In-Situ observation of primary γ′ melting in Ni-base superalloy using confocal laser scanning microscopy

High-Temperature Confocal Laser Scanning Microscopy (HT-CLSM) was used to observe the initiation of incipient melting of primary γ′ in a Ni-base superalloy, and to quantitatively determine the liquation temperature. Specimens were cycled using different heating rates (5 and 50 °C/s) to peak temperatures of 1200 and 1300 °C to observe the influence of rapid heating on the development in the γ′-morphology. It was found that rapid heating prevented the dissolution of primary γ′, which melts leading to constitutional liquation and the formation of dendritic γ′ at the grain boundaries upon cooling. These observations are discussed in terms of the microstructural development of Nickel-based superalloys during welding, and their potential influence on the properties.

Research Highlights
► Direct observation of γ′-melting was performed during rapid heating.
► A dendritic γ′-structure forms at the grain boundaries due to dynamic heating.
► The microstructural development is dependent on the heating rate.
► High temperature confocal scanning microscopy can be used to visualise γ′-melting.