Cyclic plasticity and fatigue damage of CrMnFeCoNi high entropy alloy fabricated by laser powder-bed fusion

TL;DR

This study investigates the cyclic plasticity and fatigue damage mechanisms in CrMnFeCoNi high-entropy alloy fabricated by laser powder-bed fusion, revealing microstructural influences on fatigue resistance and crack propagation.

Contribution

It provides new insights into the link between print process parameters, microstructure, and fatigue behavior in high-entropy alloys.

Findings

Dislocation slip is the dominant cyclic plasticity mechanism.

Surface finish delays crack initiation and influences fatigue life.

Scan strategies significantly affect grain structure and fatigue crack propagation.

Abstract

The CrMnFeCoNi high-entropy alloy is highly printable and holds great potential for structural applications. However, no significant discussions on cyclic plasticity and fatigue damage in previous studies. This study provides significant insights into the link between print processes, solidification microstructure, cyclic plasticity and fatigue damage evolution in the alloy fabricated by laser powder bed fusion. Thermodynamics-based predictions (validated by scanning transmission electron microscopy (STEM) energy dispersive X-ray spectroscopy (EDX)) showed that Cr, Co and Fe partition to the core of the solidification cells, whilst Mn and Ni to the cell boundaries in all considered print parameters. Both dislocation slip and deformation twinning were found to be responsible for plastic deformation under monotonic loading. However, the former was found to be the single dominant mechanism for cyclic plasticity. The surface finish helped to substantially delay the crack initiation and cause lack-of-fusion porosity to be the main source of crack initiation. Most significantly, the scan strategies significantly affect grain arrangements and grain dimensions, leading to noticeable effects on fatigue crack propagation; in particular, the highest resistance crack propagation was seen in the meander scan strategy with 0{\deg} rotation thanks to the most columnar grains and the smallest spacing of grain boundaries along the crack propagation path.