Yajun Xue

Microstructure and biocorrosion behaviors of solution treated and as-extruded Mg–2.2Nd–xSr–0.3Zr alloys

Abstract Mg–2.2Nd– x Sr–0.3Zr alloys ( x =0, 0.4 and 0.7, mass fraction, %) were prepared by gravity casting. Solution treatment was conducted on the as-cast alloys to homogenize microstructure, and hot extrusion was subsequently conducted. Microstructure was observed using an optical microscope and a scanning electron microscope. Biocorrosion behaviors of the alloy in simulated body fluid were analyzed by mass loss, hydrogen evolution and Tafel polarization experiments. The results show that the amount of residual eutectic phase of the solution treated alloys increases with increasing Sr addition, and the grains are significantly refined after hot extrusion. The corrosion resistance of the solution treated alloys deteriorates apparently with increasing Sr addition, while the corrosion resistance of the as-extruded alloys is improved with Sr addition. Nevertheless, the biocorrosion behavior of the as-extruded alloys obtained by Tafel polarization shows different trends from those obtained by the other two methods.

Effect of heat treatment on microstructure, mechanical properties and in vitro degradation behavior of as-extruded Mg-2.7Nd-0.2Zn-0.4Zr alloy

Abstract Mg-2.7Nd-0.2Zn-0.4Zr (mass fraction, %) alloy was designed for degradable biomedical material. The ingots of the alloy were solution treated and then hot extruded. The extruded rods were heat treated with aging treatment, solution treatment and solution+aging treatment, respectively. Microstructures of the alloy were observed by optical microscopy (OM) and scanning electron microscopy (SEM). Mechanical properties at room temperature were tested. In vitro degradation behavior of the alloy immersed in simulated body fluid was measured by hydrogen evolution and mass loss tests. The degradation morphologies of the alloy with and without degradation products were observed by SEM. The results show that the grains grow apparently after solution treatment. Solution treatment improves the elongation of as-extruded alloy significantly and decreases the strength, while aging treatment improves the strength and reduces the elongation of the alloy. The yield ratio is reduced by heat treatment. The in vitro degradation results of the alloy show that solution treatment on the as-extruded alloy results in a little higher degradation rate and aging treatment on the alloy can reduce degradation rate slightly.

Corrosion properties of stainless steel 316L/Ni–Cu–P coatings in warm acidic solution

Abstract In order to improve corrosion resistance of stainless steel 316L in warm acidic solution, Ni–Cu–P coatings with high copper and phosphorus contents were deposited onto stainless steel 316L substrates via electroless plating. The structure of the film and its resistance to corrosion in a warm acidic environment were investigated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction spectrometry (XRD), polarization curves, electrochemical impedance spectroscopy (EIS), and dipping corrosion tests, respectively. The results demonstrate that Ni–Cu–P coatings consist of two types of nodules, which are 19.98% Cu and 39.17% Cu (mass fraction) respectively. The corrosion resistance of the 316L substrate when subjected to a warm acidic solution is significantly improved by the addition of the new type of the Ni–Cu–P coating. The as-plated coatings demonstrate better corrosion resistance than annealed coatings. As-plated coatings and those annealed at 673 K are found to corrode selectively, while pitting is observed to be the main corrosion mechanism of coatings annealed at 773 and 873 K.

Effect of Gd/Nd ratio on mechanical and biocorrosion properties of as-extruded Mg–Nd–Gd–Sr–Zn–Zr alloys

Abstract Mg–(4–x)Nd–x Gd–0·3Sr–0·2Zn–0·4Zr (wt.-%, x = 0, 1, 2, and 3) alloys with various Gd/Nd ratios were prepared by gravity casting, solution-treated and then hot extruded. The microstructures, mechanical properties at room temperature, corrosion behaviour in simulated body fluid of the as-extruded alloys were studied. The as-extruded alloys undergo partially dynamic recrystallisation, and the equiaxed grains become coarse with increasing Gd/Nd ratio. The strength of the alloys increases first and then decreases with increasing the Gd/Nd ratio; however, the elongation of the alloys increases apparently with increasing Gd/Nd ratio. Both immersion test and polarisation test indicate that the corrosion rate of the as-extruded alloys is reduced with increasing the Gd/Nd ratio, and the alloys exhibit relatively uniform corrosion morphologies.