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.
