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 β-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, β-NiAl could be processed without cracking. Additionally, by using pre-alloyed, as well as elemental powders, a single phase β-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.
Highlights
Sample characterization and analysis were conducted by Light Optical Microscope (LOM), Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) and XRD analysis
Low ductility and fracture toughness at room temperature as well as limited high temperature strength in a binary state have prevented its transfer into industrial applications so far
Pre-alloyed Ni50Al50 as well as elemental Ni and Al powders were processed by laser metal deposition (LMD) in order to additively manufacture single phase β-NiAl structures
Summary
Within the last few decades, aero engines have been steadily developed in order to increase efficiency and fulfil required maintenance intervals. The unsolved issues of limited ductility and fracture toughness at room temperature, as well as a poor strength at high temperatures, have prevented its transfer to industry so far [2,3]. The limited ductility and poor fracture toughness of β-NiAl are caused by its cubic B2 structure, exhibiting only three independent slip systems at room temperature and not fulfilling von Mises criterion [8]. Overcoming these challenges using manufacturing and alloying technology could yield a tremendous mass reduction of turbine rotors of up to 40% [8]
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