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研究了镍基高温合金Ni-10Cr-15Co-6W-6Mo-4Al-2Ti真空电弧重熔过程中自耗电极熔化特征及电极端部不同区域内Mg的分布。发现在电极侧表面存在着一个重熔金属环,Mg在其中分布相当均匀,而在重熔金属液层及液固两相区内Mg分布则不均匀。金属液层厚度随其在电极端部所处位置而异,其平均值为1—1.5mm。分析结果指出,Mg含量从金属液层/气相界面经液固两相区至原始电极区即随距金属液层/气相界面距离δ_1增加而增加。重熔金属环中Mg含量[Mg]_r及熔化金属液外层(δ_1<0.40mm)中Mg含量均低于重熔锭中Mg含量[Mg]_i。在试验条件下,如自耗电极Mg含量以[Mg]_e代表,则[Mg]_(0.15)=0.18[Mg]_e=[Mg]_r;[Mg]_(0.40)=0.30[Mg]_e=[Mg]_i。真空电弧重熔过程中,Mg挥发主要发生于电极端部熔滴形成阶段,流经电极端面的金属液不能全部暴露于真空下,Mg挥发过程受控于Mg原子由原始电极区向金属液层/气相界面迁移的速度。传质系数K_(12)=0.107cm·s~(-1)。重熔锭中Mg含量[Mg]_i=[Mg]_e exp(-K_(12)·A·γ·W~(-1))。显然,可通过控制电极Mg含量[Mg]_e及熔化速率W来实现最佳Mg控制。

The remelting of consumable electrode and the Mg distribution in various zones at electrode tip during VAR process of a Ni-base superalloy Ni-10Cr-15Co-6W-6Mo-4Al-2Ti were studied. It was found that a remelted metal ring sticks to the electrode surface near tip. The Mg distributes in the metal ring rather homogeneously, but in remelted metal layer or in the liquid-solid binary phase zone heterogenously. The thickness of the remelted metal layer is varied with its position from electrode tip and averaged 1—1.5mm. The Mg content increased gradually with the increase of distance from the metal film/atmosphere interface via liquid/ solid binary phase zone to the unmelted electrode. The Mg concentra-tion either in the remelted metal ring, [Mg]_r, or in the outer layer of remelted liquid metal was less than that in the remelted ingot, [Mg]_i. Under present experimental conditions, [Mg]_(0.15)=0.18[Mg]_e=[Mg]_r; [Mg]_(0.40)=0.30[Mg]_e =[Mg]_i, where [Mg]_(0.15) and [Mg]_(0.40)=Mg concentration in the outer layer of remelted liquid metal at 0.15 and 0.40mm respectively; [Mg]_e and [Mg]_i=Mg concentration in electrode and in ingot respectively. It seems that the Mg is mainly evaporized in the droplet forming period during VAR process. The liquid metal flows round the surface of electrode tip and is unable to expose fully under vacuum. The process of Mg evaporation may be controlled by the transfer rate of Mg atoms from unmelted electrode into the liquid metal film/atmosphere interface. The coefficient of mass transfer K_(12)=0.107 cm·s~(-1). The Mg content in remelted ingot, [Mg]_i=[Mg]_e exp(-K_(12)Aγw~(-1). Thus, the optimum [Mg]_i can be realized by controlling [Mg]_e and the remelting rate w.