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.
Characterization of 17-4PH stainless steel powders produced by supersonic gas atomization
Abstract17-4PH stainless steel powders were prepared using a supersonic nozzle in a close-coupled gas atomization system. The characteristics of powder particles were carried out by means of a laser particle size analyzer, scanning electron microscopy (SEM), and the X-ray diffraction (XRD) technique. The results show that the mass median particle diameter is about 19.15 μm. Three main types of surface microstructures are observed in the powders: well-developed dendrite, cellular, and cellular dendrite structure. The XRD measurements show that, as the particle size decreases, the amount of fcc phase gradually decreases and that of bcc phase increases. The cooling rate is inversely related to the particle size, i.e., it decreases with an increase in particle size.
Rotational Analysis of the CrO Bands
The (0, 1), (0, 0) and (1, 0) bands of the CrO, which appear in the red and yellow region, are analysed rotationally, and we have been able to show that these bands owe to the transition 5 Π- 5 Π. We have shown the theoretical formulae for the quintet state, which can be applied in the case of nearly (a), and obtained the molecular constants as follows,