Valence band study of thermoelectric Zintl-phase SrZn_2Sb_2 and YbZn_2Sb_2: X-ray photoelectron spectroscopy and density functional theory

The electronic structure of SrZn_2Sb_2 and YbZn_2Sb_2 is investigated using density functional theory and high-resolution x-ray photoemission spectroscopy. Both traditional Perdew-Burke-Ernzerhof and state-of-the-art hybrid Heyd-Scuseria-Ernzerhof functionals have been employed to highlight the importance of proper treatment of exchange-dependent Zn  3d states, Yb 4f states, and band gaps. The role of spin-orbit corrections in light of first-principles transport calculations are discussed and previous claims of Yb^(3+) valence are investigated with the assistance of photoelectron as well as scanning and transmission electron microscopy

Composition and structure of Pd nanoclusters in SiOx_x thin film

The nucleation, distribution, composition and structure of Pd nanocrystals in SiO$_2$ multilayers containing Ge, Si, and Pd are studied using High Resolution Transmission Electron Microscopy (HRTEM) and X-ray Photoelectron Spectroscopy (XPS), before and after heat treatment. The Pd nanocrystals in the as deposited sample seem to be capped by a layer of PdO$_x$. A 1-2 eV shift in binding energy was found for the Pd-3d XPS peak, due to initial state Pd to O charge transfer in this layer. The heat treatment results in a decomposition of PdO and Pd into pure Pd nanocrystals and SiO$_2$

Microstructure and Salt Fog Corrosion of Wrought Mg-Al-Zn and Mg-RE Alloys

Wrought magnesium alloys have received attention due to their potential application as lightweight materials. However, their use is limited by their poor corrosion resistance. Rare earth additions have the potential to enhance corrosion resistance. The present work included a microstructural investigation and corrosion testing of the alloy WE-43, containing Nd and Y, which was compared against the more conventional compositions of AZ31 and AZ61 alloys. All three alloys exhibited a recrystallized equiaxed structure after hot rolling with the presence of second phases—precipitates. The WE-43 alloy exhibited a better corrosion resistance than AZ31 and AZ61 under salt fog testing, indicated by the lower depth of attack and lower weight loss. The second phases in the microstructure of AZ31 and AZ61 alloys determined their corrosion resistance. The second phases in the AZ31 and AZ61 alloys (based on Al-Mg and Al-Mn phases) were nobler than the Mg matrix and catholically acted, thus sacrificing the Mg matrix. The superior corrosion resistance of WE43 was due to the incorporation of Y in the oxide/hydroxide film. In addition, the second phases in the WE43 consisted of Nd and Y and were less noble than the Mg-matrix. Thus, they acted as anodic sites protecting the Mg-matrix. The above results show the beneficial effect of rare earth additions to wrought Mg alloys towards increased corrosion resistance

Novel Powder Feedstock towards Microstructure Engineering in Laser Powder Bed Fusion: A Case Study on Duplex/Super Duplex and Austenitic Stainless-Steel Alloys

Additive manufacturing of Duplex Stainless Steels (DSS) and Super Duplex Stainless Steels (SDSS) has been successfully demonstrated using LPBF in recent years, however, both alloys feature an almost fully ferritic microstructure in the as-built condition due to the fast cooling rates associated with the Laser Powder Bed Fusion (LPBF) process. Blends of DSS and SDSS powders were formulated with austenitic stainless-steel 316L powder, aiming to achieve increased austenite formation during in the LPBF as-built condition to potentially minimize the post heat treatments (solution annealing and quenching). Powder characteristics were investigated and process parameters were optimized to produce near fully dense parts. Nanoindentation (NI) tests were conducted to measure, not only the local mechanical properties and correlate them with the as-built microstructure, but also to gain a deeper understanding in the deformation behavior of individual phases that cannot be studied directly by macroscopic tensile tests. Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD) were employed for microstructural analysis and phase quantification. The microstructural analysis and EBSD phase maps revealed an increase in austenite in the as-built microstructures. Blend 1 resulted in a duplex microstructure consisting of 10% austenite at the XY plane and 20% austenite at the XZ plane. The austenite content increased with increasing proportion of 316L stainless steel in the powder blends. The DSS blend required a much higher volumetric energy density for the fabrication of near fully dense parts. This imposed a slower solidification and a higher melt pool homogeneity, allowing for adequate diffusion of the austenite stabilizing elements. The presented workflow and findings from this study provide valuable insights into powder mixing for the development of custom alloys for rapid material screening in LPBF