Haoran Geng

Complex modification of hypereutectic Al-Si alloy by a new Al-Y-P master alloy

In this article, a novel Al-6Y-2P master alloy with cubic YP particles was successfully synthesized and its complex modification performance on Al-18Si alloy has also been investigated. With the doping of La and Ce, (YxLa1-x)P and (YxCe1-x)P particles still exhibit cubic morphologies in three dimensional spaces (3-D space). The excellent complex modification of Al-18Si alloy can be obtained with the addition of Al-6Y-2P master alloy. Under the optimized conditions, i.e. melting temperature of 780 °C, addition level of 1.5 wt% and holding time of 30–60 min, the tensile strength and Brinell hardness of Al-18Si alloys can be significantly increased by 16.8% and 17.1%, respectively. It is proposed that the Si atoms in the melt could promote the structure evolution of YP to AlP with the release of Y, which would be reason for the excellent composite modification performance of the developed Al-6Y-2P master alloy.

Effects of WO3 Micro/Nano-Inclusions on the Thermoelectric Properties of Co4Sb11.7Te0.3 Skutterudite

In this study, nano-sized WO3 powder was dispersed into Co4Sb1.7Te0.3 thermoelectric matrix by ball milling and hot-press sintering technology. The results of scanning electron microscopy (SEM) showed that the WO3 phase distributed uniformly in the form of inclusions on the matrix. High-resolution transmission electron microscopy (HRTEM) presented that the average size of embedded nano-WO3 was about 50 nm. With the content of WO3 increasing, the electrical conductivity (σ) of Co4Sb11.7Te0.3 decreased and the absolute value of Seebeck coefficient (a) increased. The absolute value of a for 1.5% WO3/Co4Sb11.7Te0.3 composite was 258 µV/K at 650 K. The minimal lattice thermal conductivity (K(L)) of WO3/Co4Sb11.7Te0.3 achieved in the present work was 1.52 W/m K at 650 K. The total thermal conductivity (K) of WO3/Co4Sb11.7Te0.3 composites decreased obviously, which resulted from the phonon scattering by the WO3 inclusions locating on the grain boundaries of Co4Sb11.7Te0.3 matrix. The highest ZTof 0.71 was achieved at 750 K for 1.5%WO3/Co4Sb11.7Te0.3 composite.

Synthesis and thermoelectric properties of tantalum-doped ZrNiSn half-Heusler alloys

The Ta-doped ZrNiSn half-Heusler alloys, Zr1-xTaxNiSn, were synthesized by arc melting and hot-press sintering. Microstructure of Zr1-xTaxNiSn compounds were analyzed and the thermoelectric (TE) properties of Zr1-xTaxNiSn compounds were measured from room temperature to 823 K. The electrical conductivity increased with increasing Ta content. The Seebeck coefficient of Zr1-xTaxNiSn compounds was sharply decreased with increasing Ta content. The Hall mobility was proportional to T-1.5 above 673 K, indicating that the acoustic phonon scattering was predominant in the temperature range. The thermal conductivity was effectively depressed by introducing Ta substitution. The figure of merit of ZrNiSn compounds was improved due to the decreased thermal conductivity and increased electrical conductivity. The maximum ZT value of 0.60 was achieved for Zr0.97Ta0.03NiSn sample at 823 K.

Glass-forming ability, microhardness, corrosion resistance, and dealloying treatment of Mg60−x Cu40Nd x alloy ribbons

The influence of Nd addition on the glass-forming ability (GFA), microhardness, and corrosion resistance of Mg60−xCu40Ndx (x = 5, 10, 15, 20, and 25, at%) alloys were investigated by differential scanning calorimetry, Vickers-type hardness tests, and electrochemical methods. The results suggest that the GFA and microhardness of the amorphous alloys increase until the Nd content reaches 20at%. The corrosion potential and corrosion current density obtained from the Tafel curves indicate that the Mg35Cu40Nd25 ternary alloy exhibits the best corrosion resistance among the investigated alloys. Notably, nanoporous copper (NPC) was synthesized through a single-step dealloying of Mg60−xCu40Ndx (x = 5, 10, 15, 20, and 25) ternary alloys in 0.04 mol·L−1 H2SO4 solution under free corrosion conditions. The influence of dealloying process parameters, such as dealloying time and temperature, on the microstructure of the ribbons was also studied using the surface diffusivity theory. The formation mechanism of dealloyed samples with a multilayered structure was also discussed.

High-Efficiency Inhibition of Gravity Segregation in Al–Bi Immiscible Alloys by Adding Lanthanum

The inhibition of gravity segregation has been a long-standing challenge in fabrication and applications of homogeneous immiscible alloys. Therefore, the effect of rare-earth La on the gravity segregation of Al–Bi immiscible alloys was investigated to understand the homogenization mechanism. The results showed that the addition of La can completely suppress the gravity segregation. This is attributed to the nucleation of Bi-rich liquid phase on the in-situ produced LaBi2 phase and the change of the shape of LaBi2@Bi droplets. In addition, a novel strategy is developed to prepare the homogeneous immiscible alloys through the addition of rare-earth elements. This strategy not only is applicable to other immiscible alloys, but also is conducive to finding more elements to suppress the gravity segregation. This study provided a useful reference for the fabrication of the homogeneous immiscible alloys.

Melt structure of Bi20Sb80 alloy and its effect on the solidification

ABSTRACT In this article, the temperature dependence of electrical resistivity (ρ-T) of Bi20Sb80 alloy was investigated by DC four-probe method. The results showed that there were two kinds of liquid–liquid structure transition (L-LST) in liquid Bi20Sb80 alloy, one was irreversible at high temperature above the liquids (815–1069°C) and the other was reversible near the melting point (600–720°C). The anomalous points on differential scanning calorimetry curve matched well with that on ρ-T curve which verified the effectiveness of the resistivity experiment. L-LST of high temperature refined the solidification organisation of Bi20Sb80 alloy to a certain extent.