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Wu C.,Central South University | Yi D.,Central South University | Xu C.,Central South University | Zhou J.,Central South University | Weng W.,Fuda Alloy Materials Co.
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2013

The microstructure of Ag-Sn-La alloy powder after oxidation was investigated by XRD, OM and SEM. The results show that Ag, SnO2 and La2Sn2O7 phases are formed in Ag-Sn-La alloy powder after oxidation. Ag-Sn-La alloy powder has different oxidation kinetic characters, oxidation microstructures and oxidation mechanisms due to the different contents of alloying agent. The starting oxidation temperature of Ag-5.2Sn-3.4La alloy powder is 350°C and the oxidation velocity is fast. Both element Sn and La are oxidized in situ and strip oxides are formed due to the fast oxidation of element La during the oxidation of Ag-5.2Sn-3.4La alloy powder. The oxidation velocity of Ag-6.87Sn-1.28La alloy powder is slow when the temperature is from room temperature to 300°C and that is fast when the temperature is above 300°C. Both element Sn and La are oxidized in situ and the formed oxides are uniformly distributed in the silver matrix. The starting oxidation temperature of Ag-9.26Sn-0.44La alloy powder is 567°C and the oxidation velocity is slow. Element La is oxidized in situ and element Sn diffuses from the inner to the surface due to the driving of concentration gradient. La oxides are uniformly distributed in the silver matrix and Sn oxides are mainly distributed on the grain boundary after Ag-9.26Sn-0.44La alloy powder oxidation.

Wu C.P.,Central South University | Yi D.Q.,Central South University | Goto S.,Akita University | Xu C.H.,Central South University | And 3 more authors.
Materials and Corrosion | Year: 2014

The oxidation behavior of Ag-5.08Sn-3.15Sb and Ag-6.84Sn-1.25Sb alloy powders was investigated in air at 800 °C. The thermal gravimetric analysis (TGA) results confirmed that the starting oxidation temperature of Ag-5.08Sn-3.15Sb and Ag-6.84Sn-1.25Sb alloy powders was 670 and 720 °C, respectively. The oxidation kinetic results suggested that the oxidation behavior of Ag-Sn-Sb alloy followed a parabolic rate and the oxidation rate of Ag-5.08Sn-3.15Sb alloy powders was 3.2 times larger than that of Ag-6.84Sn-1.25Sb alloy powders. XRD results indicated that the formed Sb 2O3 would react with the Ag matrix forming AgSbO 3. SEM-EDS observations indicated that the formed oxideswere primarily distributed on the grain boundaries and the formed AgSbO3 particles nailed into the SnO2 particles. In addition, the oxidationmechanism of Ag-Sn-Sb alloy powders and the effect of Sb on oxidation behavior of Ag-Sn alloy powders were also discussed. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pang Y.,Central South University | Xia C.,Fuda Alloy Materials Co. | Wang M.,Central South University | Wang M.,Key Laboratory of Nonferrous Metal Materials Science and Engineering | And 6 more authors.
Journal of Alloys and Compounds | Year: 2014

The properties and microstructure of Cu-Cr alloy with Zr and (Ni, Si) additions were investigated. Improvements of peak-hardness and softening resistance are achieved with Zr and (Ni, Si) additions in the Cu-Cr alloy, while only a slight decrease in conductivity is brought out. Good balance of hardness and electrical conductivity, which reach to 177 HV and 82.2% IACS respectively, can be obtained in the Cu-Cr-Zr-Ni-Si alloy after 80% cold rolling and 450 C aging for 360 min. The solutes-rich particles in cast microstructure and aged precipitates are refined and homogeneously distributed with the addition of alloying elements. Stacking fault energy of the Cu-Cr alloy decreases with the additions of Zr and (Ni, Si) elements, leading to easy and extensive occurrence of stacking faults and twins. Precipitate morphology of Cu-Cr alloy can be modified by the additions of alloying elements, which is associated with the interface energy of precipitates in the over-aged Cu-Cr-Zr and Cu-Cr-Zr-Ni-Si alloy. © 2013 Elsevier B.V. All rights reserved.

Xie J.,Fuda Alloy Materials Co. | Xie J.,Central South University | Cao S.,Central South University | Bai X.,Fuda Alloy Materials Co. | And 3 more authors.
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2014

This work shows the feasibility of cold gas-spray technique for the manufacturing of industrial electrical contact materials. Microstructure and mechanical properties of the material were investigated using optical microscopy, scanning electron microscopy, hardness test and shearing test. Results show that the bonding strength of the material is determined by the hardness of substrates. High hardness results in low bonding strength. Bonding strength of AgSnO2 sprayed onto aluminum is the best, followed by copper and brass. The bonding strength of silver graphite is not as good as that of silver tin-oxide. The most appropriate particle size is 20 μm for a bulk particle according to the optimization. Copyright © 2014, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.

Wu C.,Central South University | Wu C.,Fuda Alloy Materials Co. | Yi D.,Central South University | Weng W.,Fuda Alloy Materials Co. | And 3 more authors.
Materials and Design | Year: 2015

Ag/Ni electrical contact materials tend to be weld together under high current and/or high temperature, which was a key problem to restrict the usage of Ag/Ni electric contact materials. Arc erosion characteristics of Ag/12Ni electrical contact material after 50,000 operations under direct current 19 V, 20. A and resistive load conditions were investigated. The result indicated that the probability distribution and change trend of arc energy and arc time during 50,000 operations were similar and the relationship between arc time and arc energy followed exponential function. On the one hand, "Crater" type erosion pit, island-like melted silver, pore, crack and coral-like structure spitting were observed on erosion surface of Ag/Ni contact materials. On the other hand, distribution of Ag and Ni element on molten pool of movable contact was different from that of stationary contact. For movable contact, element Ni mainly distributed on melted pool root, whereas element Ag mainly distributed inside of melted pool. For stationary contact, however, element Ni and Ag distributed layer by layer. Furthermore, arc erosion of stationary contact is more serious than that of movable contact. © 2015 Elsevier Ltd.

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