Effect of Zr content on crack formation and mechanical properties of IN738LC processed by selective laser melting

Two batches of commercial IN738LC alloy powders with different Zr contents were printed under the same parameters. The influences of Zr content (0.024 wt.% and 0.12 wt.%, respectively) in powders on crack density, distribution, formation mechanism and mechanical properties of selective laser melting (SLM)-treated parts were systematically studied. It was found that the crack density (area ratio) increases from 0.15% to 0.87% in the XOY plane and from 0.21% to 1.81% in the XOZ plane along with the Zr content increase from 0.024 wt.% to 0.12 wt.% in the original powders. Solidification cracks are formed along the epitaxially grown 〈001〉-oriented columnar grain boundaries in molten pool center. The ultimate tensile strength of Sample 1 (0.024 wt.% Zr) is 1113 MPa, and there are dimples in tensile fracture. With an increase in the Zr content to 0.12 wt.% (Sample 2), the ultimate tensile strength of Sample 2 decreases to 610 MPa, and there are numerous original cracks and exposed columnar grain boundaries in tensile fracture. The optimization of printing parameters of Sample 2 considerably increases the ultimate tensile strength by 55.2% to 947 MPa, and the plasticity is greatly improved.