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Feng G.,Harbin Institute of Technology | Li Z.,Harbin Institute of Technology | Xu K.,Harbin Institute of Technology | Liu W.,AVIC Harbin Dongan Engine Co.
Hanjie Xuebao/Transactions of the China Welding Institution

Vacuum brazing of SiC ceramic was conducted using Ti-Zr-Ni-Cu solder. The interface microstructure and its formation mechanism was investigated. Scanning electron microscope (SEM) was used to observe the joint microstructure and conduct local energy spectrum analysis. The results show that the products in the joint interface were mainly TiC, Ti5Si3, Zr2Si, Zr(s, s), Ti(s, s)+Ti2(Cu, Ni) and (Ti, Zr)(Ni, Cu) phases. The microstructure of the joint interface could be expressed as SiC/TiC/Ti5Si3+Zr2Si/Zr(s, s)/Ti(s, s)+Ti2(Cu, Ni)/(Ti, Zr)(Ni, Cu). The brazing process could be divided into five stages: physical contact between the solder and substrate, melting of solder and formation of reaction layer on the ceramic side, continuous diffusion of melted solder into the substrate, thickness increasing of reaction layer, composition homogenization, ending of reaction on ceramic side and formation of hypereutectic structure, solidification of intermetallic compounds in the center of joint. The shear strength of the joint brazed at 960°C for 10min reached 110 MPa. Source

Wang S.-T.,Harbin University of Science and Technology | Yang P.-W.,Central South University | Liu H.-H.,AVIC Harbin Dongan Engine Co. | Liu C.-M.,Central South University
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology)

To investigate the effect of Zn on microstructures, tensile mechanical properties of extruded Mg-xZn- 2.8Nd-0.6Zr-0.6Cd alloy, the optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and universal tensile test machine were introduced. The mechanical properties of alloys with different Zn contents were compared and discussed. The results show that the grain size decreases as the content of Zn increases, followed with a bimodal grain microstructure, and the tensile strength is increased in general. The yield strength of alloy B is higher than that of alloy C because of the change of atomic ratio of Zn/Nd. The ratio of Zn/Nd in alloy B is 1.2 and the nominal ratio is 3.10, but it is 3.03 and 4.11 in alloy C respectively, which causes the number of β1′ phase precipitation in alloy B to be more than that in alloy C. Alloy D shows the highest yield strength and ultimate tensile strength, which are 340 MPa and 363 MPa, respectively, and the elongation is kept up to 9%. Source

Li Z.,Harbin Institute of Technology | Xu X.,Harbin Institute of Technology | Liu W.,AVIC Harbin Dongan Engine Co. | Lu Z.,AVIC Harbin Dongan Engine Co.
Hanjie Xuebao/Transactions of the China Welding Institution

The effect of joint clearance on microstructures and property of SiC ceramics brazed with Ti-Zr-Ni-Cu brazing filler was studied by means of SEM, EDS and XRD. The joint microstructure from SiC ceramics to the center of brazing seam are TiC, Zr(s, s), Ti5Si3+Zr2Si, Ti(s. s)+Ti2(Cu, Ni) and (Ti, Zr) (Ni, Cu) successively. When the joint clearance is 30 μm~50 μm, Si reacts with Ti and Zr element, and produces a small quantity of tiny needlelike silicon compounds. Homogeneous solid solution is full of the brazed joint. The mechanical property is superior and the shear strength can reach 117 MPa. When the joint clearance is less than 30 μm, longstring silicon compounds are generated, and run through the brazing beam. Meanwhile, successive and thick TiC layer is produced. Both of these two factors lower the mechanical property. When the joint clearance is more than 50 μm, Ti-based intermetallic increases and eutectic compounds are produced, which reduce the mechanical property. Source

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