Evaluation of Intergranular Liquid Phase Distribution and Its Relationship to Hot Cracking

实验计划是表征一系列含铌镍合金的晶界化学性质，然后使用典型的钨电弧焊快速加热和冷却循环对这些晶界进行熔化和再凝固。在加热和冷却过程中，在选定的温度下测定液体化学、液相分布（LPD）和液体体积分数。液体的凝固行为将根据其共晶或固相温度及其最终凝固产物（通常为Laves相）来表征。这种行为与平衡的偏差将通过与等温处理的比较来确定。热裂敏感性将通过使用热延性试验测量零延性温度来确定。拟议的研究将提供关于若干基本和技术问题的资料。它将展示LPD在非平衡冷却阶段是如何演变的，以及热循环是如何通过控制扩散来决定LPD的。它将确定晶界化学对晶间液相化学、液相体积分数和LPD的作用。它还将显示这些与镍合金（如718）的晶间热裂的相关性，718是燃气涡轮喷气发动机的关键材料。

The experimental plan is to characterize the grain boundary chemistry of a series of Nb-bearing nickel alloys and then melt and resolidify these boundaries using a rapid heating and cooling cycle typical of a tungsten-arc weld. The liquid chemistry, liquid phase distribution (LPD), and volume fraction of liquid will be determined at selected temperatures during heating and cooling. The solidification behavior of the liquid will be characterized in terms of its eutectic or solidus temperature and its terminal solidification products, typically a Laves phase. The deviation of this behavior from equilibrium will be determined by comparison to isothermal treatments. The hot cracking susceptibility will be determined by measuring the nil ductility temperature using a hot ductility test. The proposed research will provide information on several fundamental and technical issues. It will show how the LPD evolves during the nonequilibrium stage cooling and how the thermal cycle dictates the LPD through its control of diffusion. It will identify the role of grain boundary chemistry on intergranular liquid phase chemistry, liquid phase volume fraction, and LPD. It will also show the correlation of these to intergranular hot cracking in nickel alloys such as 718, a critical material in gas turbine jet engines.