Dissolution kinetics of γ′ precipitate in IN738LC nickel base superalloy using arc heat treatment

Nickel base superalloy IN738LC is widely used in power plant industry and gas turbine blade manufacturing.The main strengthening mechanism of this alloy is the precipitation hardness caused by precipitates.These precipitates play an important role in determining the mechanical properties of this alloy and their amount and morphology changes under heat treatment.In this research, in order to investigate the evolution of ' precipitates during heat treatment, a number of solution annealed samples were subjected to arc heat treatment.In this heat treatment, by applying heat caused by a static arc, a temperature ranges from the ambient temperature to above the melting point is created in the sample.Using this process, samples with 100 amp currents were heat treated for 1, 2 and 15 minutes.Electron microscope, image processing and transient heat transfer model with axial symmetry were used for experimental and mathematical investigations.In the following, using the experimental and numerical results simultaneously, a mathematical model for the dissolution kinetics of ' precipitates in the heat-affected zone of these welds was presented.The results of electron microscopy showed that the dissolution rate and shape of precipitates are strongly influenced by the distance from the heat source.The activation energy of dissolution of precipitates increased with increasing time and its value was between 40 and 80 kJ/mol.