In-situ X-ray microtomography of interface between additively manufactured aluminium bronze and H13 tool steel

Abstract

Directed energy deposition (DED) is an additive manufacturing process category where material is melted as it is deposited, often powder melted with a focused laser. In this work aluminium bronze was deposited onto H13 tool steel using this technique, forming a mixing zone between the two metals. This mixing zone was examined with X-ray microtomography to obtain a three dimensional perspective that is unrealizable with conventional microscopy. Both the shape of the melt pools, the microstructure within, and processing defects could be discerned due to varying absorption of the radiation. In addition to characterizing the microstructure, the sample was also strained in three steps; the first step was to approximately 2.5 % strain, the second to 10.5 % and finally until fracture of the sample. The sample was scanned between each step, including a scan of the fracture surface. The ultimate tensile strength was found to be approximately 850 MPa and the fracture was observed to originate from cracks between the H13 substrate and the mixing zone. These cracks appeared to form in the second step of the straining. Additionally, local strains were estimated by utilizing pores in the sample as tracking points.