Thermal gradients in binary Ni-Nb bulk metallic glass fabricated through Laser Powder Bed Fusion: Investigation on vitrification and residual stresses

• Applicants: Professor Dr. Ralf Busch; Dr.-Ing. Stefan Kleszczynski
• Subject Area: Materials in Sintering Processes and Generative Manufacturing Processes ; Synthesis and Properties of Functional Materials
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 564610000

Advanced materials such as bulk metallic glasses (BMGs) have outstanding mechanical properties. The amorphous atomic arrangement of BMGs leads to high strength values of 2-5 GPa with a simultaneously high elastic yield strength of around 2-3 %. The vitrification of a metallic melt into a glass-like structure requires good glass-forming ability (GFA) of the alloy and high cooling rates during the manufacturing process in order to prevent crystallization. In conventional manufacturing processes such as casting, cooling rates are inherently limited. This limits the manufacturable size of BMGs and excludes them from most engineering applications. Laser powder bed based metal melting (PBF-LB/M) has offered the possibility of producing large and complex structures from BMGs for several years. The interaction of laser and material enables cooling rates of up to 10^6 K/s, and the layer-by-layer process decouples the local cooling rate from the component size. However, cyclic reheating, oxygen absorption and cracking behavior still pose technological challenges. Based on the limited knowledge of laser-material interaction, “strong glass formers” such as Zr-based alloys are generally selected for the PBF-LB/M process. This results in a simple process design, but at the expense of only average strength (2 GPa) for BMGs. The BMGs successfully processed using PBF-LB/M today therefore have low critical cooling rates of 20-500 K/s, which can in principle be exceeded by four to five orders of magnitude using PBF-LB/M. The project aims to exploit the full potential of the highly dynamic laser-material interaction in PBF-LB/M. Therefore, the binary glass-forming alloy Ni62Nb38 will be considered as an example. This alloy has sufficient GFA for amorphous processing by PBF-LB/M and can achieve a flexural strength of up to 3.5 GPa. However, preliminary tests have identified the occurrence of residual stress-induced cracks during processing as a critical challenge. In this context, the interaction between the thermal history, the residual stresses that occur and the material properties must be investigated in more detail. For this purpose, the temperature gradients and the resulting deformation are analyzed in situ using ratio pyrometry and a novel strain measurement setup. Based on a comprehensive microstructural and mechanical characterization of the samples, thermal gradients will be functionalized for processing into dense and amorphous Ni62Nb38 specimens. The expected results will open up new avenues for the widespread use of BMGs in industrial applications.

• DFG Programme: Research Grants
• International Connection: Australia
• Co-Investigator: Dr.-Ing. Jan Wegner
• Cooperation Partner: Professor Dr. Jamie J. Kruzic