Effects Of Alloy Composition And Melting Process On Microstructure And Thermal Physical Properties Of Cu-Ni Alloy

With the intensity of smelting reinforced, the protection technology of blast furnace lining becomes increasingly important. The most frequently applied solution is to bury pure copper cooling water jackets with high thermal conductivity in the brickwork to achieve forced cooling and prolong the expectancy of blast furnace.However, pure copper cooling water jacket has three shortcomings that are inevitable.First and foremost, the water jacket is easy to melt in the casting process; in addition,due to the higher temperature in the furnaces, the water jacket is likely to melt provided there is a change in the water amount, water pressure or slight fluctuation of water temperature. Besides, the excessive thermal conductivity of pure copper is apt to yield negative impacts of “air hammer”. Because of the low melting point of pure copper, developing high performance cooling jacket is of vital significance to the development of heat exchange devices like copper alloy with high melting point and high conductivity. Based on copper alloy phase diagram, such elements as Mo, Nb, Y are added to the Cu-Ni alloy to generate Cu-Ni-Mo, Cu-Ni-Nb-Y and Cu-Ni-Nb-Mo alloys. This thesis systematically investigates alloy composition as well as the effects of melting process on microstructure, melting point, thermal conductivity, and hardness of alloy. The main conclusions are as follows:(1)With the same components of copper alloy, the grain of Cu-Ni-Mo alloy made in electric arc melting water-cooled copper crucible process is more coarse and of more stable thermal conductivity than that made in induction quartz glass tube cooling process. The melting point and the hardness of Cu-Ni-Mo alloy made by electric arc melting process are higher.(2)The increase of Mo element in Cu-Ni-Mo alloy has little influence on it in these two melting processes. However, when Mo phase appears in the organization of Cu-Ni-Mo alloy, the melting point rises noticeably.(3)The addition of small amount of rare earth element Y in Cu-Ni-Nb alloy makes the grain of alloy more delicate but the precipitated phase longer. Y element improves alloy thermal conductivity. Whereas Y element has negative influence on the melting point of Cu-Ni-Nb alloy. Y element hardly changes hardness of alloy purely from the perspective of slim grain.(4)In Cu-Ni-Nb-Mo alloy, when the content of Ni element is stable, the thermal conductivity improves as a result of the increase of Nb and Mo, which contributes to the rise of precipitated phase, but the melting point drops.(5)Under the experiment condition, the sequence of various elements’ primary and secondary effect on thermal conductivity and melting point of Cu-Ni-Nb-Mo alloy remains fixed: Ni-Nb-Mo. The effect of Ni on the copper alloy thermal conductivity and melting point is obvious. The more Ni is in copper alloy, the lower the thermal conductivity is and the higher the melting point is. Effects of elements Nb and Mo on copper alloy follow respectively.(6) Under the experiment condition, by comprehensive balance analyzing of orthogonal experiment, the optimal composition of high-conductivity and high-melting point copper alloy is Cu-15Ni-3Nb-2Mo, the thermal conductivity of which is54.70(m·k) and the melting point 1131.59℃.