Introduction
Materials and Methods
Powder Properties
Fe | C | Mo | Ni | Mn | Cr | Si | O |
---|---|---|---|---|---|---|---|
Bal. | 0.015 | 2.5 | 12.7 | 1.5 | 16.9 | 0.7 | 0.059 |
Particle size | D10 | D50 | D90 |
---|---|---|---|
Average | 30.9 | 45.4 | 65.9 |
SD | 0.6 | 0.4 | 0.5 |
Specimen Manufacturing
Surface Roughness
Residual Stress
High Cycle Fatigue
Microstructure
Hardness and Porosity
Results and Discussion
Surface Roughness
Layer thickness, µm | As printed | Postmachined | ||||
---|---|---|---|---|---|---|
Sa, µm | Sq, µm | S10z, µm | Sa, µm | Sq, µm | S10z, µm | |
30 | 13.1 ± 0.8 | 15.9 ± 1.0 | 69.4 ± 11.7 | 0.5 | 0.7 | 5.0 ± 1.1 |
50 | 15 ± 2.0 | 18.5 ± 2.5 | 71.8 ± 5.3 | 0.5 | 0.7 ± 0.1 | 4.0 ± 0.4 |
Residual Stress
Microstructure
Hardness and Porosity
Layer thickness | Condition | Porosity, area% | Total Amount of Pores |
---|---|---|---|
30 | As printed | 0.1 | 97 |
30 | Postmachined | 0.03 | 30 |
50 | As printed | 0.27 | 270 |
50 | Postmachined | 0.23 | 207 |
Fatigue Tests
Fractography
Conclusions
- Increasing the layer thickness from 30 to 50 µm has a minor negative impact on fatigue strength; however, it has a major positive impact on the productivity of the SLM process. In both as-printed and postmachined conditions, the data suggest a slight increase in fatigue strength when using 30-µm layers.
- A significantly higher content of pores is found in samples manufactured with 50 µm layer thickness than in those fabricated with 30 µm.
- The impact of the postmachining operation on fatigue is far greater than that of the layer thickness.
- In the as-printed condition, fatigue strength suffers from high surface roughness, tensile surface residual stresses, and defects such as pores and lack of fusion.
- Improvement of fatigue strength after machining is due to lower surface roughness, the presence of compressive surface residual stresses, and removal of surface porosity.
- The fatigue strength of SLM-manufactured 316 L stainless steel in the as-printed condition seems to be slightly lower than that of conventionally produced 316 LN stainless steel material. However, after machining, the fatigue strength of SLM-produced parts is considerably higher than that of their conventionally produced counterparts.