Electron Microscopy Analysis of 17-4 PH Powder for Additive Manufacturing
Metal additive manufacturing (MAM) has evolved into a production-ready manufacturing technology over a period of just a few years. The strong interest in MAM mainly derives from the ability to manufacture complex parts without the tooling and material waste typically associated with machining components from bulk alloys. Most of the attention for MAM has focused on Ti-6Al-4V and IN718 alloys, but several other alloy classes, such as stainless steels have gained traction as well. The stainless steels that have been considered for MAM include: 304, 316, and 17-4PH alloys, but to date none of these has been studied in great detail. 17-4PH is a heat-treatable martensitic stainless steel. Since MAM starts with the spreading or feeding of powders, a careful characterization of the starting powder is necessary to understand the way in which the microstructure and defects develop in the additively manufactured components, and how these lead to variations in component properties.
Non-metallic inclusions in 17-4PH stainless steel parts produced by selective laser melting
Abstract The character, morphology and distribution of inclusions has been studied in additively manufactured 17-4PH stainless steel parts produced from gas-atomized powder by selective laser melting. A combination of advanced electron microscopy techniques has been used to show that such parts contain oxide inclusions ranging from a few nm to tens of μm across. The coarser inclusions have morphologies that mimic the oxides which accumulate between melt tracks at the build surface, suggesting that these inclusions are incorporated into the build during deposition of subsequent layers. Such features could have deleterious anisotropic effects upon the fatigue and fracture resistance of the built parts. The finer inclusions are equi-axed, reside preferentially at grain boundaries, and could inhibit grain growth during processing via Zener pinning effects. The chemistries of the inclusions include elements such as Al that are not part of the alloy specification. This indicates that the inclusions are exogenous defects that are entrained in the melt during gas atomization due to interactions with the crucible or nozzle materials. Examples of encapsulated oxide material in the powder feedstock support this explanation. These observations highlight the need for careful control of powder pedigree when using additive manufacturing for critical structural components.
A device for uranium series leaching from glass fiber in HEPA filter
For the disposal of a high efficiency particulate air (HEPA) glass filter into the environment, the glass fiber should be leached to lower its radioactive concentration to the clearance level. To derive an optimum method for the removal of uranium series from a HEPA glass fiber, five methods were applied in this study. That is, chemical leaching by a 4.0 M HNO3–0.1 M Ce(IV) solution, chemical leaching by a 5 wt% NaOH solution, chemical leaching by a 0.5 M H2O2–1.0 M Na2CO3 solution, chemical consecutive chemical leaching by a 4.0 M HNO3 solution, and repeated chemical leaching by a 4.0 M HNO3 solution were used to remove the uranium series. The residual radioactivity concentrations of 238U, 235U, 226Ra, and 234Th in glass after leaching for 5 h by the 4.0 M HNO3–0.1 M Ce(IV) solution were 2.1, 0.3, 1.1, and 1.2 Bq/g. The residual radioactivity concentrations of 238U, 235U, 226Ra, and 234Th in glass after leaching for 36 h by 4.0 M HNO3–0.1 M Ce(IV) solution were 76.9, 3.4, 63.7, and 71.9 Bq/g. The residual radioactivity concentrations of 238U, 235U, 226Ra, and 234Th in glass after leaching for 8 h by a 0.5 M H2O2–1.0 M Na2CO3 solution were 8.9, 0.0, 1.91, and 6.4 Bq/g. The residual radioactivity concentrations of 238U, 235U, 226Ra, and 234Th in glass after consecutive leaching for 8 h by the 4.0 M HNO3 solution were 2.08, 0.12, 1.55, and 2.0 Bq/g. The residual radioactivity concentrations of 238U, 235U, 226Ra, and 234Th in glass after three repetitions of leaching for 3 h by the 4.0 M HNO3 solution were 0.02, 0.02, 0.29, and 0.26 Bq/g. Meanwhile, the removal efficiencies of 238U, 235U, 226Ra, and 234Th from the waste solution after its precipitation–filtration treatment with NaOH and alum for reuse of the 4.0 M HNO3 waste solution were 100, 100, 93.3, and 100%.