Highlights • An (α-Mg+I-phase) nano-eutectic was discovered in the semisolid Mg-6Zn-1Y alloy under water-cooling conditions. • The spacing of the nano-eutectic is 0.086 (±0.007 ± 0.007 ) μm. • The icosahedral type of I-phase solidified at fast cooling rate is primitive. Abstract The microstructures of Mg–6Zn–1Y (at%) alloys cooling in the 20 °C water and 20 °C air respectively from semisolid state at 540 °C were investigated in this work. An (α-Mg+I-phase) nano-eutectic was discovered in the water-cooled samples. The details of the nano-eutectic were investigated under TEM. Compared with the face-centered icosahedral I-phase solidified at slow cooling rate, the icosahedral type of I-phase solidified at fast cooling rate is primitive. The orientation relationship of the two phase in the nano-eutectic was also studied, namely { 01 1 ̅ 1 ̅ } Mg ∥ { τ 10 } I − phase and { 10 1 ̅ 0 } Mg ∥ 2 f I − phase . The two phases with different lattice structure matched as semi-coherent, which indicated that the interface was in a low energy state.
Leinartas, Konstantinas
Juzeliūnas, Eimutis
Stai?iūnas, Laurynas
Grigucevi?ien?, Asta
Mie?inskas, Povilas
Vai?iūnien?, Jūrat?
Jasulaitien?, Vitalija
Kondrotas, Rokas
Ju?k?nas, Remigijus
Highlights • Mg–Nb alloy films were produced in a wide range of Nb concentrations. • The alloys are promising for in vivo applications. • Passivity was reached in a balanced salt solution when Nb/Mg atomic ratio was one quarter. • A distinctive Nb-enriched network was found within the alloys. Abstract Mg–Nb alloy films have been formed in a wide range of Nb concentrations using the magnetron sputtering technique. The systems are of interest in biomedical applications in-vivo. A distinctive distribution of Nb over Mg matrix was determined by scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. Corrosion behaviour was studied in a balanced salt solution with a physiological pH. Experiments were performed by solution analysis, dc-voltammetry, quartz crystal microgravimetry, X-ray photoelectron spectroscopy and electron microscopy. Quasi-passivity was reached at Nb/Mg atomic concentration ratio of one quarter. It has been shown that corrosion activity could be adjusted according to biomedical requirements by varying Nb concentration.
The mechanism of copper (II) oxide and molybdenum (VI) oxide co-reduction by Mg + C mixture was investigated at non-isothermal conditions by carrying out simultaneous differential thermal (DTA) and thermogravimetric (TG) analyses combined with X-ray diffraction (XRD) analysis of intermediate and final products. The whole process was found to involve several phenomena: interaction between oxides with CuMoO4 salt formation, high-exothermic reactions occurring directly between metal oxides and magnesium, as well as low-exothermic carbothermal reactions. In order to better understand the complex nature of calorimetric and TG curves, the behaviour of each single reagent as well as that of binary, ternary and quaternary mixtures was studied at linear heating. It was revealed that the simultaneous reduction of Cu and Mo oxides proceeds more easily by carbon than by magnesium. Only due to the decisive role of carbon on the reaction pathway, the combined and complete reduction of oxides by Mg/C reducing mixture becomes possible at relatively low temperatures. The sequence of chemical reactions possibly occurring during the heating process on the basis of DTA/TG curves and XRD analyses results of quenched reaction products has been proposed.
Hu, Xiaoyu
Fu, Penghuai
StJohn, David
Peng, Liming
Sun, Ming
Zhang, Mingxing
Highlights • The Mg–3Al alloy was significantly coarsened by the addition of 0.7 wt. % Sm, but dramatically refined by 2.1 wt. % Sm. • Sm coarsened the Mg–3Al alloy by inhibiting the Al–Fe–C–O particles nucleant potency. • 2.1% Sm refined the Mg–3Al alloy because of the solidification of Al2Sm particles. • “Interdependence Theory” was applied to describe the nucleant selection process in the Mg–3Al–2.1Sm alloy. Abstract The effect of Sm on the microstructure of a Mg–3Al alloy has been investigated where it was found that the size of the primary α-Mg grains was significantly coarsened by the addition of 0.7 wt. % Sm, but dramatically refined by 2.1 wt. % Sm. It is proposed that the coarsening effect of Sm is due to a decrease in the nucleation potency of the native Al–Fe–C–O particles when they transform to the lower potency Al–Fe–Sm–C–O particles. The grain refinement observed when 2.1 wt. % Sm is added, is caused by the formation of potent Al2Sm nucleant particles prior to the solidification of α-Mg. The “Interdependence Theory” was then applied to describe the nucleant selection process in the Mg–3Al–2.1Sm alloy.
Tsarkov, Andrey A.
Zanaeva, Erzhena N.
Churyumov, Alexander Yu.
Ketov, Sergey V.
Louzguine-Luzgin, Dmitri V.
Highlights • New alloy compositions based on Mg–Cu–Yb system were developed and investigated. • Increasing content of Ag and Ca leads to improving GFA. • Bulk samples with a composite glassy-crystalline structure were obtained. • Thermodynamic database for Mg–Cu–Yb–Ca–Ag system was created. Abstract The paper presents research into a Mg–Cu–Yb system based metallic glassy alloys. Metallic glasses were prepared using induction melting and further injection on a spinning copper wheel. The effect of alloying by Ag and Ca on the glass forming ability and the kinetics of crystallization of Mg–Cu–Yb system based alloys were studied. The differential scanning calorimeter and X-ray diffractometer were used to investigate the kinetics of crystallization and the phase composition of the samples. An indicator of glass forming ability, effective activation energy of crystallization, and enthalpy of mixing were calculated. An increase of the Ca and Ag content has a positive effect on the glass forming ability, the effective activation energy of crystallization, and the enthalpy of mixing. The highest indicators of the glass forming ability and the thermal stability were found for alloys that contain both alloying elements. The Ag addition suppresses precipitation of the Mg2Cu phase during crystallization. A dual-phase glassy-nanocrystalline Mg structure was obtained in Mg65Cu25Yb10 and Mg59.5Cu22.9Yb11Ag6.6 alloys after annealing. Bulk samples with a composite glassy-crystalline structure were obtained in Mg59.5Cu22.9Yb11Ag6.6 and Mg64Cu21Yb9.5Ag5.5 alloys. A thermodynamic database for the Mg–Cu–Yb–Ca–Ag system was created to compare the process of crystallization of alloys with polythermal sections of the Mg–Cu–Yb–Ca–Ag phase diagram. Graphical abstract