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Effects of Pulse Current Treatment on the Precipitation Behavior of Carbides for GH3044

Author: WangZuoZuo
Tutor: CuiWenFang;WangLei
School: Northeastern University
Course: Materials Science
Keywords: GH3044 alloy pulse current treatment aging treatment carbide on the grain boundary
CLC: TG132.32
Type: Master's thesis
Year: 2009
Downloads: 67
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Abstract


The main effects of pulse current treatment on metallic materials are refining, electro plasticity, and amorphousizing. The pulse current was performed on the superalloy GH3044 in the present research. The microstructure under different treatment parameters were examined and evolving mechanisms of the carbides were also discussed.The instrument used in this study was the HPC-5 pulse current instrument, with a current intensity of 0-5kA, a pulse frequency of 2-50Hz and a pulse width of 15-30μs. The temperature variation during pulse current treatment was in situ measured by a thermal-couple attached on the specimen.The results showed the precipitation temperature of M23C6 type carbide in GH3044 alloy could be decreased by pulse current treatment of high current intensity. M23C6 type carbides uniformly precipitated along grain boundaries in the specimen treated by pulse current intensity of 4kA, frequency of 5Hz, and pulse width of 15μs for 1hour. Under such treatment parameter, the temperature rise of the specimen was 560℃. But there was no precipitation of M23C6 type carbides along the grain boundary in the specimen aged at 560℃for 1 hour. The temperature rise of specimen was 745℃when it was treated by pulse current intensity of 5kA, frequency of 5Hz, and pulse width of 15μs for 5 hours, the volume percentage of precipitated M23C6 type carbides was 16.97%, which was much more than that of 6.18% only aged at 745℃for 5 hours.It has been also found that the precipitation of M23C6 type carbides along grain boundaries could be inhibited by pulse current treatment too. When the specimen was treated by pulse current intensity of 2kA, frequency of 45Hz, and pulse width of 15μs for 5 hours, the temperature of specimen was 805℃, and the volume percentage of precipitated phase is 1.23%, which is much less than that of 6.54% aged at 805℃for 5 hours.Based on the experimental results, it can be seen that precipitation of M23C6 type carbides in GH3044 alloy can be promoted or to inhibited the by controlling the parameters of pulse current treatment. The main reason of these phenomena can be considered as both the thermodynamic condition and dynamic condition of the precipitation of M23C6 type carbides in GH3044 alloy can be changed by the pulse current treatment. And the phase equilibrium states would be also broken, so that both the starting and peak temperatures of precipitation will be decreased. During electric aging process, the uniformity and speed of precipitation will be greatly improved.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > The alloy learn with a variety of properties of alloys > Special physical properties of alloys > Special thermal properties of alloys > Melting point alloys , refractory alloy , high temperature alloys
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