Porosity is an inherent attribute in selective laser melting (SLM) and profoundly degrades the build part quality and its performance. This study attempts to understand and characterize the keyhole pores formed during single-track scanning in SLM. First, 24 single tracks were generated using different line energy density (LED) levels, ranging from 0.1 J/mm to 0.98 J/mm, by varying the laser power and the scanning speed. The samples were then scanned by micro-computed tomography to measure keyhole pores and analyze the pore characteristics. The results show a general trend that the severity of the keyhole porosity increases with the increase of the LED with exceptions of certain patterns, implying important individual contributions from the parameters. Next, by keeping the LED constant in another set of experiments, different combinations of the power and the speed were tested to investigate the individual effect. Based on the results obtained, the laser power appears to have a greater effect than the scanning speed on both the pore number and the pore volume as well as the pore depth. For the same LED, the pore number and volume increase with increasing laser power until a certain critical level, beyond which, both the pore number and volume will decrease, if the power is further increased. For the LED of 0.32 J/mm, 0.4 J/mm, and 0.48 J/mm, the critical laser power that reverses the trend is about 132 W, 140 W, and 144 W, respectively.

In this study, micro-computed tomography (CT) is utilized to detect defects of Ti-6Al-4V specimens fabricated by selective laser melting (SLM) and electron beam melting (EBM), which are two popular metal additive manufacturing methods. SLM and EBM specimens were fabricated with random defects at a specific porosity. The capability of micro-CT to evaluate inclusion defects in the SLM and EBM specimens is discussed. The porosity of EBM specimens was analyzed through image processing of CT single slices. An empirical method is also proposed to estimate the porosity of reconstructed models of the CT scan.

Titanium dioxide <mml:math display="inline"><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mi>TiO</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow></mml:math>(TiO2) photocatalytic films can be excited only by UV light which is about 4–5% of the overall solar spectrum and the activity under visible light irradiation is very limited. In this study, atomic layer deposition was used to deposit <mml:math display="inline"><mml:mrow><mml:msub><mml:mi>ZrO</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>ZrO2 -doped <mml:math display="inline"><mml:mrow><mml:msub><mml:mi>TiO</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>TiO2 films which had better visible light response. X-ray diffraction, electron microscopy and Raman, X-ray photoelectron, and UV-visible spectroscopy were used to characterize the films. The photocatalytic activities were measured by decomposition of stearic acid coating. <mml:math display="inline"><mml:mrow><mml:msub><mml:mi>ZrO</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>ZrO2 -doped <mml:math display="inline"><mml:mrow><mml:msub><mml:mi>TiO</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>TiO2 retained the anatase crystal phase when zirconium substitution was below 10%. The doped film with 9:1 <mml:math display="inline"><mml:mrow><mml:mi>Ti</mml:mi><mml:mo>:</mml:mo><mml:mi>Zr</mml:mi></mml:mrow></mml:math>Ti:Zr pulse ratio has greater visible light absorption and a bandgap reduction of <mml:math display="inline"><mml:mrow><mml:mn>0.2</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi>eV</mml:mi></mml:mrow></mml:math>0.2eV . The photocatalytic decomposition efficiency under visible light irradiation was increased by 50% compared to undoped <mml:math display="inline"><mml:mrow><mml:msub><mml:mi>TiO</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>TiO2 .