Quality Diagnostics of Parts Produced by Combined Additive Manufacturing Technology

The work is focused on the combined process of obtaining bimetallic parts that involve laser-directed energy deposition (LDED) additive technology and the conventional casting process. In this research, molybdenum powder was deposited by LDED on a cast 25L steel substrate. The choice of materials is motivated by demands for replacing the traditional technique of brazing molybdenum with a copper interlayer on low-carbon steel to eliminate shortcomings. The influence of powder particle morphology on the quality of deposited layers was studied. Spherical molybdenum powder PMS-M99.9 facilitated stable deposition of good layers and was found to be suitable for the LDED. Quality diagnostics were performed by studying microstructure, hardness, and wear resistance properties. Preferential parameters of the LDED of molybdenum were found through parametrical analysis. Microstructural studies showed that LDED of PMS-M99.9 powder results in a homogeneous stable layer with a strong bond to the steel substrate, which was confirmed by mutual diffusion of Mo and Fe in the boundary. It is also demonstrated that the found working parameters of LDED assure high hardness, wear, and fretting wear resistance. The three studied coatings (LDED of powders PMS-M99.9 and PM-M; VM1 brazing) had the same friction coefficient value of ~0.25. Compared to others, PMS-M99.9 coating had the lowest volumetric wear, while abrasive wear was measured to be the highest.