Radiation-resistant aluminium alloy for space missions in the extreme environment of the solar system

Abstract

Future human-based exploration of our solar system requires the invention of materials that can resist harsh environments. Age-hardenable aluminium alloys would be attractive candidates for structural components in long-distance spacecrafts, but their radiation resistance to solar energetic particles is insufficient. Common hardening phases dissolve and displacement damage occurs in the alloy matrix, which strongly degrades properties. Here we present an alloy where hardening is achieved by T-phase, featuring a giant unit cell and highly-negative enthalpy of formation. The phase shows record radiation survivability and can stabilize an ultrafine-grained structure upon temperature and radiation in the alloy, therby successfully preventing displacement damage to occur. Such concept can be considered ideal for the next-generation space materials and the design of radiation resistant alloy.

Figures (6)

• Figure 1: Synthesis of the UFG aluminium crossover alloy | A. To achieve an UFG microstructure from the bulk AlMgZnCuAg crossover alloy, the technique of HPT was used. B. After processing, BFTEM revealed a UFG microstructure. Local nanochemistry analysis revealed segregation of all alloying elements to the grain boundaries, but no T-phase precipitates in the as-processed condition as shown in the STEM-EDX mapping in C.
• Figure 2: Alloy's stability under irradiation | Nucleation of T-phase precipitates in the UFG AlMgZnCuAg crossover alloy was observed after heat-treatment using a ramp of 10 K$\cdot$min$^{-1}$ up to 506 K A. The microstructural evolution of the UFG AlMgZnCuAg crossover alloy as monitored in situ within the TEM is shown in the set of underfocused BFTEM micrographs in B from 0 to 100 dpa. The alloy's microstructure neither exhibit formation of dislocation loops nor grain growth at a maximum dose of 100 dpa. Voids are only observed to form at around 75 dpa.
• Figure 3: Alloy's stability under irradiation (post-irradiation examination) | Post-irradiation methodologies using conventional and analytical electron-microscopy were used to investigate the origins of the alloy's stability under irradiation. A STEM-EDX mapping and B-D SAED, HRTEM and FFT, respectively, show that T-phase precipitates are stable and did not dissolve at the exemplary dose of 6 dpa, which is six tunes2020prototypic and thirty lohmann1987microstructure times higher dose than previous reports on irradiation-assisted dissolution of hardening phases in bulk Al-based alloys. The schematics in E exhibit microstructural differences in the UFG alloy before and after a heat treatment, establishing a new alloy design strategy to achieve high radiation tolerance. T-phase precipitates are prone to nucleate, grow and stabilize the structure.
• Figure 4: Radiation Survivability Level of T-phase precipitates and thermodynamic origins of their high radiation tolerance | A survey using STEM-EDX mapping in the post-irradiated specimens shows that T-phase precipitates surviving up to a dose of 24 dpa, as denoted in A. After 24 dpa, the precipitates began to (progressively) dissolve and at the dose of 100 dpa, B, no T-phase precipitates were detected in the UFG AlMgZnCuAg crossover alloy. Radiation-induced precipitation of pure Ag nanoprecipitates is noted again at doses around 100 dpa. Thermodynamic calculations in plot C show that the entalphy of formation for T-phase precipitates is significantly lower compared with hardening precipitates within the existing Al-based alloys. The T-phase is found to be stable over a wide range of chemical ratios as shown in the ternary equilibrium phase diagram in D calculated at both 298 K and 1 bar. E The crystal structures of the (Al$_{2}$Cu) $\theta$-phase, (Mg$_{2}$Zn) $\eta$-phase, (Mg$_{2}$Si) $\beta$-phase and (Mg$_{32}$(Zn,Al)$_{49}$) demonstrate that chemical complexity is a distinct characteristic of the T-phase precipitates tailoring the radiation resistance of the UFG AlMgZnCuAg crossover alloy.
• Figure 5: Irradiation experiments carried out on the UFG-crossover sample | The experiments were carried out up to 100 dpa. The Radiation Survivability Level of the T-phase was determined to be at 24 dpa. The experiments were carried out further up to 100 dpa. The UFG-microstructure was still intact after 100 dpa.