Researchers from this department, Engineering and Alloyed Limited worked together to produce this paper, 'On the influence of alloy composition on the additive manufacturability of Ni-based superalloys', published in Metallurgical and Materials Transactions A.
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 oC and measurements of tensile ductility at 800oC 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 solidifcation 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.