Date

2020-9-10

Author

Aydın, İbrahim

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18Ni300 maraging steel (MS300) has exceptional mechanical properties due to nanosize intermetallic precipitates in martensitic matrix. It is preferred for critical aircraft components that require high strength and toughness. Very low C-content leads to good weldability and thusit is an attractive candidate for additive manufacturing (AM) techniques. In recent years, production of maraging steel components via AM techniques instead of traditional processes has gained importance in aerospace industry due to easy production of complex geometries at one step together with reduction in production time, amount of scrap, and cost. To achieve the design requirements related to the mechanical properties and to eliminate the anisotropic material behavior, the as-built parts need optimized post-AM heat treatments. Moreover, establishing easy, rapid and reliable non-destructive measurement procedures for monitoring the variations in the microstructure and mechanical properties is a challenging issue. In this study, the effects of solution and aging treatments on the microstructure and mechanical properties of 18Ni300 maraging steel that was additively produced by the selective laser melting (SLM) method were investigated. Optical microscopy, scanning electron microscopy, x-ray diffraction, hardness test, tensile test, and ultrasound velocity measurements have been performed vi to characterize the specimens. The results show that as-built specimens consist of submicron dendritic cellular structures in the horizontal cross-section and elongated acicular structures in the vertical cross-section. Excess number of dislocations in the lath type bcc-martensite provides favorable nucleation sites for precipitates. After aging treatment, the hardness increased from 370 HV to nearly 610 HV due to precipitation of Ni3Ti, Ni3Mo and Fe2Mo. Meanwhile, the ultimate tensile strength increased from 1200 MPa up to 2100 MPa with a corresponding 60 percent reduction in the % elongation. There are correlations between ultrasonic wave velocity and some mechanical properties, such as elastic modulus and hardness. This makes the sound velocity measurement a potential tool for non-destructive characterization of the microstructure and mechanical properties and monitoring of their variations in the additively manufactured and heat-treated maraging steel components.

Subject Keywords

Maraging steel, Additive manufacturing, Selective laser melting, Heat treatment, Non-destructive material characterization, Sound velocity

URI

https://hdl.handle.net/11511/69042

Collections

Graduate School of Natural and Applied Sciences, Thesis