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Direct aging heat treatment recipes were developed for additively manufactured (AM) PH13–8Mo stainless steel by studying the kinetics of precipitation phase transformation in the as-built material. The samples were printed using two AM processes; i.e., arc-directed energy deposition (arc-DED) and laser-powder bed fusion (L-PBF) techniques. The as-built samples were characterized using differential scanning calorimetry (DSC) to determine the characteristics of precipitation phase transformation. Due to different thermal histories during the arc-DED and L-PBF processes, the resulting microstructures and physical properties were different; therefore, the precipitation kinetics were different. The kinetics results were used to design a direct aging heat treatment to promote the formation of β-NiAl precipitates. Two different heat treatment recipes were designed considering the differences between the two materials. Direct aging of arc-DED-PH13-8Mo resulted in a concurrent improvement in strength and ductility, while direct aging of L-PBF-PH13-8Mo resulted in a significant increase in strength and retention of ductility. The microstructure was then correlated to the physical (i.e., the kinetics of precipitation) and mechanical (i.e., strength and ductility) properties. Concurrent strength and ductility improvement in the arc-DED-PH13-8Mo was controlled by the evolution of nano-scaled β-NiAl clusters. In the L-PBF-PH13-8Mo, the strength enhancement was governed by the evolution of nano-scaled β-NiAl precipitates, while the ductility retention was dictated by preserving the pre-existing dislocation networks.

A hydrogen reduction-based method for additive manufacturing of carbon steels from low cost and stable oxide powders is presented. This method uses materials extrusion processes to extrude inks composed of oxide powders, plastic binders, and solvents. Oxide powders are synthesized into viscous inks and extruded under ambient conditions into three-dimensional architectures. The three-dimensional printed green bodies are reduced at elevated temperatures in hydrogen-rich environments to burn off the polymer binder and reduce the oxide powders, yielding metal alloys with controlled compositions. While this approach has been demonstrated in previous publications for various alloys, the addition of carbon, an important element in most industrial steels, has been a persistent challenge. This paper demonstrates an approach to introduce carbon during the reduction process, resulting in through-thickness carburization of the final parts.

ABSTRACTMaterial extrusion additive manufacturing is of increased interest in producing materials with very high loadings of particles, specifically through the use of the direct ink write (DIW), or robocasting, technique and the use of highly loaded particle suspensions (HLS). Applications from biomedical composites to solid rocket propellants to powder metallurgy green bodies would benefit from the complex parts enabled by additive manufacturing but require very high particle contents during processing. This leads to very high viscosity fluids and challenges in flowing and curing the inks. In this comprehensive review, we examine the main components of designing an ink formulation and a DIW process: the ink rheology, the print mechanics and the solidification/post-processing. Our expanded discussion of these elements includes an introduction to the basics as well as the latest research in the field, so serves to both introduce a new practitioner and generate new ideas for those already working in the area. We finish with a discussion of two important applications and a perspective on the future directions of DIW for highly loaded particle materials.

Applying an electric field to an antiferroelectric material transforms its non-polar crystal structure into a polar one. Here, the authors show that the antiferroelectric transition in zirconia causes a negative capacitance, useful for electronics.

Abstract Al–Mg alloys undergo sensitization when exposed to elevated temperatures, making them susceptible to intergranular corrosion and stress corrosion cracking. Most of the existing research on microstructure effects on sensitization is centered on the effect of intrinsic grain boundary characteristics such as misorientation angle and coincident site lattice (CSL) values. Very few studies have systematically investigated the influence of extrinsic characteristics such as dislocation density. In this paper, the influence of local microstructure characteristics on the sensitization susceptibility of AA5456 was investigated using in situ optical microscopy corrosion experiments and electron back scattering diffraction analysis. The results show a clear trend between the local geometrically necessary dislocation (GND) density and β phase precipitation, with higher GND densities correlating with higher rates sensitized boundaries. This trend held true even for low angle grain boundaries. These results demonstrate the importance of considering factors beyond grain boundary characteristics in determining susceptibility to sensitization.