Details

This work is a first approach to investigate the influence of powder microstructure on the mechanical and microstructural properties of parts produced by Directed Energy Deposition (DED), a metal additive manufacturing process. The study focuses on two engineering alloys, 316L stainless steel and H13 tool steel. The main goal was to determine whether thermally altering the internal structure of the powder before printing has a measurable effect on the mechanical and microstructural characteristics of the final parts. The specific objectives included analysing the untreated and thermally treated powders, producing samples under identical DED conditions, applying post-deposition heat treatment to the H13 specimens, and evaluating porosity, hardness, tensile strength, and microstructure in all samples. The methodology combined experimental fabrication with advanced characterisation techniques. The powders were examined using scanning electron microscopy and energy dispersive spectroscopy to assess morphology and chemical composition. Samples were then produced using DED. After printing, the H13 samples underwent a conventional heat treatment. Mechanical testing included Vickers hardness and uniaxial tensile testing, while microstructural analysis was carried out using optical microscopy, SEM with backscattered imaging, and elemental mapping. The results showed that 316L parts were not significantly affected by powder treatment. Both strength and hardness remained within typical values reported in the literature. A small decrease in elongation was observed in the samples made from thermally treated powder, but no major difference in performance was recorded. In contrast, H13 showed a more pronounced response. As-printed samples made from thermally treated H13 powder had lower strength and reduced ductility compared to those made from untreated powder. Ultimate tensile strength dropped by approximately 33 percent. However, after quenching and tempering, the differences between the two groups were minimal. This suggests that the post-processing heat treatment reset the microstructure and removed any influence from the initial powder condition. The microstructural analysis confirmed that the carbides formed during powder annealing were not preserved in the final parts, most likely due to full dissolution during melting. Submicron pores and chemical uniformity were observed, but no retained features from the original powder microstructure were identified. This study contributes to the understanding of how powder microstructure affects DED part quality. The findings show that, although the powder condition can influence as-built properties, especially in H13, these effects are largely removed by standard post-processing treatments. The results are relevant to additive manufacturing processes where powder reuse or conditioning is considered. Future work should focus on reducing variability within powder batches, increasing the number of test samples for statistical confidence, and exploring methods to better control microstructural evolution during printing. This research serves as a foundation for deeper studies into powder behaviour and process control in metal additive manufacturing.

• INTRODUCTION
• CHAPTER 1 LITERATURE REVIEW
  • 1.1​Overview of Additive Manufacturing Technologies
  • 1.1.1​​Key Principles of Powder Additive Manufacturing
  • 1.1.2​​Comparison of Different Powder AM Techniques
  • 1.1.3​Direct Energy Deposition
  • 1.2​Microstructure of metals
  • 1.2.1​Influence on macroscopic properties
  • 1.2.2​Tailoring methods
  • 1.3​Alloy 316L
  • 1.4​Alloy H13
• CHAPTER 2 METHODOLOGY
  • 2.1 Raw material powder
  • 2.2 DED printing
  • 2.3 Post-processing
  • 2.4 Testing
  • 2.4.1 Tensile Testing
  • 2.4.2 Porosity Evaluation
  • 2.4.3 Vickers Hardness Testing
  • 2.4.4 ​Microscopic and metallographic analysis
• CHAPTER 3 RESULTS AND DISCUSSION
  • 3.1​Porosity
  • 3.2​Hardness
  • 3.3​Tensile Strength
  • 3.4​Microstructure
  • 3.4.1​H13 untreated
  • 3.4.2​H13 with annealing treatment
  • 3.4.3​DED printed microstructure
• CONCLUSIONS
• REFERENCES