Reducing solidification cracks and enhancing mechanical performance in additively manufactured Cu-Ti alloys via chemical fluctuation manipulation

Abstract

Additive manufacturing offers substantial design freedom for developing copper (Cu) alloy components with complex shapes. However, the extreme process conditions of this technique increase the risk of solidification cracking. Cu-titanium (Ti) alloy, a high-strength Cu alloy, exhibited solidification cracks due to the Ti segregation at grain boundaries when processed with laser powder bed fusion, reducing the appeal of Cu-Ti alloys in the additively manufactured Cu market. In this study, we incorporated chemical fluctuations via in-situ alloying in laser powder bed fusion to suppress solidification cracks. These fluctuations promote the transformation from coarse columnar grains to fine near-equiaxed grains, thereby mitigating solidification cracks at grain boundaries. Furthermore, we discovered that the degree of chemical inhomogeneity decreased with reducing the elemental powder size of in-situ alloying. Utilising this novel strategy, we successfully in-situ synthesised Cu-Ti alloys devoid of solidification cracks and strengthened by cellular microstructures. Compared to Cu-Ti alloys without chemical fluctuations fabricated using pre-alloyed powders, in-situ synthesised Cu-Ti alloys exhibited significantly boosted tensile strength (from 306.3 MPa to 534.7 MPa) and fracture elongation (from 1.8% to 18.4%). This study presents a practical methodology to address the challenge of solidification cracking in some additively manufactured Cu alloys.