Anisotropic Plastic Behavior in an Extruded Long-Period Ordered Structure Mg90Y6.5Ni3.5 (at.%) Alloy

Gerardo Garces,Andreas Stark,Norbert Schell,Rafael Barea

doi:10.3390/cryst10040279

Gerardo Garces, Andreas Stark + Show 2 more

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https://doi.org/10.3390/cryst10040279

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Journal: Crystals	Publication Date: Apr 7, 2020
Citations: 4	License type: CC BY 4.0

Affiliation: Helmholtz-Zentrum Hereon, Nebrija University

Abstract

The Mg90Y6.5Ni3.5 alloy composed almost completely of the Long-Period-Stacking-Ordered (LPSO) phase has been prepared by casting and extrusion at high temperature. An elongated microstructure is obtained where the LPSO phase with 18R crystal structure is oriented with its basal plane parallel to the extrusion direction. Islands of α-magnesium are located between the LPSO grains. The mechanical properties of the alloy are highly anisotropic and depend on the stress sign as well as the relative orientation between the stress and the extrusion axes. The alloy is stronger when it is compressed along the extrusion direction. Under this configuration, the slip of <a> dislocations in the basal plane is highly limited. However, the activation of kinking induces an increase in the plastic deformation. In the transversal extrusion direction, some grains deform by the activation of basal slip. The difference in the yield stress between the different stress configurations decreases with the increase in the test temperature. The evolution of internal strains obtained during in-situ compressive experiments reveals that tensile twinning is not activated in the LPSO phase.

Highlights

Mg-Transition metal (TM: Zn, Ni, Cu, Co and Al)-Rare Earth (RE: Y, Gd, Dy, Ho, Er, etc.) alloys with a Long-Period Stacking Ordered (LPSO) crystal structure have attracted great attention due to their high mechanical strength, which is maintained up to 300 ◦ C
The present study examines the orientation dependence of strength of an extruded Mg90 Y6.5 Ni3.5 alloy with an almost fully LPSO phase and its temperature dependences
The 3D microstructure of the extruded material, shown in Figure 1a, was characterized by the presence of two phases, which are elongated along the extrusion direction

Summary

Introduction

Mg-Transition metal (TM: Zn, Ni, Cu, Co and Al)-Rare Earth (RE: Y, Gd, Dy, Ho, Er, etc.) alloys with a Long-Period Stacking Ordered (LPSO) crystal structure have attracted great attention due to their high mechanical strength (around 600 MPa), which is maintained up to 300 ◦ C. The LPSO phases are typically Mg-TM-RE compounds whose structure show a long range stacking of basal, hexagonal planes with periodic enrichment of TM and RE atoms in basal planes [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. The LPSO phase with 18R or 14H structure shows a strong elastic and plastic anisotropy. The LPSO phase exhibits a higher Young’s modulus and shear modulus compared to Mg [19,20,21,22]

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