Experimental cooling rates during high-power laser powder bed fusion at varying processing conditions

Abstract

High-power laser power bed fusion (HP-LPBF) with a large flat-top laser beam allows additive manufacturing of components at much higher build-up rates than conventional LPBF, since thicker powder layers can be processed. This makes this technology attractive for industry due to the augmented productivity. Here, we have utilized HP-LPBF to fabricate Al-33Cu (wt%) specimens at differing layer thickness and laser power. Based on the average spacing of the lamellae of the eutectic microstructure, the cooling rate inherent to HP-LPBF was experimentally determined as a function of the processing conditions. At the lowest layer thickness (50 µm) and laser power (500 W), the cooling rate amounts to about 90000 K/s, whereas it drops to about 15000 K/s for HP-LPBF with the largest layer thickness (200 µm) and highest laser power (1000 W). When the base plate is additionally pre-heated, the cooling rate prevailing during solidification decreased to about 5000 K/s. Our findings demonstrate that relatively low cooling rates are effective during HP-LPBF at high build-up rates being tantamount to high productivity. It should be considered that such drastic changes in cooling rate may strongly affect the microstructure formation, the properties and hence performance of the corresponding additively manufactured component.