Formation of β' phase in LPSO structures in an Mg88Co5Y7 alloy

Formation of β’ phase in long-period stacking ordered(LPSO) structures in an Mg;Co;Y;(at.%) alloy after aging at 200 °C for 24 h or electron beam(EB) irradiation has been studied by high-angle annular dark-field scanning transmission electron microscopy(HAADFSTEM). β’ phase was precipitated only in the Mg matrix but not in LPSO structures after aging at 200 °C for 24 h. LPSO structure containing stacking defects transforms into the β’-long phase during EB irradiation, which plays a key role in accelerating solute atoms’ diffusion. New complex β’(LPSO) structures formed in the alloy after EB irradiation, such as β’(12 H) structure with an orthorhombic lattice(Mg;Y, Cmcm,a = 2 _(a0)= 0.642 nm, b=4√3_(a0), c = 6 _(c0)= 3.12 nm).

Microstructure development and biodegradation behavior of additively manufactured Mg-Zn-Gd alloy with LPSO structure

Biodegradable magnesium(Mg)alloy has been considered as a new generation of orthopedic implant ma-terial.Nevertheless,local corrosion usually occurs since the severe micro-galvanic behavior amongα-Mg and precipitates,and results in too rapid degradation.In this study,porous Mg-Zn-Gd part was fabricated using laser additive manufacturing combined with solution heat treatment.During heat treatment,the precipitatedβ-(Mg,Zn)_(3) Gd phase dissolved inα-Mg,and reduced the energy threshold of stacking faults on basal planes,which finally triggered the formation of long period stacking ordered(LPSO)phase.The LPSO phases owned minor potential difference withα-Mg,thus causing less micro-galvanic corrosion ten-dency as compared toβ-(Mg,Zn)_(3) Gd phase.More importantly,they were uniformly distributed within theα-Mg grains and showed different orientations between adjacent grains.As a result,the LPSO-reinforced Mg-Zn-Gd tended to expand laterally during corrosion evolution,and achieved uniform degradation with a considerably reduced degradation rate of 0.34 mm/year.Moreover,in-vitro cell tests further proved its favorable biocompatibility.This work highlighted the additively manufactured Mg-Zn-Gd with LPSO structure showed great potential for orthopedic application.

Developing new Mg alloy as potential bone repair material via constructing weak anode nano-lamellar structure

The mechanics-corrosion and strength-ductility tradeoffs of magnesium(Mg)alloys have limited their applications in fields such as orthopedic implants.Herein,a fine-grain structure consisting of weak anodic nano-lamellar solute-enriched stacking faults(SESFs)with the average thickness of 8 nm and spacing of 16 nm is constructed in an as-extruded Mg96.9Y1.2Ho1.2Zn0.6Zr0.1(at.%)alloy,obtaining a high yield strength(YS)of 370 MPa,an excellent elongation(EL)of 17%,and a low corrosion rate of 0.30 mm y−1(close to that of high-pure Mg)in a uniform corrosion mode.Through scanning Kelvin probe force microscopy(SKPFM),one-dimensional nanostructured SESFs are identified as the weak anode(∼24 mV)for the first time.The excellent corrosion resistance is mainly related to the weak anodic nature of SESFs and their nano-lamellar structure,leading to the more uniform potential distribution to weaken galvanic corrosion and the release of abundant Y^(3+)/Ho^(3+)from SESFs to form a more protective film with an outer Ca_(10)(PO_(4))_(6)(OH)_(2)/Y_(2)O_(3)/Ho_(2)O_(3) layer(thickness percentage of this layer:72.45%).For comparison,the as-cast alloy containing block 18R long period stacking ordered(LPSO)phase and the heat-treated alloy with fine lamellar 18R-LPSO phase(thickness:80 nm,spacing:120 nm)are also studied,and the characteristics of SESFs and 18R-LPSO phase,such as the weak anode nature of the former and the cathode nature of the latter(37-90 mV),are distinguished under the same alloy composition.Ultimately,we put forward the idea of designing Mg alloys with high mechanical and anti-corrosion properties by constructing"homogeneous potential strengthening microstructure",such as the weak anode nano-lamellar SESFs structure.

Friction and wear behavior of Mg–11Y–5Gd–2Zn–0.5Zr(wt%)alloy with oil lubricant

The sliding friction and wear behaviors of Mg-11Y-5Gd-2Zn-0.5Zr （wt%） alloy were investigated under oil lubricant condition by pin-on-disk configuration with a constant sliding distance of 1,000 m in the temperature range of 25-200℃. Results indicate that the volumetric wear rates and average friction coefficients decrease with the increase of sliding speeds, and increase with the increase of test temperature below 150℃. The hard and thermally stable Mg12（Y,Gd）Zn phase with long-period stacking order structure in the alloy presents significant wear resistance, The wear mechanism below 100℃ is abrasive wear as a result of plastic extrusion deformation. The corporate effects of severe abrasive, oxidative, and delaminating wear result in the tribological mechanism above 100℃.

Corrosion Behavior of Mg-Zn-Y Alloy with Long-period Stacking Ordered Structures

Mg-Zn-Y alloys with long-period stacking ordered structures were prepared by an ingot casting method. The corrosion performance of Mg-Zn-Y alloys was studied by combining gas-collecting test, immersion test and electrochemical measurements in order to determine the corrosion rate and mechanism of the alloys. The results showed that the volume fraction of Mg（12）YZn phase increased and the shape of the Mg（12）YZn phase changed from discontinuous to continuous net-like with increasing Zn and Y content. The corrosion rate of the alloys greatly depended on the distribution and volume fraction of the Mg（12）YZn phase. Corrosion products appeared at the junction of Mg phase and Mg（12）YZn phase, indicating that the Mg（12）YZn phase accelerated galvanic corrosion of Mg matrix. Mg（97）Zn1Y2 alloy shows the lowest corrosion rate due to the continuous distribution of Mg（12）YZn phase.