Alloys, Volume 1, Issue 2 (September 2022) – 6 articles

Application of polycrystalline hexagonal close packed (HCP) metals in engineering designs has been constrained by their anisotropic responses due to twinning and limited plasticity. In deformation, twins most often initiate at grain boundaries (GBs), and thicken and propagate across the grain. In this work, the GB twin embryos in Mg and Mg alloys, and the conditions that influence their propagation are investigated. Using a micromechanical crystal plasticity model, the role of embryo shape on the driving forces prevailing at the embryo boundaries that could support its expansion is studied. The modeled embryos are either planar, extending more in the shear direction than normal to the twin plane, or equiaxed. Results show that the thinner the embryo, the greater the driving forces for both thickening and forward propagation. Alloys with low prismatic-to-basal critical resolved shear stress (CRSS) ratios promote embryo thickening and large CRSS values for the slip mode that primarily accommodates the twin shear encourage propagation. The neighboring grains with orientations that enable local accommodation of the embryo twin shear by pyramidal slip promote forward propagation but have little effect on thickening. When two like embryos lie along the same GB, their paired interaction promotes forward propagation but hinders thickening. Full article

In this paper, a perfluoropolyether (PFPE) micellar solution was effectively deposited on metallic substrates using a dip-coating process to enhance brass and nickel aluminum bronze (NAB) corrosion resistance. Particular attention was paid to the aesthetic results as well. Enabling the metallic substrates hydrophobic to facilitate water and moisture removal was the key concept of this work. The corrosion resistance of the as-received and coated metals was investigated via a salt spray chamber test. The study focused on the characterization of the polymeric coating via dynamic light scattering and wettability tests, while the substrates were assessed with traditional metallographic techniques. The preparation of the polymeric solution was important in determining the final corrosion resistance of the two substrates. Noteworthy was the effectiveness of the PFPE-based coating when it was applied to the brass rather than the NAB. Moreover, the polymer concentration of the dip-coating polymeric emulsion was the most significant factor to obtaining adequate protection: higher polymer concentrations resulted in a decrease in corrosion resistance. Full article

The impact of the artificial aging response on the microstructure and tensile mechanical properties of aluminum alloy 6156 was investigated. Specimens were artificially aged at three different artificial aging temperatures and for various holding times to investigate all possible aging conditions, including the under-aged (UA), peak-aged (PA) and over-aged (OA) tempers. Microstructural investigation as well as tensile tests were performed immediately after the isothermal artificial aging heat treatment. An almost 50% increase in yield stress (around 340 MPa) was noticed in the PA temper and this was attributed to the precipitation of β′ and Q′ phases, consistent with the modelling predictions. This high yield stress value is accompanied by high values of elongation at fracture (>10%) that is essential for damage tolerance applications. The lack of large or interconnected grain boundary precipitates contributes to this high elongation. Slanted fracture was noticed for both UA and PA tempers, exhibiting a typical ductile and shear fracture mechanism. At the OA temper, coarsening of the precipitates along with broadening of the precipitate free zones resulted in a reduction in the strengthening effectiveness of the precipitates, and a small increase in the tensile ductility of approximately 12% was noticed. Full article

Additive manufacturing (AM) of metals can be broadly accomplished via two defined technologies: powder bed fusion and directed energy deposition. During AM fabrication, the melted feedstock material experiences fast thermal cycling due to the layer-by-layer deposition process resulting in microstructures and properties that are drastically different from the traditionally manufactured parts. For AM to become a viable process for fabricating critical components made of high-performance structural alloys, such as AlSi10Mg, a comprehensive understanding is required toward developing the process-structure-property relationships prevalent in AM. AlSi10Mg, with its good castability, strength, hardness, and dynamic properties, is typically used to fabricate structural components that are required to withstand high loads. This alloy has been consolidated predominantly by the laser powder bed fusion (L-PBF) method and several critical mechanical properties, such as fatigue, have been reported to date. This article, first, summarizes the as-deposited and heat-treated microstructures of AlSi10Mg specimens fabricated by L-PBF. Then, the article discusses the linkages among the feedstock properties, printing parameters, specimen geometry, post-processing techniques, and fatigue properties. This discussion is followed by a section on the fatigue life prediction of AlSi10Mg specimens using computational modeling. Finally, the article identifies critical research gaps and pinpoints future research opportunities. Full article

Varying contents of carbon, titanium and boron were used in the base steel composition of 0.30 wt% Si, 2.0 wt% Mn, 0.006 wt% S, 0.03 wt% Nb, and 30–35 ppm N. Hot ductility tests were performed with Gleeble-3800, after the steel sample was in-situ melted, solidified, and cooled to the test temperature. Investigation was completed with thermodynamic and kinetic simulations. The best results were obtained for steels containing 58–100 ppm B and 35 ppm Ti. They showed very good hot ductility of 80–50% RA within the temperature range between 1250 °C and 800 °C. It was shown that titanium and boron were effective in improving the hot ductility. Titanium protected boron from binding into BN and was low enough to prevent excessive (Ti,Nb) carbonitride precipitation, which both could decrease hot ductility. Boron that precipitated along austenite grain boundaries as iron boride Fe₂B was very beneficial for the hot ductility of steel. Full article

Some modern alloys, such as high-entropy alloys (HEAs), are emerging with greater acceleration due to their wide range of properties and applications. HEAs can be prepared from many metallurgical operations, but mechanical alloying is considered to be one of the most simple, economical, popular, and suitable methods due to its increased solid solubility, nano-crystalline structure, greater homogeneity, and room-temperature processing. Mechanical alloying followed by the consolidation of HEAs is crucial in determining the various surface and mechanical properties. Generally, spark plasma sintering (SPS) methods are employed to consolidate HEAs due to their significant advantages over other conventional sintering methods. This is one of the best sintering methods to achieve greater improvements in their properties. This review discusses the mechanical alloying of various HEAs followed by consolidation using SPS, and also discusses their various mechanical properties. Additionally, we present a brief idea about research publications in HEA, and the top 10 countries that have published research articles on HEAs. From 2010 to 18 April 2022, more than 7700 Scopus-indexed research articles on all the fields of HEA and 130 research articles on HEA prepared by mechanical alloying alone have been published. Full article