Fatigue strain mapping via digital image correlation for Ni-based superalloys: The role of thermal activation on cube slip

Abstract

A deformation mechanism map for a Ni-based superalloy is presented during cyclic loading at low (300°C), intermediate (550°C), and high (700°C) temperatures for low (0.7%) and high (1.0%) applied strain amplitudes. Strain mapping is performed via digital image correlation (DIC) during interrupted fatigue experiments at elevated temperatures at 1, 10, 100 and 1000 cycles, for each specified loading and temperature condition. The DIC measurements are performed in a scanning electron microscope, which allows high-resolution measurements of heterogeneous slip events and a vacuum environment to ensure stability of the speckle pattern for DIC at high temperatures. The cumulative fatigue experiments show that the slip bands are present in the first cycle and intensify with number of cycles; resulting in highly localized strain accumulation. The strain mapping results are combined with microstructure characterization via electron backscatter diffraction. The combination of crystal orientations and high-resolution strain measurements was used to determine the active slip planes. At low temperatures, slip bands follow the {111} octahedral planes. However, as temperature increases, both the {111} octahedral and {100} cubic slip planes accommodate strain. The activation of cubic slip via cross-slip within the ordered intermetallic γ' phase has been well documented in Ni-based superalloys and is generally accepted as the mechanism responsible for the anomalous yield phenomenon. The results in this paper represent an important quantifiable study of cubic slip system activity at the mesoscale in polycrystalline γ-γ' Ni-based superalloys, which is a key advancement to calibrate the thermal activation components of polycrystalline deformation models.

Tailoring the Properties of a Ni-Based Superalloy via Modification of the Forging Process: an ICME Approach to Fatigue Performance

“…Each SEM was subjected to a single fatigue loading cycle via crystal plasticity to capture the micro-mechanical fields relative to each of microstructure. Based on prior digital image correlation of this material [68], it was observed that the slip bands form during the first loading cycle (and the number of slip bands were constant with respect to number of cycles for this particular loading). One cycle of the crystal plasticity simulation is sufficient to determine the heterogeneities in the stress distributions relative to the microstructural features [40], and the resulting micromechanical fields after one loading cycle are used for fatigue modeling purposes.…”

Digital image correlation for microstructural analysis of deformation pattern in additively manufactured 316L thin walls

“…Advanced characterization techniques have emerged in the last decades, enabling the tracking of the deformation fields at the grain scale with applied loading by simultaneously combining digital image correlation (DIC) and Electron Backscatter Diffraction (EBSD) analysis [28]. Few investigations were performed at the scale of the grains for AM materials.…”

A DIC-Based Study on Fatigue Damage Evolution in Pre-Corroded Aluminum Alloy 2024-T4

“…Digital image correlation (DIC) is an optical method which can quantify the deformation field on the specimen surface with the advantages of providing full-field, real-time, and non-contact measurements, as well as flexibility [27,28,29,30]. The method has been successfully applied to observe damage and failure in metallic materials during fatigue tests [31,32]. Short cracks during intergranular stress-corrosion cracking of austenitic stainless steel were detected by DIC [33].…”