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.
Evaluation of Impact of Yarn Count and Stitch Length on Pilling, Abrasion, Shrinkage and Tightness Factor of 1 ? 1 Rib Cotton Knitted Fabrics
This study investigates the impact of yarn count and stitch length of 100% cotton knitted fabrics. 1 × 1 ribs structured fabrics were used in this research work. The stitch length 2.50 mm, 2.52 mm, 2.60 mm, 2.70 mm, 2.80 mm and 2.96 mm were used of the yarn count of 26Ne, 28Ne and 36Ne. The areal densities of the grey fabrics were in various amounts. The impacts of yarn count and stitch length were measured concerning pilling resistance, abrasion resistance, and shrinkage and tightness factor. The result showed that the fabric pilling grade decreased while number of cycle increased. Abrasion resistance decreased but length wise shrinkage increased despite the fact that the stitch length increased. The results also exposed that the tightness factor of the fabric increased with the increase of the stitch length in both dyeing and washing state and finished state compared to grey state for the yarn count 26Ne and homogeneous result not found for yarn count 28Ne and 36 Ne. Evaluation of Impact of Yarn Count and Stitch Length on Pilling, Abrasion, Shrinkage and Tightness Factor of 1 × 1 Rib Cotton Knitted Fabrics