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


A graph showing the alloys plotted against cracking ductility and flow stress at 800 degrees celsius

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.