ABSTRACT
The additive manufacturing (AM) technique, laser metal deposition (LMD), combines the advantages of near net shape manufacturing, tailored thermal process conditions and in situ alloy modification. This makes LMD a promising approach for the processing of advanced materials, such as intermetallics. Additionally, LMD allows the composition of a powder blend to be modified in situ. Hence, alloying and material build-up can be achieved simultaneously. Within this contribution, AM processing of the promising high-temperature material ß-NiAl, by means of LMD, with elemental powder blends, as well as with pre-alloyed powders, was presented. The investigations showed that by applying a preheating temperature of 1100 °C, ß-NiAl could be processed without cracking. Additionally, by using pre-alloyed, as well as elemental powders, a single phase ß-NiAl microstructure can be achieved in multi-layer build-ups. Major differences between the approaches were found within substrate near regions. For in situ alloying of Ni and Al, these regions are characterized by an inhomogeneous elemental distribution in a layerwise manner. However, due to the remelting of preceding layers during deposition, a homogenization can be observed, leading to a single-phase structure. This shows the potential of high temperature preheating and in situ alloying to push the development of new high temperature materials for AM.
ABSTRACT
Recently, additive manufacturing (AM) by laser metal deposition (LMD) has become a key technology for fabricating highly complex parts without any support structures. Compared to the well-known powder bed fusion process, LMD enhances manufacturing possibilities to overcome AM-specific challenges such as process inherent porosity, minor build rates, and limited part size. Moreover, the advantages aforementioned combined with conventional machining enable novel manufacturing approaches in various fields of applications. Within this contribution, the additive manufacturing of filigree flexure pivots using 316L-Si by means of LMD with powder is presented. Frictionless flexure pivot bearings are used in space mechanisms that require high reliability, accuracy, and technical cleanliness. As a contribution to part qualification, the manufacturing process, powder material, and fabricated specimens were investigated in a comprehensive manner. Due to its major impact on the process, the chemical powder composition was characterized in detail by energy dispersive X-ray spectroscopy (EDX) and inductively coupled plasma optical emission spectrometry (ICP-OES). Moreover, a profound characterization of the powder morphology and flowability was carried out using scanning electron microscopy (SEM) and novel rheological investigation techniques. Furthermore, quantitative image analysis, mechanical testing, laser scanning microscopy, and 3D shape measurement of manufactured specimens were conducted. As a result, the gained knowledge was applied for the AM-specific redesign of the flexure pivot. Finally, a qualified flexure pivot has been manufactured in a hybrid manner to subsequently ensure its long-term durability in a lifetime test bench.
