| Brazing is a joining process that is commonly used for the repair of gas turbine hot section components. Narrow and wide gap braze repair for cobalt-base superalloys X40 with alternative nickel-base filler alloys were successfully developed and characterized, as outlined in this thesis. Narrow gap braze joints were found to contain a primary gamma-Nickel phase with secondary eutectic phases and discrete carboborides. These secondary phases adversely affected the mechanical properties of the joint, particularly ductility. Isothermal heat treatment reduced the size and quantity of the secondary phases, improving the ductility. Prolonged exposure to high temperature in air however, caused a reduction in mechanical properties due to oxidation. Wide gap braze joints were also found to contain a primary gamma-Nickel phase surrounded by secondary eutectic phases and discrete carboborides. The wide gap braze joints had comparable tensile properties to X-40 but performed poorly in high temperature fatigue testing due to the presence of small voids as a result of incomplete wetting of the IN-738 additive alloy powder particles by the braze alloy. |
