Heat treatment is an essential part of manufacturing of Ni-based superalloys as this microstructure optimization gives huge improvement in mechanical properties of the material. Solvus and liquidus temperatures must be defined in order to solutionize and homogenize the γ/γ′ system superalloys during solution treatment, or to apply subsolvus heat treatment. Kinetics of γ′ precipitation and growth is also of interest for adjusting precipitate size during aging treatments. Traditionally, thermal analyses such as differential thermal analysis (DTA) and differential scanning calorimetry (DSC) are used in the first step to determine heat treatment conditions.

However, electrical resistivity is another method that can detect microstructural behaviors at various temperatures. It can be used to define grain growth, dissolution and precipitation kinetics of γ′ phase, and to observe change in microstructure during overheating mechanical testing in a non-destructive way. Several studies have made attempt to extract microstructural information through electrical resistivity measurement. However, the analyses so far have been limited to specific cases and there is a need for comprehensive understanding to make the best use of this method.

In this study, resistivity measurements are made during heating and cooling of Ni-based superalloy samples and the results are compared with DSC profile to identify the material’s resistivity response. The resistivity measurements have been performed using an electro-thermo mechanical testing (ETMT) system having a capability of heating and cooling sample at rate of 100 K/s by Joule heating, which is not possible in standard heating methods used in most of the previous studies. Materials with different grain size and thermal history presented different resistivity profile in the same heating/cooling condition. Phase transition and microstructure evolution will be discussed using both resistivity and DSC results. Several case studies using a combination of resistivity measurement and simultaneous mechanical testing will be introduced.