Atomic-level heterogeneity and defect dynamics in concentrated solid-solution alloys

Abstract

Performance enhancement of structural materials in extreme radiation environments has been actively investigated for many decades. Traditional alloys, such as steel, brass and aluminum alloys, normally contain one or two principal element(s) with a low concentration of other elementals. While these exist in either a mixture of metallic phases (multiple phases) or solid solution (single phase), limited or localized chemical disorder is a common characteristic of the main matrix. In sharp contrast to the traditional alloys, recently developed single-phase concentrated solid so lution alloys (CSAs) contain multiple elemental species in equiatomic or high concentrations with different elements randomly arranged on a crystalline lattice. Due to the lack of elemental predictability in these CSAs, they exhibit significant chemical disorders and unique site-to-site lattice distortions. While it has long been recognized that specific compositions of traditional alloys have enhanced radiation resistance, it remains unclear how the atomic-level heterogeneity affects defect formation, damage accumulation, and microstructural evolution. Such knowledge gaps have been a roadblock to future-generation energy technology. CSAs with a simple crystal structure, but complex chemical disorder are ideal systems to understand how compositional complexity influences defect dynamics, and to fill the knowledge gaps with focus on electronic-and atomic-level interactions, mass and energy transfer processes, and radiation resistance performance. Recent advances of defect dynamics and irradiation performance of CSAs are reviewed, intrinsic chemical effects on radiation performance are discussed, and future directions are suggested.

Single-Phase Concentrated Solid-Solution Alloys: Bridging Intrinsic Transport Properties and Irradiation Resistance

“…The physics picture has been intuitively described as follows: the reduced thermal conductivity can slow down the dissipation of the deposited heat, lengthen the thermal spike, which enhances the lifetime of thermally enhanced recombination stage Zhang Y. et al, 2017). Experimental support of this hypothesis has been seen from the correlation between thermal conductivity and damage level of the Ni-containing equiatomic SP-CSAs under low dose room temperature irradiations (e.g., comparing Figures 2, 6a).…”

“…First, it has been considered to reduce of surviving defects in SP-CSAs under room and low temperature irradiations, by reducing the separation of interstitial and vacancy populations, enhancing the their interactions, and further promoting the defect recombination (Velişa et al, 2017b;Zhang Y. et al, 2017). Second, this mechanism has been considered to attribute to the qualitative different void distribution and the reduced swelling in SPCSAs (see Figures 7a,b): Interstitials migrate fast in Ni and NiCo, leaving the vacancies behind in the matrix oversaturated and aggregated into large voids.…”

“…In addition, interesting electrical transport properties such as superconductivity (Koželj et al, 2014) and quantum critical behavior (Sales et al, 2016(Sales et al, , 2017 have been discovered, and the HEAs have been considered promising in functional applications such as thermoelectric materials (Shafeie et al, 2015;Fan et al, 2016) and soft ferromagnetic materials (Zhang et al, 2013). Furthermore, recent studies have linked the mass and energy transport properties to the enhanced irradiation resistance (Zhang et al, 2015;Lu et al, 2016b;Zhang Y. et al, 2017). Different from the traditional design strategies of irradiation tolerant alloys that usually introduce extrinsic defect sinks, such as grain boundary, secondary phases, and nano particles (Ukai and Fujiwara, 2002;Was, 2007;Garner, 2012), HEAs allow the focus on the effects of intrinsic properties determined by the major alloying elements on irradiation response, as considered a new path of designing radiation resistant alloys.…”

Local lattice distortion in high-entropy alloys

“…These local deviations of structure change the nature of short range interactions and subsequently strongly influence the resultant properties of the material. Expanding our scientific knowledge of atomic-level heterogeneity from the relative simplicity of ideal, perfectly ordered, or structurally averaged materials to real materials should give rise to properties that meet the challenges at the frontiers of matter and energy [2][3][4] . When it comes to a new class of structural materials, compositionally complex HEAs, enthalpy among each atomic pair and size mismatch are not the only decisive factors to form single-phase concentrated solid solution alloys (SP-CSAs) but also short-range interactions to determine local chemical (i.e.…”

“…On the other hand, undersized or oversized solute has been alloyed to austenitic or ferritic steels to suppress radiation-induced segregation at grain boundaries and void swelling by trapping point defects 4,[16][17][18][19][20] . Moreover, large lattice distortions can retard dislocation movement to suppress the growth of damage structures 10,21 .…”