On the influence of alloy composition on the additive manufacturability of Ni-based superalloys

TL;DR

This study investigates how alloy composition affects the ease of additive manufacturing of Ni-based superalloys, revealing the relationship between composition, defect formation, and processability through experimental and modeling approaches.

Contribution

It introduces a comprehensive analysis linking alloy composition to defect susceptibility and proposes new models for solid-state and solidification cracking in additive manufacturing.

Findings

Alloy composition strongly influences defect formation during additive manufacturing.

A new model for solid-state cracking based on thermal stress relaxation is developed.

Modified solidification cracking criterion incorporating stress relaxation effects is proposed.

Abstract

The susceptibility of nickel-based superalloys to processing-induced crack formation during laser powder-bed additive manufacturing is studied. Twelve different alloys -- some of existing (heritage) type but also other newly-designed ones -- are considered. A strong inter-dependence of alloy composition and processability is demonstrated. Stereological procedures are developed to enable the two dominant defect types found -- solidification cracks and solid-state ductility dip cracks -- to be distinguished and quantified. Differential scanning calorimetry, creep stress relaxation tests at 1000$^\circ$C and measurements of tensile ductility at 800$^\circ$C are used to interpret the effects of alloy composition. A model for solid-state cracking is proposed, based on an incapacity to relax the thermal stress arising from constrained differential thermal contraction; its development is supported by experimental measurements using a constrained bar cooling test. A modified solidification cracking criterion is proposed based upon solidification range but including also a contribution from the stress relaxation effect. This work provides fundamental insights into the role of composition on the additive manufacturability of these materials.