Cracks Analysis of Graded Structural Material Fabricated by Hybrid Additive and Subtractive Manufacturing

Graded structural materials (GSMs) with variable performance and composition have a full application in the aerospace industry. Hybrid additive and subtractive manufacturing is very convenient to fabricate GSM by adjusting the composition of the deposited materials, removing the excess parts and improving the overall dimensions. Crack is a very significant defect in blocky GSM components because of the excessive heat accumulation and uneven distribution of residual stress. To analyze the reason and effects of cracks, blocky and thin-walled GSMs were fabricated. By analyzing the crack morphology, microstructures, element distribution and oxidation, results show that IN718 had much better oxidation resistance than 316L, which led to cracks appearing on the side of 316L. By adjusting the blocky structures to thin-walled structures, huge cracks almost disappeared. However, the poor bonding strength of the interface resulted in worse tensile strength of GSM than single 316L or IN718 by laser depositing.