| With the maturation and development of China’s turbo generator, the materials formaking turbine generator rotor is higher required. Cu-Ni-Be-Zr wedge copper alloy ismainly used as the rotor materials, which plays an important role in the development ofturbo generator. Zhenjiang Siyang special metal materials company is the main productionbase of wedge copper alloy of turbo generator. Recently, during the process of the researchand development of Cu-Ni-Be-Zr wedge copper alloy, ninety percent of the Cu-Ni-Be-Zrwedge copper alloy in that company, calculated by the ultrasonic detection and analysis,testing, can not meet the requirements of ultrasonic detection. This situation seriouslyhampered the production of Cu-Ni-Be-Zr wedge copper alloy and the development of turbogenerator.This paper aimed at doing overall research on the failure cause of Cu-Ni-Be-Zr wedgecopper alloy, exploring the reasons why the unused materials were not qualified throughultrasonic examination. Through system and overall analysis of melting and casting process,pouring process design, pressure processing, solid solution treatment, ageing treatment andcold deformation, try to find out how the above processes have effect on the microstructureand properties of Cu-Ni-Be-Zr wedge copper alloy. It is possible, by means of theseresearches, to work out the optimal processing so that the manufacturing and processing canbe under overall control. This helps to improve the comprehensive performance andqualified ratio of ultrasonic detection. Moreover, this thesis, from the perspective ofdynamics also does research on the phase transformation of Cu-Ni-Be-Zr wedge copperalloy. The current research is based on the method of combining the qualitative analysis andquantitative description to optimize the hot treatment of Cu-Ni-Be-Zr wedge copper alloy.(1) The reason why the ultrasonic testing has unqualified waveform can be divided intothree cases below. First, the disparity between the first bottom wave and the second bottomwave is larger. Second, there exist forest waves among the normal waves. Third, thereappear no bottom waves. After the field observation and analysis, the gating system oncasting exist serious insufficiency. First, the height of the riser is decreased. Then, toppouring way was instead by bottom pouring. To make chemical composition mixed, theholding time before forging was appropriately prolonged, the hot deformation duringforging was increased and the cold deformation was enhanced10-15%. After overallanalysis and improvement, the qualified rate of ultrasonic testing reaches to90%, which greatly improves the productivity and saves the cost for the enterprise. Afterwards, the industrial application of Cu-Ni-Be-Zr wedge copper alloy in industrial application returns to normal.(2) This thesis also does research on dynamics of phase transformation in Cu-Ni-Be-Zr wedge copper alloy. The results show that:the variation of conductivity can accurately reflect the new phase transition rate of Cu-Ni-Be-Zr wedge copper alloy during ageing treatment. Then the experimental results show that the varied trends of conductivity as well as the volume fraction of precipitations consist with the ageing time. The isothermal transformation curve of Cu-Ni-Be-Zr wedge copper alloy is consistent with the characteristics of "C" curve. As can be seen from the "C" curve, when the ageing temperature is at490℃, the transformation rate is the fastest to reach the ending. And the empirical equation to describe the phase transformation kinetics "S" curve is: f=1-exp(-0.615t0.279). Then the equation of reaction conductivity changing with the ageing time isσ-=36.3+29.76[1-exp(-0.617t0.294)].(3)Experimental results show that, by930℃×1.5h solid solution and30%cold deformation and490℃×2.5h ageing treatment, Cu-Ni-Be-Zr wedge copper alloy can get the best overall performance. The values of hardness and electrical conductivity are HB271and67.6%IACS. During the phase transformation process, the solid solution elements precipitated as the second precipitates. Precipitations include Be2Cu、Be17Zr2、ZrCu、 Ni7Zr2、Be21Ni5and so on. The phase transformation process can be effectively controlled by changing the ageing temperature and the time. Consequently, the optimal ageing high-strength alloy can be achieved. The optimal experimental parameters obtained after ageing is corresponding with the date presented from dynamic of phase transformation, which ensures the validity of theoretical research.(4)Compared with Cu-Ni-Be, there exist some changes of Cu-Ni-Be-Zr and Cu-Ni-Be-Cr, by observing the microstructure and properties under the condition of different heat treatment processes after forging of these three kinds of alloys. It shows that low content of alloying elements Zr and Cr can completely dissolve during solid solution treatment, resulting in a solid solution strengthening effect. Besides, Zr and Cr can play a part in fine grains. According to the theory of fine-grain strengthening, the strength and hardness of Cu-Ni-Be-Zr and Cu-Ni-Be-Cr will increase while the electrical conductivity reduces greatly especially when Cr is added. The hardness and electrical conductivity bounce back after ageing treatment by adding Zr or Cr. Meanwhile, Cu-Ni-Be-Zr and Cu-Ni-Be-Cr, compared with Cu-Ni-Be, remain higher strength and the electrical conductivity improves as well. |
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