Alloy Development of Nickel-Based Superalloy Weld Filler Metals Using Computational Thermodynamics

摘要

Weld repairs of gamma-prime-strengthened nickel-based superalloys such as IN738, IN939, Rene80 and GTD111 typically use lower strength solid solution filler metals, thereby limiting the weld repair to low stress regions. The use of gamma-prime-strengthened filler metals is also limited because of issues related to weldability and as-welded properties. These problems are often related to the formation of deleterious phases during welding. This study was aimed at examining alloy modifications to gamma-prime-strengthened alloys that will avoid the formation of these undesirable phases and will yield improved filler metal alloys for welding. Computational thermodynamics was used in the study to examine the influence of alloy modifications on the phase stability of nickel-based superalloys. This approach can take into account many of the complex interactions among alloying additions, and it provides a simple and efficient means for alloy optimization. The results of the calculations are presented. The effect of alloying additions on the stability of carbides and undesirable phases such as eta phase, sigma phase, and P-phase is described. The results often show very complex interactions but they can be readily explained and understood. These calculations show the potential of using computational thermodynamics as a valuable tool in alloy design and optimization.