in solid solution alloys owing to the limited mobility of large vacancy clusters. The differences in cluster sizes and mobilities in Ni and in solid solution alloys are consistent with the results from ion irradiation experiments.

Enhanced damage resistance and novel defect structure of CrFeCoNi under in situ electron irradiation

Defect production and growth in CrFeCoNi, a single-phase concentrated solid solution alloy, is characterized using in situ electron irradiation inside a transmission electron microscope operated at 400–1250kV and 400°C. All observed defects are interstitial-type, either elliptical Frank loops or polygonal (mostly rhombus) perfect loops. Both forms of loops in CrFeCoNi exhibit a sublinear power law of growth that is >40 times slower than the linear defect growth in pure Ni. This result shows how compositional complexity impacts the production of Frenkel pairs and the agglomeration of interstitials into loops, and, thus, enhances the radiation tolerance.

Microstructural stability and mechanical behavior of FeNiMnCr high entropy alloy under ion irradiation

In recent years, high entropy alloys (HEAs) have attracted significant attention due to their excellent mechanical properties and good corrosion resistance, making them potential candidates for high temperature fission and fusion structural applications. However there is very little known about their radiation resistance, particularly at elevated temperatures relevant for energy applications. In the present study, a single phase (face centered cubic) concentrated solid solution alloy of composition 27%Fe-28%Ni-27%Mn-18%Cr was irradiated with 3 or 5.8 MeV Ni ions at temperatures ranging from room temperature to 700 °C and midrange doses from 0.03 to 10 displacements per atom (dpa). Transmission electron microscopy (TEM), scanning transmission electron microscopy with energy dispersive x-ray spectrometry (STEM/EDS) and X-ray diffraction (XRD) were used to characterize the radiation defects and microstructural changes. Irradiation at higher temperatures showed evidence of relatively sluggish solute diffusion with limited solute depletion or enrichment at grain boundaries. The main microstructural feature at all temperatures was high-density small dislocation loops. Voids were not observed at any irradiation condition. Nano-indentation tests on specimens irradiated at room temperature showed a rapid increase in hardness ∼35% and ∼80% higher than the unirradiated value at 0.03 and 0.3 dpa midrange doses, respectively. The irradiation-induced hardening was less pronounced for 500 °C irradiations (<20% increase after 3 dpa). Overall, the examined HEA material exhibits superior radiation resistance compared to conventional single phase Fe-Cr-Ni austenitic alloys such as stainless steels. The present study provides insight on the fundamental irradiation behavior of a single phase HEA material over a broad range of irradiation temperatures.

Damage accumulation in ion-irradiated Ni-based concentrated solid-solution alloys

Irradiation-induced damage accumulation in Ni0.8Fe0.2 and Ni0.8Cr0.2 alloys are investigated using molecular dynamics (MD) simulations to assess possible enhanced radiation-resistance in these face-centered cubic (fcc), single-phase, concentrated solid-solution alloys, as compared with pure fcc Ni. The Ni0.8Cr0.2 and Ni0.8Fe0.2 alloys demonstrate higher radiation resistance compared to Ni. The total number of point defects produced in Ni0.8Cr0.2 and Ni0.8Fe0.2 is approximately 2.5 and 1.4 times lower than in Ni, respectively, due to efficient defect recombination in the chemically disordered alloys. Both interstitial and vacancy clusters are formed in all three materials. In Ni, large interstitial clusters are produced; whereas in Ni0.8Cr0.2, smaller interstitial clusters are produced but with a higher number. This indicates a higher mobility of interstitials in Ni compared to Ni0.8Cr0.2. Moreover, Ni0.8Cr0.2 shows better radiation resistance than Ni0.8Fe0.2. Larger interstitial clusters and 1.7 times higher numbers of accumulated point defects are observed in Ni0.8Fe0.2, in comparison with Ni0.8Cr0.2. Due to the low mobility of vacancies on the MD time scales, they are found primarily as single point defects and small clusters in all materials. While performance improvement is observed in the alloys, the difference in irradiation response between Ni0.8Cr0.2 and Ni0.8Fe0.2 indicates the importance of element choice to achieve the desired property.

Influence of chemical disorder on energy dissipation and defect evolution in concentrated solid solution alloys.

A grand challenge in materials research is to understand complex electronic correlation and non-equilibrium atomic interactions, and how such intrinsic properties and dynamic processes affect energy transfer and defect evolution in irradiated materials. Here we report that chemical disorder, with an increasing number of principal elements and/or altered concentrations of specific elements, in single-phase concentrated solid solution alloys can lead to substantial reduction in electron mean free path and orders of magnitude decrease in electrical and thermal conductivity. The subsequently slow energy dissipation affects defect dynamics at the early stages, and consequentially may result in less deleterious defects. Suppressed damage accumulation with increasing chemical disorder from pure nickel to binary and to more complex quaternary solid solutions is observed. Understanding and controlling energy dissipation and defect dynamics by altering alloy complexity may pave the way for new design principles of radiation-tolerant structural alloys for energy applications.