The LPSO Structure with an Extra Order beyond Stacking Periodicity

Abstract

We have investigated a novel long-period stacking/order (LPSO) structure in a Mg 75 Al 10 Y 15 alloy, based on electron diffraction, scanning transmission electron microscopy (STEM) observations and first-principles calculations. Fundamental lattice of the present LPSO structure is identified as one of the stacking polytypes of 10H-type, and the in-plane 6©ð1 210Þ hcp superlattice order is well developed as represented by the L1 2-type Al 6 Y 8 cluster arrangement. We find that, across the stacking direction, the inter-cluster order tends to be further developed beyond its periodicity, showing an extra order which doubles the 10H-stacking periodicity. We have constructed the LPSO variant models including such extra inter-cluster order, and their formation energy comparison has confirmed that the extra order becomes indeed stable when the L1 2-Al 6 Y 8 cluster contains interstitial atoms. The interstitial effects turn out to be prominent in favor of Y atom, as being consistent with the STEM observations.

Microstructure and Its Evolution of Solute-Enriched Stacking Faults in Kink-Deformed Mg₉₇Zn₁Y₂

“…This exceptional mechanical performance is believed to be associated with the unique kink deformation promoted by the presence of the long-period stacking order (LPSO) structure in Mg-TM-RE alloys. [1][2][3][4][5][6] In addition to the LPSO structure, solute-enriched stacking faults (SESFs), which have a face-centered cubic stacking, also exist in the hexagonal close-packed α-Mg matrix. The distribution of such LPSO and SESFs forms microstructural variations in the α-Mg matrix.…”

Local Structural Analysis around Solute-Element in Annealed Mg_99.2Zn_0.2Y_0.6 Alloy Using X-ray Fluorescence Holography

“…A series of Mg alloys containing a few atomic percent of transition metal (TM) and rare-earth (RE) has been gathering much attention because of its excellent mechanical properties, such as very large tensile yield strength of ~600 MPa [1][2][3] . Furthermore, these alloys exhibit a curious atomic-level structure, the so-called synchronized long period stacking ordered (LPSO) structure [4][5][6][7][8][9][10][11][12][13][14][15] , where the solute TM and RE elements are aggregated at the periodically inserted fcc-type stacking faults.…”

The γ” Phase in Mg-RE-TM Alloys: A Review on the Structure and Stability of the γ” Phase and Its Effect on Mechanical Properties

“…are micro-alloyed together with the RE elements to constitute different strengthening phases. The main strengthening phases in Mg-RE-TM alloys include prismatic β series precipitates [3][4][5][6] and basal-plate-like precipitates that include the γ' [7,8]/long-period stacking ordered (LPSO) phase [9][10][11][12][13] and γ" phases [7,[14][15][16][17]. These strengthening phases play a critical role in determining the mechanical properties of these alloys [18].…”