Even though the buildup rate of laser powder bed fusion processes (LPBF) has steadily increased in recent years by using more and more powerful laser systems, the production of large-volume parts is still extremely cost-intensive. Joining of an additively manufactured complex part to a high-volume part made of conventional material is a promising technology to enhance economics. Today, constructors have to select the most economical joining process with respect to the individual field of application. The aim of this research was to investigate the hybrid joint properties of LBPF and conventionally casted 18MAR300 nickel maraging steel depending on the manufacturing process and the heat treatment condition. Therefore, the microstructure and the strength of the hybrid joints manufactured by LPBF or vacuum brazing were examined and compared to solid material and joints of similar material. It was found that the vacuum-brazed hybrid joints using a 50.8-μm-thick AuNi18 foil provide a high tensile strength of 904 MPa which is sufficient for a broad field of application. Furthermore, the additively manufactured hybrid samples offered with 1998 MPa a tensile strength more than twice as high but showed a considerable impact of buildup failures to the strength in general.
The pseudoelasticity of NiTi shape memory alloys is a unique material property which can be characterized by a complete recovery of a previously impressed component shape by a change of the thermal or mechanical load conditions after deforming. In contrast to the elastic deformation of ordinary materials like steels, twentyfold higher elastic strain rates up to 10 % are possible due to a temperature or a stress induced diffusion-free transformation of the crystal lattice between the austenite and martensite phases. Therefore, these superelastic alloys are frequently used as actuators, implants or stents so that there is an extraordinary high requirement of reliability and biocompatibility. In terms of joining, vacuum brazing might be a particularly suitable method to produce joined components which preserve a maximum of pseudoelasticity. Within the present research, it was shown that the vacuum brazing process at 1180 °C using pure niobium is well integrable into a solution annealing and a shape annealing heat treatment in a single furnace run. This led to a distinct tension plateau at around 285 MPa with an almost R-phase-free conversion of NiTi. Furthermore, it was proven that the share of the superelastic and proeutectic NiTiNb-phase was significantly increased with the dwell time.
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