Papers by Author: Lai Wang

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Authors: Ning Zhao, Jian Hui Wang, Hai Tao Ma, Lai Wang
Abstract: The microstructure evolution and the growth behavior of intermetallic compounds (IMCs) at Sn-xZn-2Cu/Cu (x=6.5, 8.8, 10 and 12, wt%) interfaces during soldering were investigated. The results indicate that planar Cu5Zn8 layer is formed at each interface of Sn-8.8Zn-2Cu/Cu, Sn-10Zn- 2Cu/Cu and Sn-12Zn-2Cu/Cu couples for all soldering time. However, for Sn-6.5Zn-2Cu/Cu couple, it is Cu5Zn8 phase that formed at the interface within shorter soldering time (1 h and 4 h), but the interfacial reaction products become a double layer structure of Cu6Sn5 phase (near Cu substrate) and CuZn phase (near solder) for longer soldering time (25 h and 49 h). The thickness of IMC layers in all couples increases exponentially with the soldering time. It is also found that for the same soldering time, the thickness of IMC layers increases with increasing Zn content in the solder.
543
Authors: Wen Yan Liu, Lai Wang, Ji Bin Liu, Ping He Li, Kai Miao, Rong Dong Han
Abstract: Microstructures and toughness of simulated coarse grain heat-affected zone of hot continuously rolled copper-bearing steel were investigated using physical simulation. The results showed that brittlement is easy to happen in the region of CGHAZ with slower thermal cycles (t8/5≥45s). Granular bainite transformed from austenite led to brittlement. The dimensions of granular martensite and austenite (M-A) constituents are main factors influencing the impact toughness. There is no visible effect on the toughness when the dimensions of M-A constituents are less than 1μ m. However, the toughness decreases greatly once the dimensions exceed 1μ m. Therefore, decreasing the dimensions of M-A constituents by controlling weld heat input will do good to improve the impact toughness of copper-bearing steel.
910
Authors: Ji Bin Pei, Yun Feng Zhao, Dong Ming Li, Jie Zhao, Lai Wang
Abstract: A statistical analysis of creep rupture data for 2.25Cr-1Mo steel was performed. The scattering of creep rupture data was represented by Z-parameter method based on Manson-Haferd method. With the application of Z-parameter, reliability design for allowable stress of creep rupture strength was carried out according to design life. The higher the value of confidence level, the lower the allowable stress. In comparison with safety factor method and minimum rupture strength method, it can be seen that reliability design based on Z-parameter is more agree with experimental data than other methods. Reliability design provides more precise results by considering the real distribution of creep rupture property and provides more flexible choice for design due to the need of safety and economy.
507
Authors: Xue Min Pan, Ning Zhao, Rui Fang Ding, Guang Lin Wei, Lai Wang
Abstract: The liquid structure of two lead-free solder molten alloys, Sn-0.5Cu and Sn-1.8Cu (wt.%), have been investigated using X-ray diffraction method. The main peak for liquid structure of Sn-0.5Cu is similar to that of pure Sn. A pre-peak has been found in the low Q part on the structure factor S(Q) of Sn-1.8Cu tested under 320°C and the pre-peak decreases its intensity with increasing temperature, but it disappeared finally when the testing temperature reached 350°C. The microstructure of the solder matrix as well as interfacial reaction between liquid solders and Cu substrate was also studied. The structural unit size corresponding to the pre-peak almost equals to magnitude of crystal planar distance of Cu6Sn5 phase. The appearance of a pre-peak may be due to existence of clusters with Cu6Sn5-phase-like structure in the melt. Quantity and size of clusters increases with decreasing temperature but their structural unit size remains constant. Cu6Sn5 phases develop from incorporating and growing of the clusters during solidification, thus result in the correlation between liquid structure and solid microstructure.
1385
Authors: Xue Min Pan, Ning Zhao, Rui Fang Ding, Guang Lin Wei, Lai Wang
Abstract: The liquid structure of two lead-free solder Molten alloys, Sn-0.5Cu and Sn-1.8Cu (wt.%), has been examined using X-ray diffraction method. The main peak for liquid structure of Sn-0.5Cu is similar to that of pure Sn. A pre-peak has been found in the low Q part on the structure factor S(Q) of Sn-1.8Cu tested under 320°C, but it disappeared finally when the testing temperature reached 350°C. The both viscosity was measured using a torsional oscillation viscometer. It was found that the anomalous variations of viscosity had a direct relation with the transition of the liquid structure, which is consonant with the results of high temperature X-ray diffraction. The microstructure of the solder matrixes as well as interfacial reaction between liquid solders and Cu substrates was also studied. The results show that particle-like Cu6Sn5 intermetallic compounds (IMCs) emerge in Sn-1.8Cu solder matrix. The IMC layer at Sn-1.8Cu/Cu joint is thicker than that at Sn-0.5Cu/Cu interface. The correlative effect of liquid structure on phase evolution in the solder joints is analyzed.
679
Authors: Hai Tao Ma, Wen Ping Huang, Lai Wang
Abstract: In this paper, a new method named infiltration was applied to fabricate W-Cu surface modified layers of copper mould firstly in order to promote the life span of the continuous casting machine (CCM) mould. Our efforts concentrated on fabricating the W-Cu modified layers on the surface of mould copper plate by presintering and infiltration under inert gases. The W particle size and sintering temperature of W skeleton were adjusted to gain homogeneous microstructure of W-Cu modified layers. The results show that homogeneous microstructure of W-Cu modified layers can be obtained with the method of presintering and infiltration. For the excellent microstructure of W-Cu modified layers, the suitable tungsten particle size is 300 meshes and the optimal presintering temperature is about 1300°C. W-Cu modified layers have good bonding strength with copper substrate.
1213
Authors: Shuang Qi Han, Jie Zhao, Lai Wang, Hong Bo Gao
Abstract: In this paper, a Z-parameter method is proposed to relate creep rupture data and microstructure deterioration of three low carbon steels: Cr5Mo, 12Cr1MoV and 20 steels. A new analytic expression of the Larson-Miller parameter verse stress is supposed as: P =Z + C1 lgσ + C2 σ, where C1 and C2 are constants which determine the shape of the curves and related to materials, and the value of parameter Z represents the magnitude deviated from the master curve which corresponds with the deterioration in rupture properties. As the deterioration in rupture properties closely connects with the degradation of microstructure, namely the spheroidization of carbides in pearlite style steel, a linear relationships have been found between the value of Z-parameter and the level of spheroidization E which can be expressed as: Z = a1 + a2 E.
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