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- Title
ON THE MEASUREMENT OF MOISTURE CONTENT IN METAL POWDERS BY KARL FISCHER TITRATION AND EFFECTS OF MOISTURE ADSORPTION ON DYNAMIC FLOW BEHAVIOR FOR ADDITIVE MANUFACTURING.
- Authors
van der Wiel, David; Pawlak, Ethan; Gutzky, Tyler
- Abstract
The moisture content and flowability of metal powders used in powder-bed based additive manufacturing processes are both critical properties for successful and controllable AM part production. The interconnectivity of these two properties can vary from subtle to significant, depending on alloy type, initial state, recycled powder content, and ambient atmospheres. There are currently no standard test methods specific to metal powders for measuring moisture content or for characterizing their dynamic flow behavior. In this study, the use of Karl Fischer titration in combination with oven desorption was examined for measuring ppm-level moisture content in seven common alloy powders in various states. Avalanche (or drum) rheometry was then used to quantify the flow behavior of dried and hydrated powders. Coulometric Karl Fisher titration was shown to provide repeatable results at moisture levels as low as about 20 ppm. Upon exposure to 50% relative humidity, the powders adsorbed moisture to varying degrees, but all exhibited decreased apparent flowability according to one or more of the dynamic rheometer parameters. The diminished flowability was shown to be dependent not on absolute water content, but the powders' relative moisture uptake, which is a function of the material type (and thus native surface oxide). A Ni-625 powder exhibited the highest sensitivity to moisture, while a Ti-6Al-4V powder exhibited the lowest sensitivity.
- Subjects
KARL Fischer technique; ELECTRON beam furnaces; METAL powders; MOISTURE measurement; ALLOY powders; MOISTURE; MANUFACTURING processes
- Publication
International Journal of Powder Metallurgy, 2022, Vol 58, Issue 2, p43
- ISSN
0888-7462
- Publication type
Article