Selective laser melting of nano TiC-reinforced 18Ni300 Maraging steel for injection moulding applications

• Autor(a) principal: Leite, Francisco Fernandes
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/39730
• topic: Additive manufacturing; Selective laser melting; Maraging steel; Nanocomposites; Heat treatment

The use of additive manufacturing technologies has gained relevance among the most varied industries in the world in the last years. The moulding industry, one of the most relevant in Portugal, mainly uses conventional techniques. However, Simoldes Group, the main mould supplier in Europe, has tried to adopt and implement additive manufacturing technologies, namely Selective Laser Melting (SLM), in their production chain. In this work, 18Ni300 Maraging steel reinforced with TiC nanoparticles was produced using SLM aiming to optimize the fabrication of this nanocomposite. Design of Experiments (DoE) was used to generate twenty-five experimental groups, in which laser power, scanning speed, and hatch distance were varied amongst five levels. The effect of post-SLM fabrication aging treatment was also analysed. The powders' particle size distribution, morphology, and flowability were analysed to confirm the quality of the nanocomposite feedstock. After SLM fabrication, phase analysis, densification assessment, mechanical characterization, and thermal conductivity were studied. Results showed that the addition of TiC nanoparticles to 18Ni300 steel, although increasing the flow rate when compared to 18Ni300, led to a Compressibility Index and Hausner Ratio that classifies this feedstock as having Excellent Flowability. Martensite, austenite, and TiC were detected for as-built and heat-treated conditions of the nanocomposite. Densification analysis showed experiments with densification above 99.5%. It was concluded that experiment 10 gathers the best combination of micro-hardness and microstructural results, corresponding to a set of parameters of 200 W of laser power, 1500 mm/s of scanning speed, and 65 µm of hatch distance. Regarding mechanical characterization, in which the micro-hardness of the nanocomposites was measured, the as-built condition showed micro-hardness between 357 and 418 HV₂, whereas the heat-treated increased and varied between 632 and 673 HV₂. Regarding the heat-treated condition, the most suited for Maraging steels, 18Ni300+TiC revealed a thermal conductivity very similar to the heat-treated non-reinforced 18Ni300, while exhibiting higher hardness than the non-reinforced Maraging steel, allowing to conclude that the addition of TiC can be effective for obtaining an efficient compromise between thermal and mechanical performance for injection moulding applications.