Ductility-Dip Cracking Mechanisms in Nickel-Based Alloys

Nickel-based alloys are central to high-temperature structural applications, from turbine engines to nuclear power systems. Ductility-dip cracking (DDC) arises when these alloys experience a marked reduction in ductility over a narrow temperature interval just below their solidus during cooling or sustained thermal exposure. In this range, grain boundaries become preferential sites for sliding and cavitation under applied or residual stress, while intragranular softening and precipitation of low-melting eutectic phases further weaken the intergranular cohesion. The result is the nucleation and propagation of cracks along grain boundaries, often exacerbated by localised segregation of alloying elements, complex thermal gradients and mechanical constraints inherent to welding, additive manufacturing and repairs. Understanding the fundamental interplay between crystallographic orientation, dislocation behaviour and grain boundary character is essential to mitigate DDC in weldments, coatings and laser-deposited structures of nickel-based superalloys.

Research from Nature Portfolio

A seminal statistical investigation employed synchrotron X-ray microdiffraction to map dislocation structures adjacent to ductility-dip cracks in a laser-printed Ni-based superalloy. Analysis of dozens of grains revealed that edge-type geometrically necessary dislocations align parallel to the crack plane, indicating that thermal tensile stresses perpendicular to the scan direction activate slip systems by Schmid’s law. Accumulation of these dislocations at high-angle grain boundaries drives void formation and crack propagation during post-build heat treatment. This work offers a quantitative mechanism linking temperature gradients, local plasticity and dislocation pile-up to DDC initiation in additively manufactured components.

Ductility-Dip Cracking Mechanisms in Nickel-Based Alloys publication trend

The graph below shows the total number of articles in ductility-dip cracking mechanisms in nickel-based alloys across all publications each year (not limited to Nature Index journals).

Technical terms

Ductility-dip temperature range: The narrow interval below the solidus where alloy ductility sharply decreases, promoting intergranular cracking.

Geometrically necessary dislocations (GNDs): Dislocations required to accommodate non-uniform plastic deformation and lattice curvature, often accumulating at grain boundaries.

High-temperature brittleness range (HTBR): The temperature span in which partial melting and reduced ductility coincide, leading to hot cracking susceptibility.

Coincidence-site lattice (CSL): A measure of grain boundary misorientation where certain boundaries exhibit lower energy and different resistance to sliding or cracking.

Transvarestraint test: A laboratory method applying controlled bending and thermal cycles to quantify hot-cracking criteria in weld metals.

References

1. Statistical study of ductility-dip cracking induced plastic deformation in polycrystalline laser 3D printed Ni-based superalloy. Scientific Reports (2017).
2. The Phenomena and Criteria Determining the Cracking Susceptibility of Repair Padding Welds of the Inconel 713C Nickel Alloy. Materials (2022).
3. Analysis of the ductility dip cracking in the nickel-base alloy 617mod. IOP Conference Series Materials Science and Engineering (2017).
4. Effect of Inconel 718 Filler on the Microstructure and Mechanical Properties of Inconel 690 Joint by Ultrasonic Frequency Pulse Assisted TIG Welding. Materials (2024).