Surface chemistry in Ti-6Al-4V feedstock as influenced by powder reuse in electron beam additive manufacturing.

X-ray photoelectron spectroscopy (XPS) as well as scanning and transmission electron microscopy (SEM/TEM) analysis was carried out on four Ti-6Al-4V powders used in electron beam powder-bed fusion (PBF-EB) production environments: virgin low oxygen (0.080 wt% O), reused medium oxygen (0.140 wt% O), reused high oxygen (0.

Elastic-plastic properties of mesoscale electrodeposited LIGA nickel alloy films: microscopy and mechanics.

The elastic-plastic properties of mesoscale electrodeposited LIGA Ni alloy specimens are investigated as a function of specimen size, strain rate, and material composition. Two material compositions are studied: a high-strength fine-grained Ni-Fe alloy and a high-ductility coarse-grained Ni-Co alloy. The specimens have thicknesses of approximately 200 m and gauge widths ranging from 75 m to 700 m.

Microfabricated fiducial markers for digital image correlation-based micromechanical testing of LIGA Ni alloys.

Photolithographically defined thin film Au dots were used as micro fiducial markers for digital image correlation (DIC), to enable two-dimensional strain measurement of 200 m-thick LIGA (Lithographie, Galvanformung, Abformung) nickel alloys. Due to the sensitivity of electrodeposited films' microstructure and properties on the processing conditions, characterization of LIGA mechanical properties continues to be necessary for microsystems commercialization. DIC offers advantages over laser-based strain measurement techniques but creating suitable speckle patterns on specimens with dimensions under a millimeter is challenging.

Dominant factors for fracture at the micro-scale in electrodeposited nickel alloys.

Two different LIGA electrodeposited nickel alloys displayed distinct fracture modes after meso-scale tensile testing. The Ni-Co alloy failed in a ductile manner, while the Ni-Fe alloy failed in a more brittle-appearing manner. Various factors affecting the fracture are discussed; it was determined that the fracture mode did not depend upon the strain rate but did depend upon the sample geometry.

Hydrogen embrittlement in ferritic steels.

Hydrogen will be a crucial pillar in the clean-energy foundation, and therefore, the development of safe and cost-effective storage and transportation methods is essential to its success. One of the key challenges in the development of such storage and transportation methods is related to the interaction of hydrogen with structural materials. Despite extensive work, there are significant questions related to the hydrogen embrittlement of ferritic steels due to challenges associated with these steels, coupled with the difficulties with gauging the hydrogen content in all materials.

Fatigue Testing of Pipeline Welds and Heat-Affected Zones in Pressurized Hydrogen Gas.

Several welds and associated heat-affected zones (HAZs) on two API X70 and two API X52 pipes were tested to determine the fatigue crack growth rate (FCGR) in pressurized hydrogen gas and assess the area of the pipe that was most susceptible to fatigue when subjected to hydrogen gas. The relationship between FCGRs for welds and HAZs compared to base metal is discussed relative to local residual stresses, differences in the actual path of the crack, and hydrogen pressure effects.