Ultrahard and super-stable pure aluminum with Schwarz crystal structure

Figures & data

Figure 1. Microstructural characterization of the as-prepared SC-6 sample. (a) Representative high-resolution TEM image showing individual nanograins outlined by dashed white lines and corresponding SAED pattern (inserted). (b) Grain size distribution of the as-prepared sample. (c) A typical high-resolution HADDF-STEM image of the Schwarz crystal containing five grains. Orange dashed lines represent {111} planes and orange solid lines show coherent twin boundaries (CTBs). (d) Atomic resolution HAADF-STEM D-SC morphology. (e) Atomic resolution HAADF-STEM image of a tiny grain with a CTB with the beam direction along the [110] zone axis. Missing atoms at several corners are indicated by yellow circles.

Figure 2. Yield strength (Hv/3) as a function of initial average grain size in pure Al. Literatures data [6,13,25,26,30–40] are included for pure Al with purity above 99.5 processed via various plastic deformation techniques including cold rolling (CR), accumulative roll-bonding (ARB), multi-axil compression (MAC), high-pressure torsion (HPT), equal channel angle pressing (ECAP), constrained groove pressing (CGP), dynamic plastic deformation (DPD) and surface mechanical grinding treatment (SMGT). The gray dash line is a Hall–Petch plot for pure Al.

Figure 3. Thermal stability of micro-hardness and grain size. (a) Grain size and micro-hardness variations as a function of annealing temperature (with a duration of 1 h) for three samples with initial average grain sizes of 460, 38, and 6 nm, respectively. Microstructural characterization of the as-annealed SC-6 sample. (b) Bright-field TEM image. (c) The grain size distribution. (d) A typical high-resolution HAADF-STEM image of the Schwarz crystal containing four grains. Orange dashed lines represent {111} planes and orange solid lines show coherent CTBs. (e) Atomic resolution HAADF-STEM image of a tiny grain with a twin-free grain with the beam direction along the [110] zone axis. Missing atoms at several corners are indicated by yellow circles.

Figure 4. Ultrahigh thermal stability. Grain coarsening temperature (T_GC) as a function of initial average grain size in pure Al. Literatures data [6,30,34–36,38–40] are included for pure Al with purity above 99.5 processed via various plastic deformation techniques including cold rolling (CR), accumulative roll-bonding (ARB), multi-axil compression (MAC), high-pressure torsion (HPT) and equal channel angle pressing (ECAP).

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