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

实验计划是表征一系列含Nb的镍合金的晶界化学，然后使用钨弧焊典型的快速加热和冷却循环来熔化和重新凝固这些晶界。在加热和冷却过程中，将在选定的温度下测定液体的液体化学、液体相分布(LPD)和体积分数。液体的凝固行为将根据其共晶或固相线温度及其最终凝固产物来表征，通常是Laves相。这一行为偏离平衡的程度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塑性试验测量零塑性温度来确定。拟议的研究将提供关于几个基本和技术问题的信息。它将显示LPD在非平衡阶段冷却过程中如何演变，以及热循环如何通过其对扩散的控制来决定LPD。它将确定晶界化学在晶间液相化学、液相体积分数和LPD中的作用。它还将显示这些因素与718等镍合金晶间热裂的相关性，718是燃气轮机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.