Welding and Weld Repair of Single Crystal Gas Turbine Alloys
FEAA064

In August of 2001 the National Energy Technology Laboratory entered into a field office work agreement with the Oak Ridge National Laboratory to study weld repairs in alloys used for gas turbine blades.

Single crystal alloy gas turbine blades are required in advanced turbines because they provide the capability to withstand the high turbine rotor inlet temperatures (1427 Centigrade/2600 Farenheit) required to meet next generation efficiency goals. Replacement costs for blades that have failed are extremely high due to a combination of alloy cost and low casting yields. Repair by welding is the best option if techniques can be developed or improved.

The purpose of this project is to improve the quality of welds in alloys used for turbine blades by:

• Employing computational thermodynamics to investigate mechanisms for stray crystal formation in single crystal weld repairs.

• Performing thermo-mechanical simulations to evaluate cracking propensity of welds as a function of microstructure, composition and thermal conditions.

• Modeling microstructure evolution during welding of single crystal alloys.

• Experimentally testing process improvements to minimize stray grain formation and improving heat treatment stability.