Effect of composition and phase diagram features on printability and microstructure in laser powder bed fusion: Development and comparison of processing maps across alloy systems

Abstract

Additive manufacturing (AM) has gained considerable academic and industrial interest due to its ability to produce parts with complex geometries with the potential for local microstructural control. However, due to the large number of material and process variables associated with AM, optimization of alloying compositions and process parameters to achieve desired properties is an arduous task. There is a fundamental gap in understanding how changes in process variables and alloy composition and thermodynamics affect additively manufactured parts. The present systematic study sheds light on the effects of alloying composition and corresponding phase diagram features on the printability and solidification microstructures of four binary nickel-based alloys, namely, Ni-20 at% Cu, Ni-5 at% Al, Ni-5 at% Zr, and Ni-8.8 at% Zr. These compositions are selected to represent binary isomorphous, weak solute partitioning, strong solute partitioning, and eutectic alloying conditions, respectively. Single track and bulk experiments are conducted to quantify the effects of varying material thermodynamic properties such as solidification temperature ranges, alloy melting temperatures, and other solidification conditions on resultant microstructures across the laser powder bed fusion (L-PBF) parameter space. A simple framework for developing processing maps detailing porosity formation and microsegregation across the laser power – scan speed parameter space is established and validated for each of these alloys to determine how material properties affect printability and microstructure in L-PBF. This knowledge will be vital in optimizing alloy chemistry and process parameters to design alloys specifically for additive manufacturing, as well as to provide a path toward local microstructure control.