Liqing Wang

Precipitation behavior of M2N in a high-nitrogen austenitic stainless steel during isothermal aging

The precipitation behavior of M 2 N and the microstructural evolution in a Cr-Mn austenitic stainless steel with a high nitrogen content of 0.43mass% during isothermal aging has been investigated using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The aging treatments have led to the decomposition of nitrogen supersaturated austenitic matrix through discontinuous cellular precipitation. The precipitated cells comprise alternate lamellae of M 2 N precipitate and austenitic matrix. This kind of precipitate morphology is similar to that of pearlite. However, owing to the non-eutectoidic mechanism of the reaction, the growth characteristic of the cellular precipitates is different from that of pearlite in Fe-C binary alloys. M 2 N precipitate in the cell possesses a hexagonal crystal structure with the parameters a = 0.4752nnm and c = 0.4429nm, and the orientation relationship between the M 2 N precipitates and austenite determined from the SADP is [0110] M2N //[101]γ, [2110] M2N //[010]γ,

Self-Assembly of Two Unit Cells into a Nanodomain Structure Containing Five-Fold Symmetry

Five-fold symmetry was forbidden for the periodic crystals until the discovery of the Al-Mn icosahedral quasicrystal. We report a kind of precipitated rod-shaped nanophase containing five-fold symmetry but not belonging to any crystals or quasicrystals discovered so far. These metastable nanodomain phases, which precipitated in Mg-6Zn alloy during isothermal aging at 200 °C, contain two separate unit cells in the 2D plane perpendicular to the five-fold axis but with periodic atom arrangement along the five-fold axis, that is, 72° rhombus structure and 72° equilateral hexagon structure. The self-assembly of two unit cells under some geometrical constraints into a nanodomain contains the 2D five-fold, C14, and C15 structures. This finding confirms the existence of solid matters in a special structure between the crystals and quasicrystals, and it is expected to provide a way to understand the atomic arrangement and stacking behavior in condensed matters.

Effect of solid solution treatment on in vitro degradation rate of as-extruded Mg-Zn-Ag alloys

Abstract The degradation behaviors of the as-extruded and solution treated Mg-3Zn-xAg (x=0, 1, 3, mass fraction, %) alloys, as well as as-extruded pure Mg, have been investigated by immersion tests in simulated body fluid (SBF) at 37 °C. The as-extruded Mg-Zn(-Ag) alloys contained Mg51Zn20 and Ag17Mg54. While the quasi-single phase Mg-Zn(-Ag) alloys were obtained by solution treatment at 400 °C for 8 h. The quasi-single phase Mg-Zn(-Ag) alloys showed lower degradation rate and more homogeneous degradation than corresponding as-extruded Mg alloys. Degradation rate of solid-solution treated Mg-3Zn-1Ag and Mg-3Zn-3Ag was approximately half that of corresponding as-extruded Mg alloy. Moreover, the degradation rate of solid-solution treated Mg-3Zn and Mg-3Zn-1Ag was equivalent to that of as-extruded pure Mg. However, heterogeneous degradation also occurred in quasi-single phase Mg-Zn-Ag alloys, compared to pure Mg. So, preparing complete single-phase Mg alloys could be a potential and feasible way to improve the corrosion resistance.

Isothermal section of Mg-rich corner in Mg–Zn–Al ternary system at 335 °C

Abstract The phase equilibria and compositions at the Mg-rich corner of the Mg–Zn–Al ternary system at 335 °C were systemically investigated through the equilibrated alloy method by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) assisted with energy dispersive spectroscopy of X-ray (EDS). It is experimentally testified that the α -Mg solid solution is not in equilibrium with the Mg 32 (Al, Zn) 49 ( τ ) ternary intermetallic compound or q quasicrystalline phase, but only in equilibrium with one ternary intermetallic compound Al 5 Mg 11 Zn 4 ( φ ). The whole composition range of the φ phase was also obtained at 335 °C, i.e., 52.5%–56.4% Mg, 13.6%–24.0% Al, 19.6%–33.9% Zn (mole fraction). The solubility of Al in the MgZn phase is remarkably more than that in the Mg 7 Zn 3 phase, and the maximum is about 8.6% Al. Aluminum and zinc are simultaneously soluble in the α -Mg solid solution.