On Post - Weld Heat Treatment of a Single Crystal Nickel - Based Superalloy Joint by Linear Friction Welding

Abstract

Three types of post-weld heat treatment (PWHT), i.e. solution treatment + primary aging + secondary aging (I), secondary aging (II), and primary aging + secondary aging (III), were applied to a single crystal nickel-based superalloy joint made with linear friction welding (LFW). The results show that the grains in the thermomechanically affected zone (TMAZ) coarsen seriously and the primary γ' phase in the TMAZ precipitates unevenly after PWHT I. The primary γ' phase in the TMAZ and weld zone (WZ) precipitates insufficiently and fine granular secondary γ' phase is observed in the matrix after PWHT II. After PWHT III, the primary γ' phase precipitates more sufficiently and evenly compared to PWHTs I and II. Moreover, the grains in the TMAZ have not coarsened seriously and fine granular secondary γ' phase is not found after PWHT III. PWHT III seems more suitable to the LFWed single crystal nickel-based superalloy joints when performing PWHT.