In-Situ Monitoring of Phase Transition and Microstructure Evolution in Ni-Based Superalloys by Electrical Resistivity: Direct Comparison With Differential Scanning Calorimetry and Application to Case Studies

Abstract

In this study, resistivity measurements are made during continuous heating and cooling on four different Ni-based superalloys of different grain structures and with different phases (i.e., γ′ and carbide). The results are directly compared with differential scanning calorimetry (DSC) profiles to identify the material’s resistivity response. The resistivity measurements have been performed using an electro-thermal mechanical testing (ETMT) system having a capability of heating and cooling a sample at a rate of up to 100 K/s by Joule heating, which is not possible with standard heating methods used in previous in-situ microstructure analysis approaches. By comparing different precipitate variations and thermal histories, γ′ volume fraction and precipitate number density are found to be the most important factors determining the resistivity of the materials. In-situ resistivity measurement was applied to several case studies to show that it can provide microstructural information in complex high temperature experiments.

Multi-length-scale study on the heat treatment response to supersaturated nickel-based superalloys: Precipitation reactions and incipient recrystallisation

“…Hence the change of resistivity can be solely interpreted by the phase transition that occurred during heat treatment [33], i.e. the γ/γ reaction in this case where the precipitate phase obtains a higher resistivity value [34]. The heating and cooling cycle was given to ABD-900AM for the super-solvus 1 heat treatment is consistent with the synchrotron experiment listed in Table 2.…”

“…A resistivity inflection is induced by structural change by either a phase transition and/or deformation [33,50]. For superalloys, a zero-load resistivity measurement is frequently used to interpret the γ/γ reaction [32] due to a difference in resistivity between the γ and γ phases, where the latter obtains a higher value [34]. For the identification of the onset temperature of the resistance increase, the drastic increase of resistance from the first heating curve is analysed.…”